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Armyworm Symposium 2000: Adamczyk & Sumerford


INCREASED TOLERANCE OF FALL ARMYWORMS
(LEPIDOPTERA: NOCTUIDAE) TO CRY1AC 6-ENDOTOXIN
WHEN FED TRANSGENIC BACILLUS THURINGIENSIS COTTON:
IMPACT ON THE DEVELOPMENT OF SUBSEQUENT GENERATIONS

J. J. ADAMCZYK, JR. AND D. V. SUMERFORD
Southern Insect Management Research Unit, USDA-ARS-MSA, PO Box 346, Stoneville, MS 38776

ABSTRACT
Increased tolerance to CrylAc protein was found in a population of fall armyworms,
Spodoptera frugiperda (J. E. Smith), after selection for a single generation with transgenic
Bacillus thuringiensis Berliner (Bt) cotton foliage. When fed CrylAc treated artificial diet,
larvae whose parents had fed on transgenic Bt cotton leaves had significantly higher larval
weights and a shorter time to pupation than those larvae whose parents had fed on conven-
tional cotton leaves. In addition, there was no evidence to suggest any fitness or vigor differ-
ences existed from progeny of fall armyworms that fed previously on conventional or
transgenic Bt cotton. Furthermore, tolerance of fall armyworms to CrylAc had a heritable
component in the subsequent generation based on larval weights and time to pupation.
These data show that using a common approach designed to control all intrinsically tolerant
lepidopteran species of transgenic Bt cotton identically may not be desirable.
Key Words: Spodoptera frugiperda, plant-resistance

RESUME
Aumento en tolerancia a la protein CrylAc fue encontrado en poblaciones del gusano de
otono Spodoptera frugiperda (J. E. Smith), despues de escogimiento para una generaci6n
singular de follaje de algod6n con Bacillus thuringiensis Berliner (Bt) transg6nico. Al ser ali-
mentadas una dieta artificial tratada con CrylAc, las larvas con padres que se alimentaron
de hojas de algod6n Bt transg6nica mostraron pesos larvales significativamente mayores y
menos tiempo a pupaci6n que las larvas quienes padres se alimentaron con hojas de algod6n
convencionales. Tambien, no hubo evidencia para sugerir que existen diferencias de salud o
vigor en progenie de S. frugiperda que se alimentaron previamente con algod6n convencio-
nal o Bt transg6nico. Ademas, la tolerancia de S. frugiperda a CrylAc tuvo un component
heredable en la generaci6n subsecuente basado en pesos larvales y tiempo a pupaci6n. Estos
datos demuestran que pudiera no ser deseable usar una practice comun disenada a controlar
id6nticamente a todas las species de lepid6ptera intrinsicamente tolerantes al algod6n Bt
transg6nico.


The fall armyworm, Spodoptera frugiperda
(J. E. Smith), is a destructive migratory pest of
many crops in the Western Hemisphere (Sparks
1979; Young 1979). Historically, this pest has been
a sporadic, but serious pest of conventional cotton
in the southern United States (Bass 1978; Smith
1985). This pest has the potential to damage both
conventional cotton bolls and transgenic cotton
bolls that contain an insecticidal CrylAc 8-endot-
oxin from the soil bacterium, Bacillus thuringien-
sis Berliner (Bt). The damage to bolls of transgenic
Bt cotton caused by the fall armyworm can be
more extensive than other lepidopterous pest of
cotton including bollworms, Helicoverpa zea (Bod-
die), tobacco budworms, Heliothis virescens (F.),
and beet armyworms, Spodoptera exigua (Hiib-
ner) (Bagwell 1994; Adamczyk et al. 1998a). Al-
though application rates of foliar insecticides are
often reduced for bollworms found on transgenic
Bt cotton, possibly due to reduced fitness or vigor
of individuals (Brickle et al. 1999), local outbreaks


of fall armyworms on transgenic Bt cotton often
need full application rates of foliar insecticide
treatments to keep these populations below eco-
nomic injury levels (Hood 1997; Smith 1997).
Although certain lepidopterous pests of cotton
are very susceptible to current transgenic Bt
technology [e.g. tobacco budworms and pink boll-
worms, Pectinophora gossypiella (Saunders)], fall
armyworms, bollworms, and soybean loopers,
Pseudoplusia includes (Walker) are only sub-le-
thally effected by the CrylAc 8-endotoxin (MacIn-
tosh et al. 1990, Wilson et al. 1992, Halcomb et al.
1996, Adamczyk et al. 1998b, and Sumerford &
Solomon 2000a). It seems that the CrylAc 8-en-
dotoxin found in current transgenic Bt cotton va-
rieties does not provide sufficient mortality to fall
armyworm larvae, but only slows larval develop-
ment (Adamczyk et al. 1998b). Thus, application
of foliar insecticides must be used to control this
pest on current transgenic Bt cotton varieties
(Smith 1997).







Florida Entomologist 84(1)


Few studies have examined the impact CrylAc
8-endotoxin has on subsequent generations of Lep-
idoptera. Lambert et al. (1998) showed that the in-
creased tolerance of bollworm larvae to transgenic
Bt cotton can occur in subsequent generations,
although complex interactions (i.e., genetic vs.
environmental) were not sufficiently resolved.
Furthermore, in a similar study using fall army-
worms, the effect of selection for a single genera-
tion with transgenic Bt cotton foliage on survival
and development of fall armyworms could not be
fully characterized (Adamczyk et al. 1998b).
It seems that tolerance to Bt is heritable
among certain species of Lepidoptera. Sumerford
& Solomon (2000b) showed a genetic component
for variation in larval development among H. zea
feeding on CrylAc diet. The authors also found
that selecting for more optimally growing larvae
was correlated with improved survivorship when
larvae were exposed to CrylAc. This study was
conducted in two parts: 1) to determine if in-
creased or decreased tolerance of CrylAc 8-endot-
oxin was found in a population of fall armyworms
after selection for a single generation with trans-
genic Bt cotton foliage, and 2) to determine if off-
spring of more tolerant individuals also exhibited
greater tolerance of CrylAc during the subse-
quent generation.

MATERIALS AND METHODS
P, Generation
A fall armyworm colony (obtained from Dr.
Frank Davis (retired), USDA, ARS, CHPRRU at
Mississippi State University) was utilized in all
tests. Females from this colony are annually out-
crossed with wild, pheromone trapped males to
maintain genetic heterogeneity and traits
present in field individuals. Larval and adult
rearing as well as egg harvesting were conducted
as described in Adamczyk et al. (1998b).
Three colonies of fall armyworms were estab-
lished from the original colony mentioned above.
Larvae were reared until pupation on artificial
diet, conventional cotton leaves, and transgenic
Bt cotton leaves as described in Adamczyk et al.
(1998b) and modified in Adamczyk et al. (2000).
Individual pupae were separated based on larval
host (colony designation: NBT, BT, and DIET;
reared on conventional leaves, transgenic Bt
leaves, and artificial diet, respectively) and equal
numbers of pupae (100) were then placed in 3.79
liter cylindrical containers for moth emergence.
Adult rearing and egg harvesting were conducted
as described in Adamczyk et al. (1998b).

G, Experiment
To examine the effects CrylAc 8-endotoxin had
on a subsequent generation of fall armyworms, G,
neonates from all colonies were placed on artifi-


cial diet incorporated with a lyophilized powder of
MVP II containing 19.7% CrylAc by weight (puri-
fied CrylAc; Monsanto Co., St., Louis, MO) using
the method described in Sumerford & Solomon
(1999). Thirty neonates were placed in 28.6 ml
cups (1 per cup) containing approximately 5.0 ml
of CrylAc diet and replicated twice. In addition,
the same cohort of individuals from the same
three colonies was reared on non-CrylAc diet as a
control to determine if vigor differences existed
among colonies. In a preliminary experiment, it
was determined that a dose of 10.0 pg/ml of
CrylAc slowed larval development of fall army-
worms very similar to transgenic Bt cotton.
Therefore, this diagnostic concentration was used
in all tests. Survival of larvae at 7 days after ex-
posure (DAE), survival to pupae, larval weights
at 7 DAE, and time to pupation were recorded.
Survival analysis between colonies for each dose
was conducted with G-tests using PROC FREQ
(SAS Institute 1998). All mean weights and times
were log transformed before analyzed using
REML-ANOVA (PROC MIXED; Littell et al. 1996).

G2 Experiment

To determine if tolerance of fall armyworms to
CrylAc had a heritable component, moths from
the above colonies were pooled and the subse-
quent generation tested. Regardless of what the
P1 larvae fed upon, equal numbers of G, larvae
from all three colonies that fed on non-CrylAc
diet were allowed to pupate, pooled, and adults
mated as described above. This G2 colony (REG)
served as a control again to account for any fit-
ness or vigor differences among colonies
Pupae from larvae reared the previous genera-
tion on CrylAc diet were separated based on time
to pupation of G, individuals. Those that had pu-
pated at 15 DAE were termed the FAST colony
and those individuals that pupated at 19 and 20
DAE were termed the SLOW colony. These pupa-
tion times were selected to insure that similar
numbers of pupae were available to develop ade-
quate colonies. All G2 colonies (REG, SLOW, and
FAST) were maintained as described above. Sur-
vival of larvae at 8 DAE, survival to pupae, larval
weights at 8 DAE, and time to pupation were re-
corded. Survival analysis between colonies for
each dose was conducted with G-tests using
PROC FREQ (SAS Institute 1998). All means
weights and times were log transformed before
being analyzed using REML-ANOVA (PROC
MIXED; Littell et al. 1996).

RESULTS AND DISCUSSION
G, Experiment

Based on very high (>85%) survival data, rear-
ing fall armyworms on transgenic Bt cotton had


March 2001







Armyworm Symposium 2000: Adamczyk & Sumerford


no effect on mortality in the subsequent genera-
tion. In addition, there were no significant differ-
ences (P > 0.05) in larval survival at 7 DAE (0 pg/
ml: X2 = 2.21, df = 2, P = 0.33; 10 pg/ml: X2 = 3.33,
df = 2, P = 0.19) and survival to pupae (0 pg/ml: X2
= 1.46, df = 2, P = 0.48; 10 pg/ml: X2 = 0.29, df = 2,
P = 0.87) among all three colonies.
Larvae that were reared on CrylAc diet
weighed significantly less (P < 0.05) and took sig-
nificantly more time to pupate (P < 0.05) than
those larvae reared on non-CrylAc diet which is a
reported sub-lethal effect observed for fall army-
worms feeding on transgenic Bt cotton (Adam-
czyk et al. 1998b) (Figs. 1 and 2). Significant
differences (P < 0.05) among colonies (larval
weights: F = 12.27; df= 2, 345; P < 0.001, time to
pupation: F = 13.19; df = 2, 319; P < 0.001) and
diet (larval weights: F = 541.24; df = 1, 345; P <
0.001, time to pupation: F = 329.58; df = 1, 319;P
< 0.001) were observed as well as colony by diet
interactions (larval weights: F = 5.76; df = 2, 345;
P = 0.004, time to pupation: F = 17.47; df= 2, 319;
P < 0.001). In addition, based on larval weight
and time to pupation for larvae feeding on non-
CrylAc diet, again there was no evidence to sug-
gests any fitness or vigor differences existed
among the three colonies (P > 0.05).
It appears that rearing fall armyworms on
transgenic Bt cotton caused increased tolerance
in the subsequent generation to CrylAc. When
fed CrylAc diet, larvae whose parents had fed on
transgenic Bt cotton leaves (BT) had significantly
(P < 0.05) higher larval weights at 7 DAE and a
shorter time to pupation than those larvae whose
parents had fed on conventional cotton leaves
(NBT) (larval weights: t = 5.24, df= 345,P < 0.001


180- -
160 a
E14o a --- NBT -


S" o L- DIET-
so) o
40


0 JpgIml 10 pgIml

Concentration of CrylAc

Fig. 1. Mean larval weights at 7 days after exposure
(DAE) for fall armyworms fed non-CrylAc diet (0 ig/ml)
or CrylAc diet (10 pg/ml). NBT, BT, and DIET colonies
= previous generation reared on conventional cotton
leaves, transgenic Bt cotton leaves, and non-CrylAc
diet, respectively. Columns with the same letter are not
significantly different (a = 0.05) from one another
(REML-ANOVA; PROC MIXED; Littell et al. 1996).


20-
19- NBT



18-
[] DIET *c d



13-
0 pg/ml 10 pg/ml

Concentration of CrylAc

Fig. 2. Mean time to pupation for fall armyworms fed
non-CrylAc diet (0 pg/ml) or CrylAc diet (10 pg/ml).
NBT, BT, and DIET colonies = previous generation
reared on conventional cotton leaves, transgenic Bt cot-
ton leaves, and non-CrylAc diet, respectively. Columns
with the same letter are not significantly different (a =
0.05) from one another (REML-ANOVA; PROC MIXED;
Littell et al. 1996).


(LSMEANS); time to pupation: t = -7.59, df = 319,
P < 0.001 (LSMEANS)] (Figs. 1 and 2).

G2 Experiment

As in the G, experiment, there was no indica-
tion that G2 larvae were less fit or vigorous from
feeding on CrylAc diet than from feeding on non-
CrylAc diet. In fact, survival of pupae for the
FAST colonies was significantly higher than the
SLOW or REG colonies (Fig. 3).
Based on larval weights and time to pupation,
increased tolerance to CrylAc was inherited
among individuals in the subsequent generation
(Figs. 4 and 5). Significant differences (P < 0.05)
among colonies (larval weights: F = 20.78; df = 2,
348;P < 0.001, time to pupation: F = 38.06; df= 2,
309; P < 0.001) and diet (larval weights: F =
695.25; df = 1, 348;P < 0.001, time to pupation: F
= 1360.96; df = 1, 309;P < 0.001) were observed as
well as colony by diet interactions (larval weights:
F = 15.00; df = 2, 348;P < 0.001, time to pupation:
F = 24.27; df = 2, 309; P < 0.001). When fed
CrylAc diet, larvae from the FAST colony had sig-
nificantly (P < 0.05) higher larval weights at 8
DAE and a shorter time to pupation than those
larvae from the SLOW (larval weights: t = 8.06, df
= 348, P < 0.001 (LSMEANS); time to pupation: t
= -9.66, df = 309, P < 0.001 (LSMEANS)] or REG
colonies (larval weights: t = -5.46, df = 348, P <
0.001 (LSMEANS); time to pupation: t = 4.55, df =
309, P < 0.001 (LSMEANS)]. Furthermore, based
on time to pupation, a heritability estimate was
calculated that further suggests tolerance to
CrylAc was inherited in the subsequent genera-
tion (h2 ST = 0.49). In addition, based on larval





Florida Entomologist 84(1)


A) At 8 DAE
o100 1-*i


0 pg/ml 10 pgI/m


B) To Pupae
100-( _,


P91M


10 Plgml


Concentration of CrylAc
Fig. 3. (A) Mean larval survival of fall armyworms at 8 days after exposure (DAE) and (B) to pupae when fed:
(a) non-CrylAc diet (0 pig/ml) or (b) CrylAc diet (10 pig/ml). FAST and SLOW colonies = previous generation pu-
pated at 15-16 DAE and 19-20 DAE, respectively; REG colony = previous generation reared on non-CrylAc diet.
Columns separated by dose with the same letter are not significantly different (a = 0.05) from one another (likeli-
hood ratio chi-square analysis using PROC FREQ; SAS Institute 1998).


CM



0
iU)


0
0~
L_


* FAST
D SLOW
DREG


March 2001







Armyworm Symposium 2000: Adamczyk & Sumerford


0 400 FAST
0) E 350 a FAST

p300 1- SLOW
__ 250
200oo REG
')150
100
50
0
0 pgIml 10 pg/ml

Concentration of CrylAc

Fig. 4. Mean larval weights at 8 days after exposure
(DAE) for fall armyworms fed non-CrylAc diet (0 gg/ml)
or CrylAc diet (10 gg/ml). FAST and SLOW colonies =
previous generation pupated at 15 DAE and 19-20 DAE,
respectively; REG colony = previous generation reared
on non-CrylAc diet. Columns with the same letter are
not significantly different (a = 0.05) from one another
(REML-ANOVA; PROC MIXED; Littell et al. 1996).

weight and time to pupation for larvae feeding on
non-CrylAc diet, there was no evidence to sug-
gests any fitness or vigor differences existed
among the FAST and SLOW colonies (P > 0.05),
although the REG colony took significantly longer
to pupate than either the FAST or SLOW colonies
(P > 0.05).
The assumption that sub-lethal effects from a
single generation of exposure of fall armyworms
to transgenic Bt cotton has a negative impact on
fitness or vigor in the subsequent generation
seems to be inaccurate. Although some studies


20

18-

16

E 14

i12

10


d
N FAST
-- SLOW
DREG


0 pglm
0 pg/m I


10 pglml


Concentration of CrylAc

Fig. 5. Mean time to pupation for fall armyworms fed
non-CrylAc diet (0 ig/ml) or CrylAc diet (10 ig/ml).
FAST and SLOW colonies = previous generation pu-
pated at 15 DAE and 19-20 DAE, respectively; REG col-
ony = previous generation reared on non-CrylAc diet.
Columns with the same letter are not significantly dif-
ferent (a = 0.05) from one another (REML-ANOVA;
PROC MIXED; Littell et al. 1996).


have suggested that negative maternal effects
can be transmitted by H. zea parents feeding on
transgenic Bt cotton to their offspring (Lambert
et al. 1998), no indications of this occurred with
fall armyworms. Studies have further shown that
reduced application rates of foliar insecticides can
be used for H. zea on transgenic Bt cotton com-
pared to conventional cotton, possible due to re-
duced vigor of larvae feeding on CrylAc (Brickle
et al. 1999). Our data suggests that not all lepi-
dopterous pests of cotton that are intrinsically
tolerance to CrylAc may be controlled identically
on transgenic Bt cotton. Because more than one
generation of fall armyworms can attack trans-
genic Bt cotton in one season, future work will be
needed to determine if larvae are more tolerant to
CrylAc in later generations compared to previous
generations in naturally occurring populations.

ACKNOWLEDGMENTS

The authors would like to thank Drs. C. Abel and
W. R. Meredith for review of this manuscript. In addi-
tion, we thank Ms. L. Inmon and Ms. J. Holcomb for
their diligent efforts in insect rearing. Fall armyworms
were obtained from F. Davis, USDA-ARS-CHPRRU-
Mississippi State, MS. Mention of a commercial or pro-
priety product does not constitute an endorsement by
the U.S. Department of Agriculture for its use.

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CHURCH, B. R. LEONARD, AND J. B. GRAVES. 1998a.
Susceptibility of conventional and transgenic cotton
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endotoxin to fall armyworm (Lepidoptera: Noctu-
idae) and beet armyworm (Lepidoptera: Noctuidae)
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ADAMCZYK J. J., JR., J. W. HOLLOWAY, G. E. CHURCH,
B. R. LEONARD, AND J. B. GRAVES. 1998b. Larval
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cotton expressing the Bacillus thuringiensis
CryIA(c) 6-endotoxin. J. Econ. Entomol. 91: 539-545.
ADAMCZYK, J. J., JR., L. C. ADAMS, AND D. D. HARDEE.
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different protein levels among plant parts and var-
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wide Cotton Conf., National Cotton Council, Mem-
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HALCOMB, J. L., J. H. BENEDICT, B. COOK, AND D. R.
RING. 1996. Survival and growth of bollworm and to-
bacco budworm on nontransgenic and transgenic
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doptera: Noctuidae). Environ. Entomol. 25: 250-255.
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it made, pp. 1223-1224. In Proc. Beltwide Cotton
Conf., National Cotton Council, Memphis, TN.
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tation to Bt toxin?, pp. 1033-1037. In Proc. Beltwide
Cotton Conf., National Cotton Council, Memphis, TN.
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Florida Entomologist 84(1)







Armyworn Symposium 2000: Stewart et al.


COMBINING EXCLUSION TECHNIQUES AND LARVAL DEATH-RATE
ANALYSES TO EVALUATE MORTALITY FACTORS OF SPODOPTERA EXIGUA
(LEPIDOPTERA: NOCTUIDAE) IN COTTON

S. D. STEWART', L. C. GRAHAM2, M. J. GAYLOR3 AND L. A. VANDERBERG4
1Department of Entomology and Plant Pathology, Mississippi State University, MS 39762

'Department of Entomology, Alabama Agricultural Experiment Station, Auburn University, Auburn, AL 36849

'801 Carter Road, Prattville, AL 36067

4Mail Stop E529, Los Alamos National Laboratory, Los Alamos, NM 87544

ABSTRACT

By combining pesticide exclusion and cage exclusion techniques, the efficacy of natural ene-
mies in reducing populations of Spodoptera exigua (Hubner), the beet armyworm, larvae
was effectively demonstrated. Larval collections added information about parasitism and
disease, and when combined with data from insecticide treatments, demonstrated that dif-
ferences in S. exigua population densities usually were due to the action of predators. Death-
rate analyses demonstrated that much mortality due to parasitism was contemporaneous
with death from predation. When predator populations were not reduced by insecticides,
most indispensable natural mortality was due to predation. When predators were elimi-
nated, and S. exigua populations reached outbreak levels, most larvae died from disease in
1989 and from parasitism in 1990.

Key Words: Contemporaneous mortality, beet armyworm, predation, Cotesia

RESUME
Al combinar tecnicas de exclusion de pesticide yjaula, la eficacia de enemigos naturales para
reducir poblaciones de Spodoptera exigua (Htbner) fueron demostradas efectivamente. Co-
lectas de larvas anadieron informaci6n sobre parasitismo y enfermedad, y al ser combinadas
con datos de tratamientos con insecticide, demostraron que diferencias en densidad de po-
blaci6n de S. exigua usualmente fueron debidas a la acci6n de predadores. Analices de indices
de muerte demostraron que gran parte de la mortalidad debido a parasitismo fue contempo-
ranea con muerte por predaci6n. Cuando poblaciones de predadores no fueron reducidas por
insecticides, la mortalidad natural mas indispensable fue debida a predaci6n. Cuando los
predadores fueron eliminados, y poblaciones de S. exigua alcanzaron niveles epid6micos, la
mayoria de las larvas murieron por enfermedad en 1989 y de parasitismo en 1990.


Evaluating the impact of natural enemies is a
critical part of understanding pest population dy-
namics and of developing IPM systems (Luck et
al. 1988; Sterling et al. 1989). One of two major
approaches is usually taken to study biological
control by indigenous agents in agricultural sys-
tems. In the first, exclusion of natural enemies
with insecticides, cages, or other techniques is
used to free pest populations from the action of
the natural enemies. Each exclusion method has
biases associated with it, but these biases may be
at least partially overcome by combining methods
(Luck et al. 1988). Densities of pest populations
are then compared to densities of populations
that are exposed to biological control agents
(Luck et al. 1988). These studies have been used
effectively to demonstrate that insecticide appli-
cations can disrupt natural enemy populations
and lead to secondary pest outbreaks. However,
insecticides also may affect insect populations by


direct stimulation of fecundity (hormoligosis) or
by indirect stimulation of fecundity (trophobiosis)
(Risch 1987; Kerns & Gaylor 1993b). Thus, with-
out further evidence, mechanisms of outbreak in-
duction may be unclear.
The second of the common approaches to
studying biological control in agroecosystems
uses one or more of several techniques (reviewed
in Luck et al. 1988) to identify natural enemies
that attack a pest. The importance of each natu-
ral enemy is then ranked by the proportion of a
host population that is parasitized, diseased or
preyed upon at various time intervals. Once mor-
tality agents are identified, numerical and func-
tional responses of agents, or groups of agents, to
changes in pest densities may be determined. Ef-
fects of natural enemies identified by these tech-
niques may then be incorporated into pest
models. However, Van Driesche (1983) and Van
Driesche et al. (1991) explained why this ap-







Florida Entomologist 84(1)


proach is inadequate for explaining host mortal-
ity over a generation. Also, evidence that a
particular natural enemy or group of enemies can
reduce, or even regulate, a pest population is not
adequate evidence that the enemies do reduce the
population. Different natural enemies may re-
spond differently to temperature, prey availabil-
ity or density (Sterling et al. 1989). Thus, any of
several agents may be capable of reducing a pest
population under specific conditions. Also, the ac-
tion of one natural enemy may be masked by the
actions of contemporaneous mortality factors.
Contemporaneous mortality factors are two or
more factors that attack a host more or less simul-
taneously, although death ultimately may be due
to a single factor (Royama 1981). For example, an
individual insect may be infected by a disease,
which would ultimately kill it, but also be parasit-
ized by a parasitoid.
The influences of contemporaneous mortality
factors on insect population dynamics may be de-
termined with life-tables (Royama 1981; Gould et
al. 1990). Death-rate analysis may be used to es-
timate mortality rates due to contemporaneous
mortality factors as one step in the construction of
life tables (Bellows et al. 1992). Marginal attack
rates are attack rates by individual mortality
agents that would occur in the absence of other
mortality agents acting on the same host
(Royama 1981). Marginal attack rates, which
may be calculated from observed death rates
(Royama 1981; Gould et al. 1990), are particu-
larly appropriate in death-rate analysis when the
action of one or more mortality agents is difficult
to detect (Bellows et al. 1992).
Many of these techniques and concepts, which
are commonly used in population and community
ecology, are relevant to IPM. However, for reasons
that are primarily based on the historical separa-
tion between applied and basic research (Levins
& Wilson 1980), these techniques have been used
little by agricultural scientists.
Life tables alone can not be used to document
the efficacy of natural enemies (Luck et al. 1988).
However, an effective method of assessing the
role of natural enemies in host population dynam-
ics is to contrast life-tables for experimentally
manipulated populations, in which one popula-
tion lacks specific natural enemies and the other
population is attacked by the enemies (Bellows et
al. 1992).
Spodoptera exigua (Hiibner), the beet army-
worm, is an induced pest of many crops through-
out the world. Historically, S. exigua outbreaks in
cotton have been common in the western United
States, but serious outbreaks also occur in the
Southeast. Until recent years, these outbreaks in
cotton have been difficult to control with insecti-
cides and may result in complete destruction of
some fields (Smith 1989). However, new insecti-
cides such as spinosad (Tracer, Dow Agrosciences,


Indianapolis, IN) are relatively effective against
S. exigua larvae (Halcomb et al. 1998), although
somewhat expensive.
S. exigua is attacked by several predators and
parasitoids (Eveleens et al. 1973; Pearson 1982;
Oatman et al. 1983; Alvarado-Rodriguez 1987)
and by protozoan, fungal and viral diseases
(Smits 1987). Eveleens et al. (1973) and Hogg &
Gutierrez (1980) concluded that in California cot-
ton, S. exigua populations are normally held be-
low economic injury levels primarily by predators
feeding on eggs and small larvae. Parasitoids and
disease apparently were less important as natu-
ral mortality agents of non-outbreak populations
(Pearson 1982). A nuclear polyhedrosis virus
(NPV) was the most important pathogen in S. ex-
igua populations attacking tomatoes in Mexico
(Alvarado-Rodriguez 1987) or cotton in California
(Pearson 1982). In 1988, S. exigua outbreaks on
cotton in Alabama were eventually controlled pri-
marily by a naturally occurring NPV epizootic
(Smith et al. 1989). In fields where the epizootic
did not develop, rates of parasitism by a braconid,
Cotesia marginiventris (Cresson), ranged from
23-43% (M. J. G., unpublished data). In Georgia
and northern Florida, C. marginiventris parasit-
ized 46% of the S. exigua larvae collected from cot-
ton (Ruberson et al. 1993). More recently, Stewart
et al. (1996) presented circumstantial evidence
that S. exigua problem often coincide to areas
where intensive insecticide applications are made
for other pests, such as during intensive boll wee-
vil eradication, Anthonomus grandis grandis Bo-
heman, efforts.
Thus, the importance of biotic mortality fac-
tors on S. exigua outbreaks has been established.
However, for reasons outlined in Van Driesche et
al. (1991), none of these studies adequately deter-
mined effects of mortality factors on life stages
over a S. exigua generation or determined effects
of contemporaneous mortality factors on popula-
tion dynamics. In this study, we combined insecti-
cide and cage exclusion techniques with larval
collections and death rate analyses to quantify
sources of S. exigua mortality in cotton.

MATERIALS AND METHODS

In 1989 and 1990, 'DPL90' cotton was planted
in = 0.3 ha plots at the Wiregrass Substation of
the Alabama Agricultural Experiment Station in
Henry County, AL. In 1989, untreated plots were
not possible because the area was within an active
boll weevil eradication program. Our treatments
were applications of malathion (Cythion 46.2%
RTU, American Cyanamid Company, Princeton,
NJ; applied at 1.4 kg [AI]/ha) or methyl parathion
6 EC (formerly marketed by Cheminova, Wayne,
NJ; applied at 0.6 kg [AI]/ha), each applied to four
main plots in a randomized complete block design.
Both insecticides are effective against boll weevil


March 2001







Armyworn Symposium 2000: Stewart et al.


and most predators and parasitoids but not
against S. exigua. Insecticides were applied with
ground equipment every four to eight days.
Boll weevils were less numerous in 1990, and
malathion applications were mandated by the
eradication program only on 3 and 6 July. In 1990,
main plots were four insecticide treatments: (1)
k-cyhalothrin (Karate 1E, Zeneca Ag Products,
Wilmington, DE) applied alone at 0.028 kg (AI)/
ha, (2) diflubenzuron (Dimilin 25 W wettablee],
Uniroyal Chemical Company, Middlebury, CT) + a
crop oil (Super Savol, Leffingwell, Brea, CA)
(0.036 kg [AI] + 0.16 kg/ha), (3) a combination
treatment of -cyhalothrin + diflubenzuron + crop
oil (0.028 kg [AI] + 0.036 kg [AI] + 0.16 kg/ha) and
(4) no insecticide. Four replicates of each insecti-
cide treatment were used.
Diflubenzuron was applied to treatments 2
and 3 on 29 June, 20 and 27 July and 17 August.
k-cyhalothrin was applied to treatment 1 at 3- to
10-d intervals from 29 June to 24 August and to
treatment 3 from 3 to 24 August. k-cyhalothrin
was tank mixed with the diflubenzuron on 29
June, 20 July and 17 August in treatment 3. X-cy-
halothrin is not effective against S. exigua, but it
reduces populations of most predatory arthropods
(Smith et al. 1993). Diflubenzuron may be effec-
tive against some S. exigua populations (Coudriet
& Seay 1979; Ruberson et al. 1993; Smith et al.
1993) and is relatively non-damaging to popula-
tions of beneficial arthropods (Keever et al. 1977;
Deakle & Bradley 1982).
Larval S. exigua and predator populations were
estimated during both years with 1 to 3 drop-cloth
samples, each sampling 1.8 row-m, per plot taken
one or two times weekly. In 1989, weekly mean
numbers of S. exigua were estimated. Larvae were
not separated by size. In 1990, mean numbers
were estimated for S. exigua in each of three size
classes: small (first and second stadia), medium
(third stadium) and large (fourth and fifth stadia).
Effects of insecticide treatments on weekly mean
numbers of predators and S. exigua larvae were
compared by analysis of variance and, when sig-
nificant main effects were found, means were sep-
arated with Fisher's LSD using the PROC GLM
procedure (SAS Institute 1988) at a = 0.05.
The combined effect of predators and parasi-
toids on S. exigua survival was determined using
exclusion cages similar to those of Rice & Wilde
(1988) and Kerns & Gaylor (1993a). Cages were 2
liter plastic bottles with two 13 x 9 cm windows
covered with cloth mesh. A Velcro closure was
used on one window for access to the interior of
the cage. In 1989, cages were of three mesh sizes:
large (6.4 mm diam. opening), medium (1.5 mm
diam. opening), and small (NoSeeum netting,
Balson Hercules, Providence, RI). The small mesh
excluded all predators and parasitoids. The me-
dium mesh excluded large predators and parasi-
toids but allowed small predators and parasitoids


access to the S. exigua larvae. The large mesh al-
lowed access by most invertebrate predators and
parasitoids. Only small and medium mesh cages
were used in 1990. Because methods of disease
spread in S. exigua populations are unknown,
proportions dying from disease were assumed to
be equal in all cages and in the field.
Each week, one cage with each of the mesh
sizes was placed on individual leaves on the pe-
riphery of separate plants in a subplot of each
main plot. Subplots were 3-m sections of one row
of cotton. Subplots were isolated from surround-
ing cotton by removing all plants from the ends of
the subplots for a distance of = 2 m on each end
and all cotton from the 3-m sections of adjacent
rows. An egg mass (= 25 eggs) within one day of
hatching or = 25 newly closed larvae were placed
into each cage. All eggs or larvae were from a lab-
oratory colony, reared on a meridic diet, estab-
lished in 1988 from S. exigua collected from cotton
and periodically infused with wild males. Cages
were moved to other leaves within the same sub-
plot when the larvae had consumed most of the
original leaf.
In 1990 S. exigua populations were established
outside cages in separate subplots instead of in
large mesh cages. A S. exigua egg mass from the
laboratory colony or from a natural infestation in
the same main plot was placed on the ventral side
of a leaf to simulate a natural infestation. It was
difficult to find all larvae on large plants in late-
season, and large plants provided more food for
developing larvae. Therefore, subplots were
thinned to 10 contiguous plants in midseason. For
late-season releases, subplots were thinned to 3
contiguous plants per subplot. During both years,
caged and uncaged larvae were counted 3 to 5
times weekly until all had died or pupated.
Because stadia could not be accurately deter-
mined in the field, a developmental rate model
(Ali & Gaylor 1992) was used to estimate S. ex-
igua stadia on each sample date. Daily maximum
and minimum temperatures were measured at a
weather station that was within 1 km of the plots.
Kerns & Gaylor (1993a) found no differences in
temperatures inside or outside cages placed
within the cotton canopy.
Larval mortality was estimated for each cohort
and each mesh size. Totals, instead of means,
were used because of initial differences in num-
bers of first instar larvae in individual cages. Ini-
tial population size for small larvae was
arbitrarily set at 1,000. Mortality was estimated
by multiplying the proportion of larvae surviving
from one stadium to the next by 1,000. Because
survivorship curves included only four data
points, regression analyses were not performed.
Instead, survivorship within cohorts for larvae in
cages with different mesh sizes were compared
with 3 x 4 contingency tables using the PROC
FREQ/CHISQ procedure (SAS Institute 1988) at







Florida Entomologist 84(1)


df = 6, a = 0.05. When cage effects were found, dif-
ferences in survivorship between cages were com-
pared with 2 x 4 contingency tables (df = 3, a =
0.05). Differences between cages in survivorship
for each stadium (first and second stadia were
combined) were compared with 2 x 2 contingency
tables (df = 1, a = 0.05).
To determine the incidence of disease and par-
asitism, larvae were collected from each main plot
2-4 times weekly, placed into individual plastic
cups containing velvetbean caterpillar diet
(Greene et al. 1976) chilled and returned to the
laboratory. When available, larvae were collected
from drop cloth samples and by visually search-
ing plants in appropriate plots. However, each
week 50 to 100 eggs or neonate larvae also were
placed on cotton in a third subplot. Larvae were
collected from these artificial infestations when
natural infestations were low. When sufficient
numbers were present, at least five larvae of each
of the three size classes (small, medium and
large) were collected from each plot on each collec-
tion date. Collected larvae were examined daily in
the laboratory to determine their fate.
Immature parasitoids attacking S. exigua are
difficult to identify. Thus, rates of parasitism were
based on emergence of adult parasitoids. Patho-
gens were not isolated and cultured. Instead, es-
timates of disease incidence were based on visual
symptoms. Larvae in which internal organs and
integument remained intact, with minimal dark-
ening of the integument after = 24 h, were classed
as dying of unknown causes. Cadavers classed as
"fungal infected" collapsed and were covered with
mycelia within a few hours of death. Larvae were
judged to have died of "other diseases" if the inter-
nal organs liquefied or the integument became
fragile within = 24 h of the death of the larva.
These are symptoms of acute infection by patho-
gens such as nuclear polythedrosis virus (NPV) or
by Bacillus thuringiensis Berliner (Bt).
The head capsule from the first molt after col-
lection was measured with an ocular micrometer
to determine the instar of each larva at the time
of collection. Using the developmental rate model
for S. exigua on cotton (Ali & Gaylor 1992), larval
eclosion dates were estimated.
S. exigua generations occur at about one-
month intervals (Trumble & Baker 1984). The
first S. exigua infestations normally occur in
southern Alabama cotton in July. Hence, the de-
velopmental rate model (Ali & Gaylor 1992) was
used to place all larvae into July or August co-
horts' equivalent to field generations ofS. exigua.
Contingency table analyses were used (a = 0.05)
to compare effects of insecticide treatments, lar-
val size classes, and cohorts within years on mor-
tality caused by parasitism, disease or unknown
causes. When contingency tables were significant,
differences between causes were separated with 2
x 2 contingency tables (a = 0.05).


Death-rate tables were developed for each co-
hort each year. Because of the broad-spectrum ef-
fects of both insecticide treatments used in 1989,
death-rate tables were developed from both treat-
ments combined. Data from untreated and di-
flubenzuron plots were combined in 1990 because
diflubenzuron has little effect on predator popula-
tions (Keever et al. 1977; Deakle & Bradley 1982).
Separate tables also were constructed for combi-
nation (X-cyhalothrin + diflubenzuron) plots and
for X-cyhalothrin plots.
To construct death-rate tables, the initial pop-
ulation size (lx) for small larvae was set arbi-
trarily at 1,000 because separate populations
were used to determine mortality rates. The num-
bers of larvae in each size class dying (d.) of para-
sitism, disease or "unknown" were estimated for
each cohort by multiplying the proportion of field-
collected larvae dying of each factor by 1 for the
cohort and size class.
Marginal attack rates (m) for disease, parasit-
ism and unknown mortality factors were calcu-
lated by the formulae of Gould et al. (1990):

mA= vA/(l-cmB)
and
mB = {(c-l)vA+cvB+l-[(VA-cVA-cvB-1)2-4cvB]2/2c}

where vA = proportion of hosts dying of factor A: vB
= proportion of hosts dying of factor B; c = propor-
tion of hosts dying of factor B, when A and B at-
tack the same individual. In this case, c was
assumed to be 0.5 because outcomes of competi-
tion between parasitoids and disease and "un-
known" mortality factors are unknown. Marginal
attack rates were calculated for each factor by let-
ting vA = the proportion of larvae dying of one fac-
tor and vB = the proportion dying of all other
factors except predation.
Estimating mortality due to predation is diffi-
cult because hosts that are preyed upon usually
disappear from the system. In many life tables,
mortality due to diseases and parasitoids is calcu-
lated, and predation is assumed to be the residual
mortality that is unaccounted for by other factors
(Bellows et al. 1992). This technique may under-
estimate the importance of predation because
predation may be contemporaneous with other
factors. Alternatively, predation effects may be
overestimated if mortality rates due to abiotic,
physiological, or unknown factors are high. Thus,
an independent measure of deaths due to preda-
tion is needed.
In 1989, the boll weevil eradication program
made an untreated control impossible. Thus, mar-
ginal attack rates for predators were estimated
from the cage experiment using the formula from
Royama (1981):


mB = (mA+B mA)/(1 mA)


March 2001







Armyworn Symposium 2000: Stewart et al.


where mBn = marginal attack rate of predators; mA
= marginal attack rate by parasitoids, estimated
from collected larvae; mAB, = total mortality due to
A and B. However, mB in this formula is not inde-
pendent of mA.
Because mortality was estimated from differ-
ent host populations, marginal attack rates were
used to estimate the proportion of larvae of each
size class that should have died of each factor if
all factors were acting on the same population (v).
This was done by solving the formula of Gould et
al. (1990) for vA. Thus,
vA = mA (1 cmB)
where c was assumed to be 0 when factor A was
predation because larvae killed by predators
would not produce parasitoids or disease symp-
toms. Values of 1l+1 were obtained by subtracting
total vx from 1x.
In 1990, predation rates for each S. exigua co-
hort were estimated from differences in popula-
tion densities in insecticide treatments. Based on
larval collections, the most dense S. exigua popu-
lation was assumed to have been reduced by the
action of all agents except predators. Less dense
populations were attacked by all natural enemies.
Because success rates of most predators are un-
known, we assumed that attacks by predators
were always successful. Contemporaneous at-
tacks that included predation were assumed to al-
ways be won by predators because there was no
evidence that predators were less successful in at-
tacking diseased or parasitized S. exigua than in
attacking larvae that were not affected by other
mortality factors. Thus, marginal attack rates for
predation were equal to observed mortality (v)
due to predation. To estimate the marginal attack
rate for predators, the area under the potential
population density curve for a S. exigua popula-
tion unaffected by natural enemies was first esti-
mated by:
PPj = POJ,(1-vo,)
where PPj = area under the potential population
density curve for the ith size class in thejth cohort,
PO = the area under the curve for the most dense
S. exigua population, v,o, = proportion of the popu-
lation that was calculated to have died of all
causes except predation. In all cases, except for
large S. exigua in the second cohort, the most
dense S. exigua populations were in the k-cyhalo-
thrin treatment. In the second cohort, more large
larvae were in the k-cyhalothrin + diflubenzuron
treatment than in the other treatments. The mar-
ginal attack rate for predation (me) was esti-
mated by:

mp,e = (PO, PL,)/PP,

where PL = the area under the curve for the least
dense S. exigua population. Competition among


mortality factors in a single population includes
predation. Therefore, a modified proportion (v') of
larvae of each size class that would have died of
each factor if all factors were acting on a single
population was calculated by incorporating mrn,
into the formula of Gould et al. (1990) for mA and
solving for v'. Thus,

v'A = (1 m,ed) (mA (1 (0.5 (mB + mc))))

The total of all v' for a S. exigua size class in a co-
hort was subtracted from 1x for the class to get 1l
for the subsequent size class.
Indispensable mortality (IM) is mortality that
would not be replaced in the host population by
the subsequent action of other mortality factors if
the factor under consideration were removed
(Bellows et al. 1992). Within each size class and
cohort for each year, IM was estimated for each
mortality factor by subtracting the number of lar-
vae surviving for the cohort from the number sur-
viving when the effect of the factor was removed.

RESULTS

Insecticide Exclusion

In 1989 there were few differences in predator
or S. exigua population densities due to insecti-
cide treatments (Fig. 1). The first "wild" S. exigua
egg mass was found on 17 July 1989. Larval S. ex-
igua were first counted in beat sheet samples on 9
August, but populations remained sparse until 30
August, when 3.2 + 0.95 and 5.5 + 0.23 larvae per
0.9 row-m were found in malathion and methyl
parathion-treated plots, respectively. Weekly mean
S. exigua population densities were not signifi-
cantly different between treatments (F = 0.74, 1.83,
2.57, 0.47; df = 1,36, 1,26, 1,3, 1,3; for 9, 16, and 30
August and 6 September, respectively;P > 0.05).
Total predator densities declined after 5 July
1989 in plots treated with either insecticide.
Predator populations then increased in mid- and
late-August in both treatments, but densities
were higher in the malathion-treated plots than
in the methyl parathion-treated plots on 23 (F =
3.72, df = 1,34, P < 0.05) and 30 August (F = 1.94,
df = 1,35, P < 0.05).
The imported fire ant, Solenopsis invicta Bu-
ren, was especially abundant in early season,
comprising = 90% of the predators in malathion
plots on 5 and 12 July and = 80% in the methyl
parathion plots on 5 July. When total predator
populations were least dense (2 August), ants
were only = 20% of the predator populations in
both treatments. When the total predator popula-
tion peaked again (23 August in the malathion
plots) fire ants were = 70% of the population.
Medium sized S. exigua were found in the first
1990 samples, during the week of 4 July (Fig. 2).
These larvae were from the first of three S. exigua







Florida Entomologist 84(1)


E 20 Methyl Parathion .









! Methyl Parathion 1
0









aDate














tute 1988).
0 A




Malathion treatments affected S. exiguaB
SMetnyl Parathionf small S. exigua in the July co-































othrin treatment than in the other plots on 18
July and 8 AJu 2(F = 4Ju.02, Aug 23.8,Aug 6Sep
Date

Fig. 1. Mean number of S. exigua larvae and preda-
tors per 1.8 row-pulations were during 1989. Means on the same date
not accompanied by the same letter are significantly dif-
ferent (P < 0.05) according to Fisher's LSD (SAS Insti-
tute 1988).


generations in 1990. Populations of small larvae
of the second generation peaked in mid-July and
small larvae ofin -cyhalo third generation peaked in mid-
August (Fig. 2). Thus, the assignment of larvae to
July and August cohorts represented the occur-
rence of second and third generations in 1990.
X-cyhalothrin treatments affected S. exigua
and predator population densities in 1990 (Fig. 2).
Mean numbers of small S. exigua in the July co-
hort were not different among insecticide treat-
ments (F = 2.46, 0.56, 1.81; df = 3,108, 3,89, 3,89;
for 11, 18, and 25 July, respectively;F > 0.05). Al-
though more medium larvae were in the X-cyhal-
othrin treatment than in the other plots on 18
July and 8 August (F = 4.02, and 2.8, respectively;
df = 3,89; P < 0.05), populations in all treatments
were small. Beginning on 18 July, total predator
populations were lower in the X-cyhalothrin and
combination plots than in untreated and di-
flubenzuron plots (F = 7.60, df = 3,89, P < 0.05).
On 25 July, fewer predators were in plots that had
been treated regularly with X-cyhalothrin (treat-
ment 1) than in any other treatments (F = 13.05,
df = 3,89, P < 0.05). Predator population densities
in combination plots were intermediate between
those in X-cyhalothrin-treated plots and those in
plots that were not treated with X-cyhalothrin.
When X-cyhalothrin was applied to combination
plots at frequent intervals beginning on 3 August,


.* 3

2

3 1


11 Jul 25 Jul 8 Aug 22 Aug 5 Sep
Date
Fig. 2. Mean number of (A) small, (B) medium, and
(C) large S. exigua larvae and (D) predators per 1.8 row-
m during 1990. Means on the same date not accompa-
nied by the same letter are significantly different (P <
0.05) according to Fisher's LSD (SAS Institute 1988).


predator populations were quickly reduced. From
8 August until the end of August, predator popu-
lations were not different in the X-cyhalothrin
and combination plots, and they were lower than
in plots that were not treated with k-cyhalothrin


a" D
Untreated ;,
Diflubenzuron .-* ,
Cyhalothrin ..-
Combination ]. a

S\ /b ,
...... _b


March 2001







Armyworn Symposium 2000: Stewart et al.


(F = 27.75, 19.15, 67.64 and 34.58 for 8, 15, 22
and 29 August, respectively; df = 3,89; P < 0.05).
When S. exigua populations peaked (22,22 and 29
August for small, medium and large larvae, re-
spectively), population densities for each size
class were lower in plots with dense predator pop-
ulations (not treated with k-cyhalothrin) than in
k-cyhalothrin treated plots (F = 6.23, 14.51, and
34.58 for small, medium and large, respectively;
df = 3,89; P > 0.05). S. exigua population densities
were not different between control and in di-
flubenzuron plots. Thus, in plots with dense pred-
ator populations, diflubenzuron did not further
reduce S. exigua populations. Densities of me-
dium S. exigua in combination plots were inter-
mediate between those in k-cyhalothrin-treated
and untreated plots on 22 August. Thus, difluben-
zuron reduced these population densities when
predator populations were lower.
Ants made up 48-93% of the predator popula-
tions during the first week of sampling (4 July
1990). Subsequently, ants were virtually elimi-
nated in plots treated with k-cyhalothrin at 3- to
10-d intervals. Big-eyed bugs, Geocoris spp., were
the most abundant predators in these plots. Both
ant and big-eyed bug populations increased rap-
idly in August in all plots, but big-eyed bugs were
the most abundant predators by 15 August. X-cy-
halothrin did not reduce big-eyed bug population
densities below those in untreated plots, but ants
remained less abundant in the k-cyhalothrin-
treated plots (F = 8.15, 14.30, 12.78 and 7.72 for
8, 15, 22 and 29 August, respectively; df = 3,89;
P < 0.05).
Results of the insecticide exclusion experiment
provided anecdotal evidence that, at least in 1990,
predators controlled S. exigua populations. S. ex-
igua populations increased dramatically when
predator populations were eliminated by frequent
applications of k-cyhalothrin. However, effects of
contemporaneous mortality factors (disease and
parasitism) were not assessable by this experiment.

Cage Exclusion

Results of the cage exclusion experiment were
similar to the results of the insecticide exclusion
experiment. In both 1989 cohorts, more S. exigua
survived to the fifth stadium in the total exclusion
cages than in the cages that allowed access by
predators and parasitoids (x2 = 19.642 and 58.293
for July and August, respectively; df = 6;P < 0.05)
(Fig. 3). However, in July, there were no differ-
ences in survival for individual stadia. In August,
survival was greater in total exclusion cages only
during the third stadium, indicating that most of
the differences in survival were due to mortality
to medium larvae. There were no differences in
survival in no exclusion and partial exclusion
cages. In the July cohort, survival to the fifth sta-
dium was 38.6 and 13.2% in total and no exclusion


S1UU AA

I 80 :-




S Total Exclusion -r
20 Partial Exclusion .
No Exclusion

100a-

80 "''"""




-"i 4 Total Exclusion b- ".,
" 20 Partial Exclusion.g. *E..
- No Exclusion ......
0 a


3 4 5
Larval Stadia


Fig. 3. S. exigua larval survival in 1989 inside total,
partial and no exclusion cages. (A) July cohort. (B) Au-
gust cohort. Survival within stadia not accompanied by
the same letter are significantly different (P < 0.05) ac-
cording to 2 x 2 x2 tests (SAS Institute 1988).


cages, respectively, and survival was 54.2 and
12.2% in total and partial exclusion cages in the
August cohort. Thus, larval survival differed most
in the total exclusion cages versus the other cages
when predator populations were most dense.
In 1990, in plots with relatively few predators,
S. exigua survival inside total exclusion cages
(Fig. 4) was not different from survival outside
cages (X2 = 3.313, 6.019 and 0.801 for July cohorts
treated and not treated with k-cyhalothrin and
for the treated August cohort, respectively; df = 3;
P > 0.05). In July, survival outside cages in plots
not treated regularly with k-cyhalothrin (Fig. 4A)
was intermediate between that inside partial and
total exclusion cages. In k-cyhalothrin-treated
plots (i.e., few natural enemies) in July (Fig. 4B)
and August (Fig. 4D), there were no differences in
S. exigua survival inside total exclusion cages ver-
sus outside cages, but survival was lower in par-
tial exclusion cages.
More larvae survived in total exclusion cages
than outside cages in plots with dense predator
populations (Fig. 4C). Thus, exclusion of preda-
tors by cages increased S. exigua survival when
predator populations were dense, but not when
predator populations were sparse. Data from the
combination plots were included with data from
untreated plots in July but were combined with


1 & 2







Florida Entomologist 84(1)


0 1. --...::.............. ::::::::::::
100 Total Exclusion D
80 a Partial Exclusion .*i
0 \ a No Exclusion
60

0 40 b'*

*| 20 ', ----.,.,
S---..........................
0 -
1&2 3 4 5
Larval Stadia
Fig. 4. S. exigua larval survival in 1990 outside ex-
clusion cages and inside total and partial exclusion
cages. (A) July cohort in cotton not treated with X-cyha-
lothrin at 3- to 10-d intervals. (B) July cohort in cotton
treated with X-cyhalothrin. (C) August cohort in cotton
not treated with X-cyhalothrin. (D) August cohort in cot-
ton treated with X-cyhalothrin. Survival within stadia
not accompanied by the same letter are significantly dif-
ferent (P < 0.05) according to 2 x 2 X2 tests (SAS Insti-
tute 1988).

data from cyhalothrin-treated plots in August be-
cause k-cyhalothrin dramatically reduced natural


enemy populations in August but not in July. In
all cohorts in 1990, most S. exigua mortality oc-
curred while larvae were small.
Insecticide and cage exclusion methods pro-
vided supporting evidence that S. exigua popula-
tions were controlled by natural enemies acting
primarily on small and medium sized larvae. The
k-cyhalothrin-induced outbreak apparently was
due to destruction of natural enemy populations.
However, neither exclusion method provided in-
formation about contemporaneous mortality or
the individual impact of different mortality agents
attacking incipient versus outbreak populations.

Larval Collection

Prior to 4 August 1989, few S. exigua could be
collected to determine parasitism or disease inci-
dence. Because survival of laboratory-reared and
released larvae was low, only 161 larvae were col-
lected from the July 1989 cohort; 1273 larvae
were collected from the August cohort (Table 1).
There were no differences in sources of mortal-
ity for different sizes of S. exigua larvae in July
1989 (X2 = 2.418, df = 2, P > 0.05). The most com-
mon mortality factor affecting larvae in this cohort
was "unknown" (16.2%), that may have been par-
tially attributable to handling and to the collected
larvae originating from a laboratory colony. The
first parasitoids emerged from larvae collected as
3rd instars on 20 July 1989, but little parasitism
and no disease were found in this cohort.
Disease was a more important mortality factor
in August. The first larva to die from disease was
collected during the week of 9 August 1989. It was
infected with a fungal pathogen. Rates of disease
infection increased as larvae matured. In this co-
hort, more medium than small larvae ((2 =
27.395, df = 1, P < 0.05) and more large than me-
dium larvae (X2 = 14.622, df = 1, P < 0.05) were
diseased. Most diseases were fungal diseases; 3.4,
18.9, and 35.0% of small, medium, and large lar-
vae were infected by fungi, respectively. However,
within a single week the infection rate was even
greater. On 6 September, 46 and 88% of the me-
dium and large larvae, respectively, produced
mycelia. Other diseases killed only 2.1% of the
larvae collected from the August cohort.
In August 1989, most parasites emerged from
medium larvae (Table 1). Effects on parasitism
rates of the area-wide insecticide applications ap-
plied in 1989 for the boll weevil are unknown.
In 1990, 860 and 414 larvae were collected for
the July and August cohorts, respectively. In both
cohorts, insecticide treatments had no statisti-
cally significant effect on the incidence of disease
(X2 = 5.67 and X2 = 4.09 for July and August, re-
spectively; df = 2; P > 0.05), parasitism (X2 = 2.46
and X2 = 0.24 for July and August, respectively; df
= 2;P > 0.05), or unknown factors (x2 = 3.27 and X2
= 1.27 for July and August, respectively; df = 2;


March 2001







Armyworn Symposium 2000: Stewart et al.


TABLE 1. SOURCES OF MORTALITY TO THREE SIZES OF S. EXIGUA LARVAE COLLECTED FROM COTTON.

Percent mortality

July August

Source Small Medium Large Small Medium Large

1989
Unknown 34.8 Aa 5.7 Aa 10.0 Aa 22.4 Aa 11.0 Bb 3.5 Cb
Parasitism 4.4 Aa 2.9 Aa 5.0 Aa 3.7 Bb 24.2 Aa 4.5 Bb
Disease 0.0 Aa 0.0 Aa 0.0 Aa 6.0 Cb 21.1 Ba 36.7 Aa
Total 39.2 Aa 8.6 Aa 15.0 Aa 32.1 B 56.3 A 44.7 AB
N 80 35 46 512 408 353
1990
Unknown 47.1 Aa 25.4 Ba 8.1 Cb 26.1 Aa 12.3 Ab 17.7 Aa
Parasitism 27.1 Aab 29.4 Aa 14.8 Ba 23.1 Aa 28.1 Aa 22.4 Aa
Disease 12.9 Ab 9.1 Bb 4.0 Cc 6.0 Bb 15.8 Aab 17.7 Aa
Total 87.1 A 63.9 B 26.9 C 55.2 A 56.2 A 57.8 A
N 85 330 420 134 114 147

Means within months and rows followed by the same capital letter are not significantly different according to 2 x 2 XK analysis, df= 1,P < 0.05. Means
within years and columns followed by the same lower case letter are not significantly different according to 2 x 2 XK analysis, df = 1, P< 0.05 (SAS Institute
1988).


P > 0.05). Rates of disease were low throughout
1990, and in July, disease incidence decreased as
larvae matured (Table 1). In August, rates of dis-
ease increased as larvae matured. "Unknown"
causes killed = 20% of the larvae from both 1990
cohorts. The highest rate of fungal infection
(8.8%) was in large larvae from the August cohort.
Parasitism was one of the most common causes
of mortality in both cohorts in 1990. In July,
higher rates of parasitism were found in small
and medium larvae than in large larvae. In Au-
gust, however, there was no significant difference
associated with host size.
Over both seasons, parasitoids emerged from
15% of collected S. exigua; 10, 26 and 11% of the
large, medium and small larvae, respectively,
were parasitized. The most common parasitoid
found in both years was Cotesia marginiventris
(Cresson) (det. P. M. Marsh). This species, which
attacks the larvae of at least 21 lepidopteran spe-
cies (Krombein et al. 1979), emerged from 95% of
parasitized S. exigua collected as small or me-
dium-sized larvae. Meteorus rubens (Nees) (det. P.
M. Marsh) emerged from 3% of parasitized me-
dium larvae. The tachinid Lespesia aletiae (Riley)
(det. N. E. Woodley) emerged from 86% of the par-
asitized S. exigua collected as large larvae. In
1990, the gregarious, external parasitoid, Euplec-
trus pathypenae Howard emerged from three
fourth instar S. exigua. E. comstockii Howard
(det. M. E. Schauff), emerged from one fourth in-
star. The hyperparasitoids Mesochorus disciter-
gus (Say) (det. R. W. Carlson) and Spilochalcis
hirtifemora (Ashmead) (det. E. E. Grissell) also
emerged from S. exigua collected in 1989.


Because larvae were not dissected to deter-
mine rates of parasitism, attack rates could not
be estimated directly. However, 98% of C. margin-
iventris emerged from larvae collected as small or
medium larvae in 1989 and 1990 combined. Ru-
berson et al. (1993) also found that C. marginiven-
tris oviposited primarily in small and medium
sized larvae. In contrast, only 3 of the 103 L. ale-
tiae that emerged were from S. exigua collected as
small or medium larvae. Thus, there was little
contemporaneous mortality caused by the two
most abundant parasitoids in this study.
Results of this experiment alone might lead to
the conclusion that in August 1989, fungal dis-
ease of large larvae was the most important S. ex-
igua mortality factor. C. marginiventris was the
most abundant parasitoid both years, but its ef-
fects on S. exigua population densities is unclear
from these data. Contemporaneous mortality,
even for parasitism and disease, is not addressed
by these results.

Mortality Tables

In 1989, different natural enemies were respon-
sible for most mortality in the two S. exigua cohorts
(Table 2). In July, marginal attack rates (m) and in-
dispensable mortality (IM) from all causes com-
bined were higher for small S. exigua than for the
other size classes. Thus, death of small larvae ap-
peared to be most important in the decline of this
nonoutbreak larval population. However, much of
the "unknown" mortality could be removed from
the analysis if the high mortality rates for small
larvae due to unknown causes were artifacts of

















TABLE 2. DEATH RATE ANALYSES FOR S. EX[GUA LARVAE IN 1989.

July August
Mortality
factor Stage 1 d m v1 IM 1 d m v1 IM

Unknown Small larvae 1,000 342.8 0.357 0.287 0.148 1,000 223.8 0.237 0.204 0.027
Parasitism 43.5 0.053 0.036 0.004 36.8 0.043 0.033 0.000
Disease 0.0 0.000 0.000 0.000 59.5 0.069 0.054 0.007
Predation (219.0)1 0.175 0.175 0.057 (124.6) 0.085 0.085 0.008
Total 610.3 0.586 0.498 0.263 444.7 0.434 0.377 0.051

Unknown Medium larvae 502 28.7 0.058 0.046 0.016 623 68.7 0.146 0.064 0.014
Parasitism 14.4 0.029 0.023 0.000 151.1 0.299 0.146 0.004
Disease 0.0 0.000 0.000 0.000 131.3 0.265 0.126 0.030
Predation (110.5) 0.197 0.197 0.065 (355.2) 0.387 0.387 0.112
Total 153.6 0.284 0.265 0.096 706.3 1.097 0.723 0.219

Unknown Large larvae 369 36.9 0.103 0.085 0.031 172 6.1 0.045 0.030 0.005
Parasitism 18.4 0.053 0.042 0.000 7.7 0.057 0.039 0.001
Disease 0.0 0.000 0.000 0.000 63.3 0.386 0.322 0.054
Predation (73.2) 0.154 0.154 0.048 (29.8) 0.123 0.123 0.012
Total 128.5 0.309 0.281 0.104 106.9 0.611 0.514 0.088

Pupae 265 84

'Observed mortality (d,) due to predation was from caged data and includes predation and parasitism.







Armyworn Symposium 2000: Stewart et al.


their being from a laboratory colony and of han-
dling. Marginal probabilities for total mortality of
each size class would then be nearly equal. Alter-
natively, if much "unknown" mortality was due to
insecticides, it should be included in the analysis.
Marginal attack rates and IM for predation
were similar for all S. exigua size classes, indicat-
ing that predators attacked different sizes
equally. Indispensable mortality due to predation
on all size classes combined and "unknown" mor-
tality to all sizes were similar (Table 3). Parasit-
ism and disease were of little importance to the
July cohort, and 26.5% of larvae hatching in July
survived to pupation (Table 2).
When S. exigua reached outbreak levels in Au-
gust 1989, larval mortality for the generation in-
creased dramatically (Table 2). Only 8.4% of the
August cohort pupated. The highest levels of m
and IM were for medium larvae. The parasitoid C.
marginiventris parasitized = 30% of the medium
larvae in the August cohort. However, because
much of the parasitism was contemporaneous
with other mortality factors, only 15% of medium
larvae from a single population would have pro-
duced parasitoids (v' = 0.146). Indispensable mor-
tality due to predation on medium larvae was
much higher than IM for any other mortality fac-
tor affecting this size class (Table 2). Thus, preda-
tion was most responsible for reducing the
proportion of this cohort that reached the most
damaging developmental stage. Marginal proba-
bilities of attack on medium larvae due to preda-
tion and of large larvae due to disease were about
equal. However, disease of large larvae affected a
smaller portion of the cohort than did predation
on medium larvae. Thus, IM for predation on me-
dium larvae was higher than IM for disease of
large larvae. Parasitism caused little indispens-
able mortality to this generation. When all sizes
were combined, IM for disease was higher than
for any other factor (Table 3).
Because levels of disease, parasitism and un-
known mortality were not different across insec-
ticide treatments, mean percentages of mortality
due to these factors were used to construct death-
rate analyses in 1990 (Table 4). In July, in plots
that had not been treated regularly with X-cyhal-
othrin (untreated, diflubenzuron and combina-
tion), S. exigua suffered relatively high rates of


predation on medium and large larvae. About
one-third of the large S. exigua in these plots were
attacked by predators (m = 0.343 and 0.313 in
control and combination plots, respectively). Pre-
dation caused more indispensable mortality than
any other factor attacking large larvae.
Nevertheless, because of high rates of parasit-
ism of small and medium larvae (Table 4), para-
sitism was most responsible for reducing the
density of this population before it reached the
large larvae stage. When mortality to all sizes
was combined (Table 5), parasitism caused more
indispensable mortality to the July 1990 cohort
than did predation or disease. In all insecticide
treatments in both 1990 cohorts, m values for par-
asitoids were greater for small and medium lar-
vae than for large larvae (Table 4). Thus, C.
marginiventris, which caused almost all parasit-
ism in small and medium larvae, appeared to be
the most important parasitoid.
In August 1990, contemporaneous mortality
was high in plots where predators were abundant
(untreated and diflubenzuron). For example,
when predation was precluded by collecting lar-
vae, 28% of medium larvae were parasitized (Ta-
ble 1). Thus, marginal attack rates for parasitism
were high (Table 4). However, predation rates
also were high in these plots. Predators attacked
= 45% of the medium larvae (Table 4). Because of
contemporaneous mortality, only 15% of larvae in
these plots would have died from parasitism (v' =
0.152). In these plots, predation caused more in-
dispensable mortality than any other factor in
August (Table 5). Rates of predation were low (Ta-
ble 4) where predator populations were virtually
eliminated (k-cyhalothrin treatment and in the
combination plots in August), and parasitism was
the most important mortality factor.
Natural mortality was greater for each cohort
of S. exigua larvae when predators were present
than when they were eliminated. Pupal 1l values
were less in plots with dense predator populations
than in plots with reduced predator populations.
However, even in the 1990 plots with few preda-
tors (combination plots in August and both cohorts
of k-cyhalothrin-treated), larval mortality was
greater than in 1989 (Table 2). These differences
apparently were due to higher marginal attack
rates by "unknown" factors and by parasitoids.


TABLE 3. TOTAL INDISPENSABLE MORTALITY1 TO LARVAE IN 1989.

Mortality factor July August

Unknown 0.223 0.053
Parasitism 0.005 0.006
Disease 0.000 0.118
Predation 0.208 0.086
Indispensable mortality was calculated from larval death rates by subtracting the number entering the pupal stage when the mortality factor was
included from the number entering the pupal stage when the factor was not included.









TABLE 4. DEATH-RATE ANALYSIS FOR S. EXIGUA LARVAE IN COTTON UNDER THREE INSECTICIDE REGIMES IN 1990.

July August

Stage Mortality factor 1, d, m v' IM 1 d, m v' IM

Untreated and diflubenzuron alone


Small
larvae




Medium
larvae




Large
larvae




Pupae


Unknown
Parasitism
Disease
Predation
Total

Unknown
Parasitism
Disease
Predation
Total

Unknown
Parasitism
Disease
Predation
Total




Unknown
Parasitism
Disease
Predation
Total

Unknown
Parasitism
Disease
Predation
Total

Unknown
Parasitism
Disease


1,000 471.0
271.0
129.0
38.0
909.0

200 50.7
58.7
18.2
95.0
222.6

40 3.2
5.9
1.6
13.7
24.4
19


1,000 471.0
271.0
129.0
102.0
973.0

186 47.3
54.8
17.0
44.0
163.1

54 4.4
8.0
2.2


0.037
0.018
0.005
0.001
0.077

0.012
0.014
0.004
0.018
0.077

0.002
0.004
0.001
0.010
0.021


1,000 261.0
231.0
60.0
321.0
873.0

311 38.2
87.3
49.1
140.2
314.8

77 13.7
17.3
13.7
33.8
78.5
19


0.675
0.440
0.221
0.038
1.374

0.330
0.373
0.129
0.476
1.308

0.090
0.158
0.045
0.343
0.637




0.675
0.440
0.221
0.102
1.438

0.330
0.373
0.129
0.236
1.068

0.090
0.158
0.045


0.434
0.234
0.094
0.038
0.800

0.130
0.151
0.044
0.476
0.800

0.053
0.097
0.026
0.343
0.519




0.405
0.218
0.080
0.102
0.814

0.189
0.220
0.064
0.236
0.708

0.055
0.101
0.027


1,000 261.0
231.0
60.0
147.0
699.0

390 48.0
109.7
61.7
64.8
284.2


0.316
0.284
0.081
0.321
1.001

0.162
0.338
0.204
0.451
1.155

0.229
0.282
0.229
0.438
1.178




0.316
0.284
0.081
0.147
0.827

0.162
0.338
0.204
0.166
0.870


147 26.1 0.229
33.0 0.282
26.1 0.229


X-cyhalothrin + diflubenzuron


Small
larvae


Medium
larvae




Large
larvae


0.052
0.026
0.007
0.003
0.120

0.017
0.020
0.005
0.009
0.067

0.003
0.006
0.002


0.175
0.155
0.038
0.032
0.689

0.065
0.152
0.084
0.451
0.751

0.096
0.122
0.096
0.438
0.752




0.220
0.194
0.048
0.147
0.610

0.098
0.231
0.128
0.166
0.622

0.170
0.218
0.170


0.011
0.009
0.002
0.009
0.053

0.005
0.011
0.006
0.016
0.058

0.007
0.009
0.007
0.015
0.058




0.036
0.032
0.007
0.011
0.102

0.016
0.038
0.021
0.013
0.107

0.023
0.030
0.023















TABLE 4. (CONTINUED) DEATH-RATE ANALYSIS FOR S. EX[GUA LARVAE IN COTTON UNDER THREE INSECTICIDE REGIMES IN 1990.

July August

Stage Mortality factor 1 d m v' IM 1 d m v' IM

Predation 17.0 0.313 0.313 0.013 0.0 0.000 0.000 0.000
Total 31.6 0.607 0.497 0.027 85.2 0.740 0.558 0.082
Pupae 27 65
X-cyhalothrin alone
Small Unknown 1,000 471.0 0.675 0.451 0.110 1,000 261.0 0.316 0.258 0.033
larvae Parasitism 271.0 0.440 0.243 0.054 231.0 0.284 0.228 0.029
Disease 129.0 0.221 0.098 0.014 60.0 0.081 0.056 0.007
Predation 0.0 0.000 0.000 0.000 0.0 0.000 0.000 0.000
Total 871.0 1.336 0.792 0.221 552.0 0.680 0.542 0.071
Medium Unknown 208 52.8 0.330 0.247 0.035 458 56.3 0.162 0.118 0.015
larvae Parasitism 61.0 0.373 0.288 0.042 128.6 0.338 0.276 0.035
Disease 18.9 0.129 0.083 0.011 72.3 0.204 0.153 0.019
Predation 0.0 0.000 0.000 0.000 0.0 0.000 0.000 0.000
Total 132.6 0.832 0.618 0.094 257.2 0.704 0.547 0.073
Large Unknown 79 6.4 0.090 0.081 0.006 207 36.7 0.229 0.112 0.022
larvae Parasitism 11.7 0.158 0.148 0.012 46.4 0.282 0.143 0.028
Disease 3.2 0.045 0.040 0.003 36.7 0.229 0.112 0.022
Predation 0.0 0.000 0.000 0.000 71.1 0.343 0.343 0.032
Total 21.3 0.294 0.268 0.021 190.9 1.083 0.710 0.147

Pupae 58 60







Florida Entomologist 84(1)


TABLE 5. TOTAL INDISPENSABLE MORTALITY' TO S. EXIGUA LARVAE DUE TO FOUR MORTALITY FACTORS UNDER THREE
INSECTICIDE REGIMES IN 1990.

Untreated and diflubenzuron X-cyhalothrin + diflubenzuron X-cyhalothrin only

Mortality factor July August July August July August

Unknown 0.080 0.031 0.114 0.104 0.242 0.097
Parasitism 0.057 0.047 0.082 0.159 0.172 0.147
Disease 0.011 0.019 0.015 0.064 0.032 0.059
Predation 0.039 0.073 0.031 0.027 0.000 0.032

Indispensable mortality was calculated from larval death rates by subtracting the number entering the pupal stage when the mortality factor was
included from the number entering the pupal stage when the factor was not included.


DISCUSSION

This study demonstrated that, as Luck et al.
(1988) suggested, biases associated with the use
of a single natural enemy exclusion method can
be at least partially overcome by combining meth-
ods. For example, if our experiment had included
only exclusion cages (no X-cyhalothrin treatments),
effects of natural enemies would have been ap-
parent in August because of higher survival when
S. exigua were protected from natural enemies by
the cages (Fig 4C). In July, however, cage effects
also reduced S. exigua survival. Evidence in-
cluded greater mortality in partial exclusion
cages than in total exclusion cages, coupled with
similar survival in total exclusion cages and with
no predator exclusion (Fig. 4A). The insecticide
exclusion experiment showed that k-cyhalothrin
reduced predator populations and that S. exigua
was abundant in treated plots. However, this ex-
periment did not eliminate reduced parasitism or
disease incidence, trophobiosis or hormoligosis as
mechanisms of outbreak induction. Combining
cage exclusion with insecticide exclusion demon-
strated that, in plots treated with insecticides,
the increase in S. exigua populations resulted
from fewer natural enemies. Because rates of dis-
ease, parasitism and "unknown" mortality of col-
lected larvae were not different across insecticide
treatments, differences in S. exigua population
densities (Fig. 2) between insecticide treatments
could be attributed to differences in predation.
The death rate analyses for experimentally
manipulated populations effectively demon-
strated which mortality factors were important in
both insecticide-treated and untreated cotton.
This analysis also showed that different factors
were important for mortality in outbreak and
nonoutbreak populations.
Estimating predation rates based on exclusion
cages with the formula of Royama (1981), which
subtracts effects of parasitism from combined ef-
fects of parasitism and predation, suffers some of
the shortcomings of the common practice of as-
signing unexplained mortality to predation. If
rates of parasitism are low, as in 1989, estimates


of predation should be relatively accurate. In
1990, observed mortality due to parasitism of col-
lected larvae usually was at least equal to esti-
mates of mortality due to a combination of
parasitism and predation in exclusion cages.
Thus, if estimates of mortality due to combined
factors are accurate and parasitism is common,
predation may be seriously underestimated.
As in California cotton (Eveleens et al. 1973;
Hogg & Gutierrez 1980), when predator popula-
tions were not disrupted with insecticides, S. ex-
igua populations were held below outbreak
densities primarily by polyphagous predators. In
California, adult and immature Geocoris pallens
Stalh, Orius tristicolor (White), Nabis americof-
erus Carayon and immature C, .-..p- carnea
Stephens were important predators of S. exigua
eggs and newly closed larvae (Eveleens et al.
1973). Many of the same, or closely related spe-
cies, are common in Alabama cotton (Gaylor &
Gilliland 1976; Fleischer et al. 1985). Fire ants
also have been reported to be effective S. exigua
predators in Alabama (Cobb 1973). All of these
polyphagous predators, except adult Nabis spp.,
are capable of entering cages covered by the me-
dium mesh, and may have contributed to natural
control of S. exigua. However, only fire ants were
more abundant in plots with few S. exigua larvae
than in plots with dense larval populations. Thus,
circumstantial evidence indicates that fire ants
were key S. exigua predators in plots that were
not treated with k-cyhalothrin.
When populations of predators were not re-
duced by insecticides, as in 1990, the parasitoid,
C. marginiventris, was relatively unimportant as
a larval mortality agent. The species was impor-
tant in reducing populations of small and medium
S. exigua in both insecticide-treated and un-
treated plots in July 1990. Despite high levels of
parasitism by C. marginiventris in August 1990,
the parasitoid was not responsible for the sparse
S. exigua populations in cotton that had dense
predator populations. When predators were
present, they attacked both parasitized and un-
parasitized S. exigua, and little damage to cotton
occurred. Parasitism was insufficient to prevent


March 2001







Armyworn Symposium 2000: Stewart et al.


an economically damaging S. exigua population
from occurring in plots with few predators. De-
spite the presence of the parasitoid, defoliation of
cotton treated with X-cyhalothrin was severe in
August. Thus, the presence of a sufficient preda-
tor population was necessary to prevent an out-
break of S. exigua. This does not imply that
parasitoids were unimportant in regulating pop-
ulations of S. exigua. Our treatments did not af-
fect parasitoid attack rates. If parasitism had been
reduced by insecticide applications, we would
have expected to observe even more dramatic in-
creases in beet armyworm larval populations.
In California, egg predation (39%) also was im-
portant to S. exigua population regulation (Hogg
& Gutierrez 1980). We did not estimate egg mor-
tality, but it probably was not important in k-cyh-
alothrin-treated plots in 1990 because predator
populations were sparse. If 39% egg predation
were added to our death-rate analyses for plots
with predators, 1 for small larvae would be re-
duced to 610. However, indispensable mortality
for egg predation in plots with predators would be
only 0.007 for each cohort in control plots and
0.010 in combination plots in July 1990. In 1989,
IM for eggs would have been 0.103 and 0.003 for
July and August, respectively. Thus, 39% egg pre-
dation would have been important only in July
1989. Instead of determining which factors regu-
late densities of an entire host generation, pest
managers may want to know which mortality
agents in an agroecosystem reduce the pest popu-
lation density before it reaches a damaging stage
or before it enters sites where it is protected from
natural mortality agents or pesticides. Small and
medium size S. exigua cause less damage to cot-
ton than do large larvae. Therefore, a primary
objective of some cotton IPM programs is to estab-
lish conditions that favor mortality by natural en-
emies to S. exigua eggs and small and medium
size larvae, so that economically damaging num-
bers do not survive to the large size class.
Survival past the larval stage is important
only if survivors contribute to a subsequent gener-
ation that causes economic injury. Thus, mortality
to large larvae of the July S. exigua generation is
important only if survivors contribute substan-
tially to outbreaks in August. Mortality to pupae
could be important, but pupal mortality appar-
ently is negligible (Hogg & Gutierrez 1980). The
occurrence of each S. exigua generation is associ-
ated with peaks in adult flight activity (Trumble
& Baker 1984). The role of immigration in S. ex-
igua outbreaks in August is unknown but may be
important. Thus, the relative importance of the
July S. exigua generation and of immigration in
August to outbreaks in August is unclear.
The August S. exigua generation does not con-
tribute to subsequent damage to cotton. Most cot-
ton in Alabama is not susceptible to S. exigua
damage after August, and S. exigua apparently


does not readily overwinter in the state. Thus, nat-
ural mortality to early developmental stages of the
August generation should be more important to
the pest manager than is mortality to the entire
generation. Diseases of large larvae were most im-
portant in the decline of the S. exigua outbreak in
August 1989. However, natural mortality due to
predation on early developmental stages may have
been more important than mortality to later stages
if the goal was to avoid a damaging outbreak.
Unlike most population ecologists, pest man-
agers often are confronted with identifying natu-
ral control agents in an agroecosystem that has
been modified by insecticides. Despite the risks of
insecticide-induced outbreaks of S. exigua, pyre-
throids usually are applied in southern Alabama
cotton for control of Helicoverpa zea (Boddie) and
Heliothis virescens (F.). Consequently, the pest
manager also may want to know which mortality
factors might be manipulated to reduce the den-
sity of a pest population that has reached damag-
ing levels as a result of insecticide applications.
Adult and pupal C. marginiventris are susceptible
to pyrethroids (Ruberson et al. 1993), but during
1990, rates of parasitism by this species were not
different in treated and untreated cotton. When a
broad-spectrum insecticide must be applied to
control other pests, parasitism and disease may
be the most important natural mortality factors
remaining. If techniques can be developed for
augmenting populations of C. marginiventris or
diseases, these natural enemies might have po-
tential in applied biological control programs.
Levins & Wilson (1980) listed several reasons
for the lack of application of ecological theory to
agroecosystems. A primary reason for this situa-
tion is the different perspectives of the basic ecol-
ogist and the pest manager. However, questions of
interest to both the ecologist and the pest man-
ager can be addressed by combining experimental
methods that are commonly used in studying nat-
ural control in agroecosystems with death-rate
analyses or with life tables.

ACKNOWLEDGMENTS
The help of Larry Wells and other personnel at the
Wiregrass Substation of the Alabama Agricultural
Experiment Station is sincerely appreciated. We thank
M. E. Schauff, N. E. Woodley, R. W. Carlson, E. E. Gris-
sell and P. M. Marsh, USDA, Taxonomic Unit, Sys-
tematic Entomology Laboratory, Beltsville, MD for
identifying the parasitoids. This research was sup-
ported in part by the Alabama Cotton Commission. Pub-
lished as journal article PS9698 of the Mississippi
Agricultural and Forestry Experiment Station.

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Florida Entomologist 84(1)







Armyworm Symposium 2000: Lezama-Gutifrrez et al.


OCCURRENCE OF ENTOMOPATHOGENS OF SPODOPTERA FRUGIPERDA
(LEPIDOPTERA: NOCTUIDAE) IN THE MEXICAN STATES OF MICHOACAN,
COLIMA, JALISCO AND TAMAULIPAS

ROBERTO LEZAMA-GUTIERREZ', JOHN J. HAMM2, JAIME MOLINA-OCHOA1, MARILU LOPEZ-EDWARDS1,
ALFONSO PESCADOR-RUBIO3, MARTIN GONZALEZ-RAMIREZ1 AND ELOISE L. STYER4
1Facultad de Ciencias Biol6gicas y Agropecuarias, Universidad de Colima
Apartado Postal No. 36, Tecoman, Colima 28100, M6xico

2Crop Protection and Management Research Unit, USDA-ARS, PO Box 748, Tifton, GA 31793-0748

3Centro Universitario de Investigaci6n y Desarrollo Agropecuario, Universidad de Colima
Apartado Postal No. 36, Tecoman, Colima 28100, M6xico

4Diagnostic and Investigational Laboratory, The University of Georgia, PO Box 1389, Tifton, GA 31793-1389

ABSTRACT

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (FAW) larvae and soil samples were col-
lected from corn and sorghum fields in the Mexican states of Michoacan, Colima, and Jalisco
during August 1998. Additional FAW larvae were collected from a sorghum field in Tamauli-
pas, Mexico in September. A total of 2219 FAW larvae from 20 locations and 76 soil samples
from 19 locations were examined for indigenous FAW biological control agents. Four species
of entomopathogenic fungi representing two classes, Zygomycetes (Entomophthorales) and
Hyphomycetes (Beauveria bassiana, Nomuraea rileyi, and Hirsutella sp.) were recovered
from 43 (1.94%) of FAW larvae. An unidentified microsporidian was collected from 32
(1.44%) of FAW larvae, 29 from Colima, 2 from Jalisco, and 1 from Michoacan. Forty nine lar-
vae (2.21%) parasitized by mermithid nematodes were collected in the state of Colima. Two
(0.09%) larvae infected with ascovirus were collected in Tamaulipas. Three species of Hypho-
mycetes (Paecilomyces fumosoroesus, B. bassiana, and Metarhizium anisopliae) were iso-
lated from soil samples using Galleria mellonella larval traps. Entomopathogenic
nematodes (Steinernema sp. and Heterorhabditis sp.) were recovered from soil samples from
5 of 19 localities using Galleria mellonella larval traps. Bacillus thuringiensis was isolated
from soil samples from 12 locations. The most widely distributed microbial control agent on
FAW larvae in the Western Coast of Mexico was the fungus N. rileyi, and from soil were the
bacterium B. thuringiensis and steinernematid nematodes. The microsporidian was found
predominantly in Colima and the mermithid nematodes only in Colima. Thus, Colima had
the highest total percent mortality (9.67%) due to fungi, microsporidia and mermithids.

Key Words: Fall armyworm, biological control, maize, Nomuraea rileyi, mermithid nematode,
microsporidia

RESUME

Larvas de gusano cogollero, Spodoptera frugiperda (J. E. Smith) (FAW) y muestras de suelos
fueron colectadas de campos cultivados de maiz y sorgo, en los estados mexicanos de Mi-
choacan, Colima y Jalisco, durante Agosto de 1998. Mas larvas de FAW fueron colectadas de
sorgo en Tamaulipas, M6xico en Septiembre. Un total de 2219 larvas de FAW provenientes
de 20 localidades y 76 muestras de suelos de 19 localidades fueron examinadas en buisgueda
de agents locales de control biol6gico de FAW. Cuatro species de hongos entomopat6genos
de dos classes, Zygomycetes (Entomophthorales) e Hyphomycetes (Beauveria bassiana, No-
muraea rileyi, e Hirsutella sp.) fueron recuperados de 43 (1.94%) de las larvas. Un micros-
poridio no identificado fue colectado de 32 (1.44%) de las larvas, 29 de Colima, dos de Jalisco,
y uno de Michoacan. Cuarenta y nueve larvas (2.21%) parasitadas por nematodos mermiti-
dos fueron colectadas de Colima. Dos larvas (0.09%) infectadas con ascovirus fueron colecta-
das de Tamaulipas. Tres species de Hyphomycetes (Paecilomyces fumosoroseus, B.
bassiana, y Metarhizium anisopliae) se aislaron de muestras de suelos usando las trampas
de larvas de Galleria mellonella. Nematodos entomopat6genos (Steinernema sp. y Heteror-
habditis sp.) se recuperaron de muestras de suelos en 5 de 19 localidades usando las trampas
de larvas de G. mellonella. La bacteria Bacillus thruingiensis fue aislada de muestras de
suelos de 12 localidades. El agent de control microbiano mas ampliamente distribuido sobre
larvas de FAW en la Costa Occidental de M6xico fue el hongo N. rileyi y del suelo, B. thruin-
giensis y los nematodos entomopat6genos. El microsporidio fue encontrado predominante-







Florida Entomologist 84(1)


mente en Colima y los nematodos mermitidos s61o en Colima. Asi, Colima tuvo el prociento
de mortalidad mas alto (9.67%) debido a hongos, microsporidios y mermitidos.


Corn or maize, Zea mayz L., is one of the major
sources of animal and human foods in the Ameri-
cas and is one of the most valuable field crops in
the U.S.A. It is attacked by a variety of insect
pests including, one of the more destructive of
these pests, the fall armyworm (FAW),
Spodoptera frugiperda (J. E. Smith). The FAW
causes damage in all plant growth stages, often
limiting production due to severe damage to, or
complete destruction of, whorl-stage plants
(Wiseman et al. 1967, 1996). The use of microbial
control is a potentially valuable alternative to
chemical pesticides with their high cost, possible
pest resurgence, development of resistance, and
environmental contamination. The strategies for
using pathogens in biological control of insect
pests are determined primarily by the interac-
tions among pathogens, insect host, and environ-
ment, including the plant to be protected (Hamm
1984). Thus, a first step to develop a microbial
control program is the knowledge of the occur-
rence of insect pathogens, in order to utilize them
as a component of an integrated pest manage-
ment scheme.
The FAW is reported to be susceptible to vi-
ruses, fungi, protozoa, bacteria, and nematodes
(Steinhaus & Marsh 1962; Gardner & Fuxa 1980;
Fuxa 1982; Hughes et al. 1984; Agudelo-Silva
1986; Remillet & Silvain 1988; Richter & Fuxa
1990; Raulston et al. 1992; Molina-Ochoa et al.
1996), but their occurrence and distribution may
vary with their habitat. Geographical location
and agricultural practices, as well as pesticide
use, may have an impact on the occurrence of nat-
ural control agents in the host population or in
the soils (Fargues et al. 1992; Rogers & Marti
1992; Sosa-Gomez & Moscardi 1994; Vanninen
1996; Mietkiewski et al. 1997).
There is an increased interest in developing bio-
logical control methods for FAW in Mexico, but its
natural enemy complex (particularly pathogens)
is poorly known. More than three decades ago a
parasitic nematode (Mermithidae) was reported
to infest 21-53% of FAW larvae from Cotaxtla, Ve-
racruz, Mexico (Alcocer and M6ndez 1965). More
recently, Lezama-Gutierrez et al. (1996) assessed
the virulence of some isolates of Metarhizium
anisopliae (Metch.) Sor., Beauveria bassiana
(Bals.) Wuill., and Nomuraea rileyi (F.) Samson,
obtained from FAW larvae collected in the state of
Colima, Mexico, against eggs and neonates of
FAW. However, no detailed studies have been con-
ducted on the occurrence of FAW pathogens from
Colima, Michoacan, Jalisco, or Tamaulipas, Mex-
ico, although data from other countries suggest
that many entomopathogenic fungi and nema-
todes are ubiquitous inhabitants of the soil (Chan-


dler et al. 1997). This paper reports the natural
occurrence of entomopathogens and nematodes on
FAW larvae and in the soil of corn and grain sor-
ghum fields from the states of Colima, Jalisco,
Michoacan, and Tamaulipas, Mexico.

MATERIALS AND METHODS
Isolation of Pathogens from FAW Larvae

During August of 1998 collections of FAW lar-
vae were made from whorl-stage corn and grain
sorghum fields in the states of Colima, Jalisco,
and Michoacan, and 1 collection from fruiting
corn in Jalisco. A single collection of FAW larvae
was made from whorl-stage grain sorghum in
Tamaulipas in September. Concurrently, four soil
samples were obtained from each location in the
first three states. Locations 12 and 18 comprise
combinations of collections from adjacent fields of
whorl-stage maize and sorghum. Sample size
ranged from 25 to 300 FAW larvae per field. The
number collected is corrected by subtracting the
number that died from injury or unknown causes
during the first days after collection. Collection
data and percent infection by pathogens and nem-
atodes is presented in Table 1. Larval mortality
due to insect parasitoids is reported elsewhere
(Molina-Ochoa et al., in press).
The larvae were placed individually in 30 cc
plastic cups with pinto bean diet (Burton & Per-
kins 1989) and held in the laboratory to record
the larvae infected by entomopathogens and
mermithid nematodes. Mermithid nematodes
that emerged from larvae were collected and
placed in 70% alcohol. Larvae showing signs of vi-
rus infection or infection by microsporida were ex-
amined microscopically for occlusion bodies or
spores. Microsporidian and virus infected tissues
from field-collected insects were fixed in a modi-
fied Karnovsky's fixative, postfixed in OsO4, and
embedded in epoxy resin; sections were cut,
stained and examined as described by Styer et al.
(1987). The ascovirus was examined by negative-
stain electron microscopy using methods de-
scribed by Hamm et al. (1992). Ascovirus was di-
agnosed by the presence of vesicles in stunted
larvae and transmitted to other larvae using a
cactus spine (Hamm et al. 1986). Final identifica-
tion was made by electron microscopy (Federici et
al. 1991).
Dead larvae showing signs of fungus infection
were placed in a plastic Petri dish (60 x 10 mm)
lined with filter paper moistened with sterile dis-
tilled water, until the fungus sporulated on the in-
sect surface. Nomuraea rileyi was isolated from
dead larvae on medium composed of 200 ml of


March 2001







Armyworm Symposium 2000: Lezama-Guti6rrez et al.


TABLE 1. LOCATION, DATE, CROP, SAMPLE SIZE, AND TOTAL PERCENTAGE FALL ARMYWORM LARVAE INFECTED BY
PATHOGENS AND MERMITHID NEMATODES COLLECTED FROM CORN (C) OR SORGHUM (S) IN THE MEXICAN
STATES OF MICHOACAN (M), COLIMA (C), JALISCO (J), AND TAMAULIPAS (T).

Percentage
Code Location Date Crop No. coll. infected

M 1 Jazmin 08/07/98 C 25 8.0
M 2 El Batillero 08/07/98 C 26 0.0
M 3 La Sidra 08/07/98 C 84 2.4
M 4 La Sidra 08/08/98 C 89 9.0
M 5 El Hueso 08/08/98 C 102 2.0
M 6 Carreras 08/08/98 C 109 0.9
C 7 Mezcales 08/12/98 C 143 3.5
C 8 Los Clomos 08/12/98 C 84 14.3
C 9 Cerro Colorado 08/13/98 C 121 9.2
C 10 El Bordo 08/13/98 C 114 17.5
C 11 Crucero de Tepames 08/13/98 C 89 10.1
C 12 Pena Blanca 08/13/98 C & S 219 13.2
C 13 El Narajito 08/14/98 C 171 6.4
J 14 Los Pozos 08/19/98 S 81 7.4
J 15 Apastepe 08/19/98 C 89 4.5
J 16 Los Depositos 08/19/98 C 89 3.4
J 17 Sayula 08/19/98 C 89 9.0
J 18 Sayula 08/20/98 C & S 177 4.5
J 19 Sayula 08/20/98 C (ears) 18 16.7
T 20 El Mante 09/22/98 S 300 0.3


"V8" vegetable juice, 3 g CaCO3, 5 g glucose, 2 g
yeast extract, 15 g agar, and 800 ml distilled wa-
ter (Fargues & Rodriguez-Rueda 1980). Other
fungal species were grown on Sabouraud-Dex-
trose agar enriched with 1% (w/v) yeast extract
(SDAY), with 500 ppm chloramphenicol (Lezama-
Gutierrez et al. 1996) except the entomophtho-
rales which were not isolated.

Isolation of Entomopathogens from Soil
Four soil samples, from corn or sorghum fields,
were collected from each of 19 locations from the
states of Michoacan, Colima, and Jalisco. In every
location approximately 2 kg of soil was collected
from four points a few meters apart by digging to
a depth of 10-15 cm with a small spade. These sub-
samples were combined to form a sample. The soil
samples were put in plastic bags and taken to the
laboratory and stored at 25C until processing.
The storage time ranged from a few days to three
weeks. For processing, the soil was thoroughly
mixed and passed through a 0.4 mm mesh sieve to
break or separate any coarse lumps of soil or litter.
In order to isolate the entomopathogenic fungi
or nematodes, larvae of laboratory-reared Galle-
ria mellonella (L.) were used as bait (Chandler et
al. 1997; Bedding and Akhurst 1975). Four groups
of sieved soil from each location were placed in
plastic pots and five last instar bait larvae were
released into each pot. Pots were incubated at
room temperature (25C) in the dark for 10 days
(Zimmermann 1986; Woodring & Kaya 1988).


Dead, intact larvae were removed and surface-
sterilized in 1% sodium hypochlorite for 3 min,
then washed three times in sterile distilled water
and placed on damp filter paper within a sealed
Petri dish 5.5 cm diameter, and incubated at 25C
for 12 days (Chandler et al. 1997). Entomopatho-
genic fungi were isolated from the bait larvae us-
ing SDAY, with 500 ppm of chloramphenicol
(Lezama-Gutierrez et al. 1996). The fungi were
identified by microscopic inspection of morpholog-
ical characteristics in situ or after isolation in
SDAY, according to the criteria by Brady (1979)
and Samson et al. (1988). Nematodes were sepa-
rated to genera by identifying coloration of dead
bait larvae according to Woodring and Kaya (1988).
To isolate Bacillus thuringiensis Berliner from
the soil, 1 g samples from each location were
placed in 50 ml of sterile distilled water in bioas-
say tubes, mixed for 3 min, and heated to 80'C for
10 min. After heating, 100 gl, of each sample, was
placed on nutrient agar in four Petri dishes. Petri
dishes were incubated at 30C for 72 h, and colo-
nies were microscopically examined after fixation
and staining with methylene blue cotton. The
presence of protein crystals was utilized as iden-
tification criteria ofB. thuringiensis, according to
Chaufaux et al. (1997).

RESULTS
Out of 2219 FAW larvae collected from 20 loca-
tions, the percentage infected by pathogens and
mermithid nematodes ranged from 0 to 17.5 (Table







Florida Entomologist 84(1)


1), 77 larvae (3.47%) were killed by pathogens and
49 (2.21%) by mermithid nematodes. Four species
of entomopathogenic fungi, represented by three
Hyphomycetes, Beauveria bassiana (Bals.) Vuill.,
Nomuraea rileyi (F.) Samson, and Hirsutella sp.,
and one Zygomycete, Entomophthorales, were re-
covered (Table 2). Nomuraea rileyi was the most
abundant and widely distributed fungus attack-
ing FAW larvae in the three Western Mexican
States and accounted for most of the pathogen-
induced mortality of FAW larvae collected in
Michoacan and Jalisco (Table 2). Two larvae in-
fected with B. bassiana and a single larva infected
by a member of the Entomophthorales were col-
lected in Jalisco. A single larva infected with Hir-
sutella sp. was collected from Colima.
Mermithid infected FAW larvae were found only
in the state of Colima and were more numerous
than fungus infected larvae at 3 of the 7 locations.
Microsporida infected larvae were found pre-
dominately in Colima and were more numerous
than fungus infected larvae at 4 of the 7 locations
in Colima (Table 2). Collections from Michoacin
and Jalisco had 1 and 2 microsporida infected lar-
vae, respectively. All mortality appeared to be due
to the same unidentified microsporidian which
formed clumps of numerous thick-walled spores
with no apparent sporophorous vesicle (Fig. 1A).
The infected larvae showed no obvious symptoms
prior to death, but after death were often dry and
fragile, resembling the ash of a cigarette.


Four of five collections with rates of infection
greater than ten percent were from the state of
Colima (Table 1) and can be attributed to the
higher rates of infection by mermithid nematodes
and microsporidia in Colima than in the other
states (Table 2). The only other collection with
more than ten percent infection (J19) was a small
collection of larvae from ears of corn in Jalisco
which was entirely due to Nomuraea rileyi.
Two ascovirus infected larvae from Tamauli-
pas were the only virus infected larvae identified.
The ascovirus (Fig. 1 B & C) resembled the ascovi-
rus collected from FAW in Georgia and Florida,
forming vesicles in the fat body but not in the epi-
dermis or tracheal epithelium (Hamm et al. 1998).

Entomopathogens from Soil

The most numerous and widely distributed en-
tomopathogen isolated from soil samples was B.
thuringiensis which was isolated from 4 of 6 loca-
tions in Michoacan, 7 of 7 locations in Colima and
1 of 6 locations in Jalisco.
Three species of entomopathogenic fungi were
recovered from soil samples. Metarhizium ani-
sopliae was recovered from 5 locations, 2 of 7 from
Colima and 3 of 6 from Jalisco. Beauveria bassiana
was recovered from 4 locations, 1 from Michoacan,
1 from Colima, and 2 from Jalisco. Paecilomyces
fumosoroseus was recovered from a single soil
sample from Colima.


TABLE 2. PERCENTAGE OF FALL ARMYWORM LARVAE INFECTED BY VARIOUS PATHOGENS AT EACH LOCATION.

Code* N. r. Ent. Hir. B. b. Mer. Mic. Asc.

Ml1 8.0 0 0 0 0 0 0
M2 0 0 0 0 0 0 0
M 3 2.4 0 0 0 0 0 0
M4 9.0 0 0 0 0 0 0
M 5 1.0 0 0 0 0 1.0 0
M6 0.9 0 0 0 0 0 0
C 7 2.1 0 0 0 1.4 0 0
C 8 9.5 0 0 0 2.4 2.4 0
C 9 0.8 0 0 0 4.1 4.1 0
C 10 0 0 0 0 14.9 2.6 0
C 11 0 0 0 0 0 10.1 0
C 12 1.4 0 0 0 9.1 2.7 0
C 13 1.8 0 0.6 0 1.8 2.3 0
J 14 6.2 0 0 1.2 0 0 0
J 15 3.4 0 0 0 0 1.1 0
J 16 2.2 0 0 0 0 1.1 0
J 17 6.7 1.1 0 1.1 0 0 0
J 18 4.5 0 0 0 0 0 0
J 19 16.7 0 0 0 0 0 0
T 20 0 0 0 0 0 0 0.7

*Locations are described in Table 1.
N. r. = Nomuraea rleyi,Ent. = Entomophthora sp., Hi = Hirsutella sp.,B. b. = Beauveria bassiana, Mer. = Mermithid nematode, Mic. = Microsporidia,
Asc. = Ascovirus.


March 2001







Armyworm Symposium 2000: Lezama-Gutierrez et al.


Fig. 1. A) Cluster of microsporidia spores from fall armyworm larva collected in Colima, Mexico, 6,200x, arrows
pointing to nuclei. B & C) Ascovirus from fall armyworm larva collected in Tamaulipas, Mexico: B, Enlargement of
viral inclusion body showing unenveloped virus (arrowhead) and enveloped virions 58,000x. C, negative stain of vir-
ion showing characteristic surface of envelop 150,000x.







Florida Entomologist 84(1)


Two genera of entomogenous nematodes were
collected from soil samples. Steinernematid nema-
todes were collected from 3 of 4 locations in Micho-
acan and 1 location in Colima; heterorhabditid
nematodes were collected from only one location
in Colima.

DISCUSSION
Nomuraea rileyi is recognized as an important
pathogen of many insect pests, especially lepi-
dopteran larvae (Ignoffo 1981; Carruthers &
Soper 1987), and has been reported infecting
FAW in Puerto Rico, Colombia, Honduras, Mex-
ico, and U.S.A. (Gardner & Fuxa 1980; Ignoffo
1981; Wheeler et al. 1989; Sanchez-Pena 1990;
Pantoja & Fuxa 1992). Entomophthora aulicae
was reported infecting FAW and other noctuid
larvae in sorghum in Georgia (Hamm 1980).
Erynia radicans was reported infecting FAW in
Venezuela (Agudelo-Silva 1986).
Spodoptera frugiperda (= Laphygma fru-
giperda) has been reported to be infected by
Nosema laphygmae Weiser, Nosema trichoplusiae
Tanabe and Tamashiro and Vairimorpha necatrix
(Kramer) (Bulla & Cheng 1977; Gardner & Fuxa
1980). Nosema laphygmae was described from
larvae, pupae and adults from the vicinity of Car-
acas, Venezuela (Weiser 1959). Vairimorpha neca-
trix was reported naturally infecting FAW by
Patel and Habib (1988). Nosema trichoplusiae
was demonstrated to infect FAW in the labora-
tory. Unidentified microsporidia were reported
from FAW in Louisiana by Fuxa (1982), in Vene-
zuela by Agudelo-Silva (1986), and in Puerto Rico
by Pantoja & Fuxa (1992). We did not findNosema
or Vairimorpha in our collections; the unidenti-
fied microsporidian that we found was obviously
not in either of those genera based on the ar-
rangement of spores. We were unable to infect
FAW larvae using dried spores that were a few
weeks old and thus were unable to study the de-
velopmental stages of the microsporidian.
The ascovirus isolated from FAW larvae col-
lected in Tamaulipas is the first report of an as-
covirus from Mexico. While the ascovirus can
cause significant mortality in FAW (Hamm et al.
1986) it interferes with development of braconid
parasitoids (Hamm et al. 1985). Although bacu-
loviruses, nuclear polyhedrosis virus and granu-
losis virus, have been reported infecting FAW in
many areas, they were not found in this survey.
Fuxa (1982) reported that in Louisiana, NPV was
more prevalent in fall armyworms infesting pas-
tures than in those infesting corn or sorghum un-
til mid July or early August, but the eventual
infection rates were similar. He suggested that
the lag in virus in corn and sorghum could be be-
cause rain and other physical agents cannot move
the NPV from the soil reservoir to vegetation as
easily as in grass. Also, the faster growth of corn


or sorghum may produce more uncontaminated
leaf surface and larvae may not move from plant
to plant as readily as in pastures.
Mermithid nematodes have been reported in-
fecting FAW in various parts of its range but have
not been studied extensively. Valincente (1986) re-
ported FAW attacked by mermithid nematodes in
Brazil. Pair et al. (1986) reported an unidentified
mermithid attacking FAW in South Carolina.
Wheeler et al. (1989) reported Hexamermis sp. from
FAW in Honduras where it made up 23% of the nat-
ural enemy complex of FAW on corn. Hexamermis
has been reported to cause 8-100% FAW mortality
in Mexico (Alcocer & M6ndez 1965) and over 50%
FAW mortality in Nicaragua (Van Huis 1981).
Steinernema riobravis is an important control
agent for prepupae and pupae of FAW and corn
earworm, Helicoverpa zea (Boddie), in cornfields
of the Lower Rio Grande Valley (Raulston et al.
1992; Cabanillas et al. 1994) where the nematode
appears to be naturally selected for the subtropi-
cal semi-arid environment.
The distribution of the various entomopatho-
gens indicates a potential for increasing biological
control by moving some of the pathogens and nem-
atodes from one area to another. Additional re-
search is needed on the identification and biology
of the microsporidian and the mermithid nema-
tode to determine their potential for biological
control. Also, additional research is needed to
determine the species and strains of the ento-
mopathogenic nematodes, Steinernematidae and
Heterorhabditidae, isolated from the soil and their
potential for biological control of fall armyworm.

ACKNOWLEDGMENTS

This project was supported in part by Specific Coop-
erative Agreement #58-6602-7-F101 between the United
States Department of Agriculture, Agricultural Re-
search Service and the Universidad de Colima, Mexico.

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Florida Entomologist 84(1)







Armyworm Symposium 2000: Molina-Ochoa et al.


A SURVEY OF FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE)
PARASITOIDS IN THE MEXICAN STATES OF MICHOACAN,
COLIMA, JALISCO, AND TAMAULIPAS

JAIME MOLINA-OCHOA', JOHN J. HAMM2, ROBERTO LEZAMA-GUTIERREZ', MARILU LOPEZ-EDWARDS1,
MARTIN GONZALEZ-RAMIREZ1 AND ALFONSO PESCADOR-RUBIO3
1Facultad de Ciencias Biol6gicas y Agropecuarias, Universidad de Colima,
Apartado Postal No.36, Tecoman, Colima 28100, M6xico

2Crop Protection and Management Research Unit, USDA-ARS, P. 0. Box 748, Tifton GA 31274 0748

3Centro Universitario de Investigaci6n y Desarrollo Agropecuario, Universidad de Colima,
Apartado Postal No.36, Tecoman, Colima 28100, M6xico

ABSTRACT

Fall armyworm larvae, Spodoptera frugiperda (J. E. Smith) were collected from whorl stage
corn or sorghum in the states of Michoacan, Colima, and Jalisco in August, and Tamaulipas,
Mexico in September 1998. Eleven species of hymenopteran parasitoids were recovered rep-
resenting 3 families: Ichneumonidae (Ophion flavidus Brulle, Campoletis flavicincta Ash-
mead, and Pristomerus spinator F.); Braconidae (Aleiodes laphygmae Viereck, Cotesia
marginiventris Cresson, Meteorus laphygmae Viereck, Meteorus sp., Chelonus insularis
Cresson, Chelonus sp. probably cautus Cresson, and Chelonus sp.); and Eulophidae (Euplec-
trus platyhypenae Howard). The overall rate of parasitism was 11.3%, based on 2219 larvae
collected. The highest rate of parasitism from a single collection was 26.5%, representing 6
species of parasitoids in Michoacan. The next highest rate of parasitism, 23%, was by a sin-
gle species, C. flavicincta, in Michoacan. The most widely distributed species was P. spinator,
occurring in 12 collections from 3 states. Chelonus sp. was collected from all four states in
only 6 collections. The greater diversity of parasitoids and higher rates of parasitism in Mi-
choacan may be related to the more diverse habitat with more forests, orchards, and pas-
tures near the cornfields in that state.

Key Words: parasitoids, Spodoptera frugiperda, Ophion, Campoletis, Pristomerus, Aleiodes,
Cotesia, Meteorus, Chelonus, Euplectrus, maize, corn, sorghum, Mexico

RESUME

Larvas de gusano cogollero, Spodoptera frugiperda (J. E. Smith) fueron colectadas de maiz
y sorgo para grano en etapa de verticilio en los estados de Michoacan, Colima y Jalisco du-
rante Agosto, y en Tamaulipas, M6xico durante Septiembre de 1998. Once species de para-
sitoides himen6pteros se recuperaron y representaron a 3 families: Ichneumonidae (Opion
flavidus Brulle, Campoletis flavicincta Ashmed, y Pristomerus spinator F.); Braconidae
(Aleiodes laphygmae Viereck, Meteorus sp., Chelonus insularis Cresson, Chelonus sp. proba-
blemente cautus Cesson, y Chelonus sp.); y Eulophidae (Euplectrus platyhypenae Howard).
La proporci6n general de parasitismo fue de 11.3%, basada en 2219 larvas colectadas. La
proporci6n mas alta de parasitismo proveniente de una colecta simple fue de 26.5%, repre-
sentando 6 species de parasitoides en Michoacan. La siguiente proporci6n mas alta, 23%,
fue para una especie simple, C. flavicincta, en Michoacan. La especie distribuida mas am-
pliamente fue P. spinator, presentandose en 12 colectas hechas en 3 estados. Chelonus sp. se
colect6 en los cuatro estados s6lo en 6 colectas. La diversidad mas grande de parasitoides y
proporciones mas altas de parasitismo en Michoacan pueden estar relacionadas con los ha-
bitat mas diversos con mas bosques, huertas y pastizales cerca de los maizales en ese estado.


The fall armyworm, Spodoptera frugiperda (J. wintering habitats each year (Luginbill 1928).
E. Smith), is an important economic pest of corn, The seasonal migration of fall armyworm from
sorghum, grasses, and occasionally other crops in Southern Florida and the Lower Rio Grande Val-
North America, Central America and parts of ley has been studied by Westbrook and Sparks
South America (Luginbill 1928; Vickery 1929; (1986), Pair et al. (1986, 1991), and Pair & West-
Mitchell 1979; Andrews 1980, 1988). The fall ar- brook (1995). The potential for migration from
myworm lacks the ability to diapause during cold other areas along the Mexican Gulf Coast was
weather and thus spreads northward from over- discussed by Raulston et al. (1986).







Florida Entomologist 84(1)


Early workers recognized the value of parasi-
toids in reducing larval populations of fall army-
worm (Luginbill 1928; Vickery 1929). Andrews
(1988) reviewed the Latin American research on
fall armyworm including its parasitoids, and Ash-
ley et al. (1989) reviewed the literature on fall
armyworm. Biological control of this pest is desir-
able because of increasing economic and environ-
mental concerns which have resulted in surveys
of parasitoids and other natural enemies in differ-
ent parts of its range (Hogg et al. 1982; Pair et al.
1986; Gross & Pair 1986; Castro & Pitre 1989).
Ashley (1979) listed 53 species of fall armyworm
parasitoids from 43 genera and 10 families and
suggested that importations from Central and
South America into Florida and Texas may signif-
icantly reduce overwintering populations. He also
suggested that the number of parasitoids unique
to either North or South America is indicative of
the need for more larval collections so as to estab-
lish whether differences actually are present or
are simply a function of inadequate records. Ash-
ley (1986) reported the highest parasitism levels
of fall armyworm were found for corn and that
Chelonus insularis Cresson had the highest para-
sitism rates of all the parasitoids for North and
Central America. Pair et al. (1986) found that the
highest rates of parasitism were in overwintering
areas of Mexico-Texas and south Florida and con-
firmed that C. insularis was the most common
parasitoid. They presented evidence for differen-
tial distribution of some parasitoids as indicated
by their native scarcity or abundance in defined


geographical areas. Riggin et al. (1993) concluded
that the most efficient biological control programs
for fall armyworm will be ones that use and am-
plify several parasitoid species rather than pro-
grams that rely on an individual natural enemy.
Biological differences (developmental rates,
reproductive compatibility and susceptibility to
insecticides) between populations of fall army-
worm collected from corn in different areas of
Mexico suggested some geographical isolation of
populations (Lopez-Edwards et al. 1999). There-
fore, we surveyed the natural enemies of fall ar-
myworm in west-central and northeastern
Mexico in an effort to find new parasitoids and to
add to the knowledge of the distribution of known
parasitoids of this pest.

MATERIALS AND METHODS

During August 1998, collections of fall army-
worm larvae were made from whorl-stage corn
and sorghum in the states of Michoacan, Colima,
and Jalisco, and 1 collection was made from fruit-
ing corn in Jalisco. A later collection was made
from whorl-stage sorghum in Tamaulipas in Sep-
tember. No efforts were made to collect eggs or pu-
pae. The larvae were placed individually in 30 cc
plastic cups with pinto bean diet (Burton 1969)
and held in the laboratory for emergence of para-
sitoids. Adult parasitoids were submitted to the
USDA Systematic Entomology Laboratory, Belts-
ville, MD for identification. The dates and loca-
tions of collections are presented in Table 1.


TABLE 1. LOCATION, DATE, CROP, SAMPLE SIZE, AND TOTAL PERCENTAGE FALL ARMYWORM LARVAE PARASITIZED BY HY-
MENOPTERA, COLLECTED FROM CORN (C) OR SORGHUM (S) IN THE MEXICAN STATES OF MICHOACAN (M),
COLIMA (C), JALISCO (J), AND TAMAULIPAS (T).

Code Location Date Crop No. coll. Percentage parasitized

M 1 Jazmin 08/07/98 C 25 4.0
M 2 El Batillero 08/07/98 C 26 23.0
M 3 La Sidra 08/07/98 C 84 6.0
M 4 La Sidra 08/08/98 C 89 9.0
M 5 El Hueso 08/08/98 C 102 26.5
M 6 Carreras 08/08/98 C 109 14.7
C 7 Mezcales 08/12/98 C 143 7.0
C 8 Los Clomos 08/12/98 C 84 2.4
C 9 Cerro Colorado 08/13/98 C 121 3.3
C 10 El Bordo 08/13/98 C 114 11.4
C 11 Crucero de Tapames 08/13/98 C 89 0
C 12 Pena Blanca 08/13/98 C&S 219 15.5
C 13 ElNarajito 08/14/98 C 171 7.6
J 14 Los Pozos 08/19/98 C 81 8.6
J 15 Apastepe 08/19/98 C 89 7.9
J 16 Los Depositos 08/19/98 C 89 4.5
J 17 Sayula 08/19/98 C 89 2.2
J 18 Sayula 08/20/98 C & S 177 18.6
J 19 Sayula 08/20/98 C (ears) 18 0
T 20 ElMante 09/22/98 C 300 19.7


March 2001







Armyworm Symposium 2000: Molina-Ochoa et al.


Collection size ranged from 25 to 300 fall army-
worm larvae. Collections 12 and 18 comprise com-
binations of samples from adjacent fields of
whorl-stage corn and sorghum. The number col-
lected was corrected by subtracting the number
that died from injury or unknown causes during
the first few days after collection before calculat-
ing percent parasitism. Mortality due to patho-
gens and nematodes will be reported elsewhere.

RESULTS AND DISCUSSION

Out of 2219 fall armyworm larvae collected,
251 produced parasitoids, for a parasitism rate of
11.3%. This represented 11 species from 3 fami-
lies of Hymenoptera: 7 Braconidae, 3 Ichneu-
monidae, and 1 Eulophidae. Only 2 of 20
collections produced no parasitoids: a collection
from whorl-stage corn at C11 in Colima and a col-
lection from ears of corn at J19 in Jalisco. The two
highest rates of parasitism were found in Micho-
acan at M5 and M2 with 26.5 and 23% parasit-
ism, respectively (Table 1). M5, C12, and C13, had
the highest number of parasitoid species, 6 (Ta-
bles 2 and 3). In contrast, M2 had only a single
species of parasitoid and represented the highest
rate of parasitism by a particular species, 23%.
The next most diverse collections of parasitoids
were from M3 and M6 in Michoacan with 5 spe-
cies each (Tables 2 and 3).


Pristomerus spinator F. was the most widely
distributed parasitoid, being found in 12 collec-
tions from 3 states (Table 3). At nearly 13%, it
showed the second highest rate of parasitism. P.
spinator was listed as a parasite of fall armyworm
from Nicaragua, Brazil, and Cuba by Andrews
(1988). P. spinator was reported from Quintana
Roo and Tamaulipas, M6xico, by Carrillo (1980)
and Pair et al. (1986) respectively. While this was
the most widely distributed parasitoid in our col-
lections, we did not find it in the single collection
from Tamaulipas.
Campoletis flavicincta Ashmead was found in
8 collections from 2 states, occurring most abun-
dantly in Michoacan in 5 of 6 collections and also
had the highest rate of parasitism, 23% (Table 3).
However, it was not found in collections from
Colima and Tamaulipas. C. flavicincta was listed
from several states of the U.S.A. and from Uru-
guay by Ashley (1979), and from Nicaragua, Uru-
guay, and Brazil by Andrews (1988).
Ophion flavidus Brulle was found in one collec-
tion in Michoacan and two collections from
Colima, with the highest rate of parasitism (5%)
in Colima. 0. flavidus was listed from the U.S.A.
by Ashley (1986) and from Honduras and Brazil
by Andrews (1988).
Chelonus insularis was found in 9 collections
from 3 states but always at less than 5%. Lugin-
bill (1928) and Vickery (1929) indicated that C. in-


TABLE 2. PERCENTAGE OF FALL ARMYWORM LARVAE PARASITIZED BY EACH SPECIES OF BRACONIDAE AT EACH LOCATION.

Braconidae

Code* A. 1. C. i. C. c. C. sp. C. m. M. 1. M. sp.

M1 0 0 0 0 0 0 0
M2 0 0 0 0 0 0 0
M3 0 0 0 0 0 0 1.2
M 4 0 0 0 2.2 0 0 3.4
M 5 0 1.0 1.0 0 2.0 0 2.9
M 6 0 0.9 2.8 0 0 0 0
C 7 0 2.1 3.5 0 0 0.7 0
C 8 0 0 0 1.2 1.2 0 0
C 9 0 0.8 0 0 0 0 0
C 10 0 0.9 3.5 0 0.9 0 0
C11 0 0 0 0 0 0 0
C 12 0 0 10.6 2.9 0 1.9 1.0
C 13 0 2.3 0.6 1.2 0 0.6 0
J 14 0 3.7 0 0 0 0 0
J 15 0 0 0 0 0 0 6.7
J 16 0 1.1 0 0 0 0 3.4
J 17 0 2.2 0 0 0 0 0
J 18 0 1.1 0 9.6 0 0 0
J19 0 0 0 0 0 0 0
T 20 0.3 0 0 0.7 0 10.3 0


*Locations are described in Table 1. A. 1. = Aleoides laphygmae,
C. m. = Cotesta marginiventris, M. 1. = Meteorus laphygmae.


C. i. = Chelonus insularns, C. c. = Chelonus sp. prob. cautus, C. sp. = Chelonus sp.,







Florida Entomologist 84(1)


TABLE 3. PERCENTAGE OF FALL ARMYWORM LARVAE PARASITIZED BY EACH SPECIES OF ICHNEUMONIDAE AND EU-
LOPHIDAE AT EACH LOCATION.

Ichneumonidae Eulophidae

Code* C.f. O.f. P.s. E.p.

M 1 0 0 4.0 0
M 2 23.1 0 0 0
M 3 1.2 1.2 1.2 1.2
M 4 1.1 0 2.2 0
M 5 6.9 0 12.7 0
M 6 1.8 0 8.2 0.9
C 7 0 0 0.7 0
C8 0 0 0 0
C 9 0 0 1.7 0
C 10 0 0 6.1 0
C 11 0 0 0 0
C 12 0 4.8 8.7 0
C 13 0 0.6 2.3 0
J 14 1.2 0 3.7 0
J 15 1.1 0 0 0
J 16 0 0 0 0
J 17 0 0 0 0
J 18 2.3 0 4.5 0
J19 0 0 0 0
T 20 0 0 0 8.3

*Locations are described in Table 1. C. f = Campoletts flavicmcta, O. f = Ophion flavdus,P. s. = Prstomerus spnator,E. p. = Euplectrus platyhypenae.


sularis was important in controlling fall army-
worm populations in its overwintering habitats of
Florida and Southern Texas. Pair et al. (1986)
confirmed the importance of C. insularis in these
areas but found that it was of secondary impor-
tance elsewhere. C. insularis has been reported as
an important parasite of fall armyworm in Latin
America (Andrews 1988). Ashley (1986) reported
that the Braconidae had the greatest impact on
fall armyworm populations with C. insularis hav-
ing the highest parasitism rates in Central and
North America.
Chelonus sp. was found in 6 collections, repre-
senting all 4 states, and Chelonus sp. probably
cautus was found in 6 collections, representing
only 2 states (Table 2). The taxonomy of the genus
Chelonus needs more study in Mexico (P. M. Marsh,
pers. comm.). In our collections, C. insularis was
most common in Colima and was not found in the
single collection from Tamaulipas. When all Che-
lonus sp. are considered, they were found in 14 lo-
cations, representing all 4 states. While most of
the collections had less than 5% parasitism by
any member of the genus Chelonus, one collection
in Colima had 11% parasitism by Chelonus sp.
probably cautus and one collection from Jalisco
had 10% parasitism by Chelonus sp. Thus, Chelo-
nus spp. appear to be highly important as natural
enemies of fall armyworm in Mexico.
Meteorus laphygmae Viereck was found in 4
collections, representing 2 states. It occurred at


only 1 to 2% in the three collections in Colima, but
was the most abundant in Tamaulipas with 10%.
Meteorus sp. was found in 6 collections, represent-
ing 3 states, with its highest rate of 7% in Jalisco.
Ashley (1986) listed the genus Meteorus only from
the continental U.S.A., stating thatM. laphygmae
in Texas had its greatest impact on fall army-
worm feeding on grass. Andrews (1988) lists M.
laphygmae from Surinam, Venezuela, and Colom-
bia. Pair et al. (1986) list Meteorus autographae
Musebeck from Mexico as well as several south-
ern states of the U.S.A.
Aleiodes laphygmae Viereck (formerly Rogas
laphygmae) was the only parasitoid limited to a
single collection, in Tamaulipas. Ashley (1986) re-
ported that R. laphygmae appeared to be confined
to the continental U. S. and that the highest par-
asitism rates occurred in fall armyworm feeding
on grass. Andrews (1988) listed R. laphygmae
from Nicaragua.
Cotesia marginiventris Cresson (formerly Ap-
anteles marginiventris) was found in 4 collections,
representing only 2 states at rates of 2% or lower.
C. marginiventris has often been reported as a
parasitoid of fall armyworm in the U.S.A. (Ashley
1986). Andrews (1988) listed A. marginiventris
from Lesser Antilles, Surinam, Venezuela, Brazil,
and Nicaragua. Ashley (1986) reported that C.
marginiventris appeared to have its greatest im-
pact on fall armyworm feeding on grass. However,
under experimental conditions of whorl-stage corn


March 2001







Armyworm Symposium 2000: Molina-Ochoa et al.


infested with newly hatched fall armyworm, C.
marginiventris can produce rates of parasitism
up to 40% in Georgia (Hamm et al. 1994).
Euplectrus platyhypenae Howard was the only
member of the family Eulophidae collected. E.
platyhypenae was most abundant in Tamaulipas
(8%), but occurred at very low levels in 2 collec-
tions from Michoacan. Ashley (1986) lists E.
platyhypenae from Lesser Antilles, Cuba, Barba-
dos, Trinidad, Venezuela, and Colombia. Mon-
toya-Burgos (1980) reported natural parasitism
by Euplectrus sp. against second instar fall army-
worm of about 15% in corn from Veracruz.
Due to technological advances in mass rearing,
Lewis and Nordlund (1980) suggested C. insu-
laris and C. marginiventris as candidates for
"rear and release" approaches using either: (1) re-
lease throughout the overwintering zone, (2)
early-season colonization, or (3) therapeutic re-
lease on target crops.
We did not sample eggs or pupae and therefore
did not find any egg (except for Chelonus which is
an egg-larval parasitoid) or pupal parasitoids.
The rare incidence of tachinid parasitoids was
probably due to the low incidence of large host
larvae in our collections (Rohlfs & Mack 1985).
Archytas marmoratus (Townsend) is an impor-
tant parasitoid of both fall armyworm and corn
earworm, Helicoverpa zea (Boddie), in whorl-
stage corn in the U.S.A (Gross & Pair 1991). Pair
et al. (1986) reported thatA. marmoratus was the
primary parasitoid attacking medium and large
fall armyworm larvae in whorl-stage corn
throughout the southern states during the spring
of 1981-83.Archytas spp. have been reported at-
tacking S. frugiperda in several areas in Latin
America (Andrews 1988). The low incidence of O.
flavidus may also have been influenced by the col-
lection of mostly small larvae (Rohlfs & Mack
1985). Gross & Pair (1991) state that 0. flavidus
parasitized 4th, 5th, and 6th instar fall army-
worm with equal success, but were minimally
successful in completing development on late 6th
instars. Although 0. flavidus does not kill the host
until the late prepupal or pupal stage, Rohlfs and
Mack (1983) found that parasitized larvae con-
sumed 17 to 22% less artificial diet than unpara-
sitized larvae.
Results of this survey suggest a need for more
taxonomic studies of parasitic hymenoptera in
Mexico, especially for Meteorus sp., Chelonus sp.,
and Chelonus sp. prob. cautus. All of the deter-
mined species, except Pristomerus spinator, have
ranges which extend into the U.S.A. However,
they may not be evenly distributed throughout
Mexico. This study was only a partial survey of
these areas of Mexico within a defined time
frame, during the rainy season when most corn is
grown. A thorough survey would require sam-
pling all developmental stages of fall armyworm
to evaluate the importance of parasitoids that de-


velop in the egg, pupal, and adult stages through-
out the growing season for corn and sorghum over
several years to determine if the differences seen
in this study were due to location, the develop-
mental stage of the host crop, or the developmen-
tal stage of the fall armyworm larvae. Additional
ecological studies are needed to determine where
and how the fall armyworm and its various natu-
ral enemies survive the dry season when few
crops are available.

ACKNOWLEDGMENTS
The authors express their gratitude to Robert W.
Carlson, Paul M. Marsh, and Michael E. Schauff (USDA
Systematid Entomology Laboratory, Beltsville, MD) for
their assistance in the identification of specimens.
This project was supported in part by Specific Coop-
erative Agreement #58-6602-7-F101 between the United
States Department of Agriculture, Agricultural Re-
search Service and the Universidad de Colima, Mexico.

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Florida Entomologist 84(1)







Armyworm Symposium 2000: Buntin et al.


EVALUATION OF YIELDGARD TRANSGENIC RESISTANCE
FOR CONTROL OF FALL ARMYWORM AND CORN EARWORM
(LEPIDOPTERA: NOCTUIDAE) ON CORN

G. DAVID BUNTIN', R. DEWEY LEE2, DAVID M. WILSON3 AND ROBERT M. MCPHERSON4
1Department of Entomology, University of Georgia, Georgia Experiment Station, Griffin, GA 30223

2Department of Crop and Soil Sciences, Rural Development Center, University of Georgia, Tifton, GA 31793

3Department of Plant Pathology, Coastal Plain Experiment Station, University of Georgia, Tifton, GA 31793

4Department of Entomology, Coastal Plain Experiment Station, University of Georgia, Tifton, GA 31793

ABSTRACT

Fall armyworm, Spodoptera frugiperda (J. E. Smith), and corn earworm, Helicoverpa zea
Boddie, perennially cause leaf and ear damage to corn in the southeastern USA. Develop-
ment of transgenic hybrids expressing insecticidal endotoxin from Bacillus thuringiensis
(Bt) offers a new approach to managing these insects in field corn. Transgenic Bt hybrids
with either the Bt11 or MON810 event, collectively known as YieldGard Technology, were
evaluated for control fall armyworm and corn earworm in southern Georgia during 1998,
which coincided with a severe outbreak of fall armyworm. YieldGard Bt resistance consis-
tently reduced whorl infestation and damage to low levels and also reduced ear infestations
and larval numbers per ear. However, larval establishment did occur on many ears of resis-
tant plants, but once established in ears, larvae of both species developed more slowly and
caused much less kernel damage on resistant than susceptible plants. We found no relation-
ship between YieldGard Bt resistance and corn grain aflatoxin concentrations. Yield re-
sponses were variable with the prevention of yield loss being proportional to the severity of
insect damage. These results indicate that YieldGard resistance is effective in preventing
significant losses to field corn by fall armyworm and corn earworm. Further, evaluation un-
der a variety of growing conditions and insect infestation levels is needed to clearly assess
the value of YieldGard technology to corn growers in the Southeast.

Key Words: Plant resistance, Spodoptera frugiperda, Helicoverpa zea, Transgenic crops, Bt
resistance

RESUME

Spodoptera frugiperda (J.E. Smith), y Helicoverpa zea Boddie, perennemente causan dano
de hoja y mazorca al maiz en el sureste de los Estados Unidos de America. El desarrollo de
hibridos transg6nicos que expresan la endotoxina insecticide de Bacillus thuringiensis (Bt)
ofrece una nueva practice para controlar estos insects en campos de maiz. Hibridos trans-
genicos Bt, ya sea con event Btll o MON810, colectivamente conocidos como tecnologia
YieldGard, fueron evaluados para control de S. frugiperda y H. zea en el sur de Georgia du-
rante el 1998, lo cual coincidi6 con una epidemia several de S. frugiperda. Resistencia Yield-
Gard Bt consistentemente redujo infestaci6n de cogollo y dahos a niveles bajos y tambien
redujo infestaci6n de mazorca y el numero de larvas por mazorca. Sin embargo, estableci-
miento larval si ocurri6 en numerosas mazorcas de plants resistentes, pero una vez esta-
blecidas el la mazorca, larvas de ambas species se desarrollaron mas lentamente y
causaron much menos daho de grano en plants resistentes que en las susceptibles. No en-
contramos ninguna relaci6n entire resistencia YieldGard Bt y concentraciones de aflatoxina
en granos de maiz. Producci6n de cosechas fueron variables con la prevenci6n de perdida de
producci6n siendo proporcional a la severidad del daho por insecto. Estos resultados indican
que resistencia YieldGard es efectiva en prevenir perdidas significativas de maiz de campo
por S. frugiperda y H. zea.


Fall armyworm, Spodoptera frugiperda (J. E. tantly they infest ears causing direct loss of grain.
Smith), and corn earworm, Helicoverpa zea Bod- Insecticidal control is difficult and generally not
die, are the most important insect pests of corn in cost effective in field corn. Typically, early plant-
the southeastern U.S. Both insects infest whorl ing times are recommended in the Southeast
stage plants causing leaf injury, but more impor- partly to avoid damaging levels of both insects







Florida Entomologist 84(1)


which often occur later in the season. Germplasm
with moderate levels of leaf feeding resistance to
fall armyworm has been released (Williams et al.
1997, 1998). High levels of resistance to fall army-
worm and corn earworm in silks of the tropical
corn 'Zapalote Chico' also have been identified
(Wiseman & Windstrom 1986). However, these
natural sources of plant resistance have not been
effectively deployed.
Transgenic corn hybrids expressing the insec-
ticidal protein CrylAb from Bacillus thuringien-
sis (Bt) var. kurstaki were originally developed to
control European corn borer, Ostrinia nubilalis
(Hiibner) and offer the potential for reducing
losses by fall armyworm and corn earworm. Sev-
eral events of transgenic Bt corn have been devel-
oped with different modes of toxin expression
(Ostlie et al. 1997). The most promising events
are Btll (Novartis Seeds) and MON810 (Mon-
santo Co.) where endotoxin is expressed in vege-
tative and reproductive structures throughout
the season (Armstrong et al. 1995; Williams et al.
1997). Hybrids containing either of these events
are collectively referred to as having 'YieldGard
Technology' (Ostlie et al. 1997). Laboratory feed-
ing trials and small controlled field trials have
shown that hybrids containing the Btll event re-
duce fall armyworm and corn earworm growth
and survival (Williams et al. 1997, 1998). Yield-
Gard resistance also is very effective against
Southwestern corn borer (Archer et al. 2000; Wil-
liams et al. 1998), but this insect either does not
occur or is not economically important in the
coastal plain region of the southeastern U.S.
Because of concerns about the potential for corn
earworm to develop virulence to Bt technology in
transgenic cotton, YieldGard transgenic corn was
not commercially deployed in the Southeast until
1998. In a series of studies at five locations in Ala-
bama in 1998 with corn planted at the recom-
mended time and 1 and 2 months later, DeLamar
et al. (1998a-e) demonstrated that YieldGard resis-
tance (events MON810 and Bt11) prevented whorl
damage, kernel damage, and yield loss by lepi-
dopterans, primarily fall armyworm and corn ear-
worm, in later plantings at all locations. YieldGard
resistance generally did not improve the perfor-
mance of corn planted at recommended times, be-
cause these plantings generally escaped severe
lepidopteran damage. YieldGard resistance has
not been evaluated in the field under natural infes-
tations of fall armyworm or corn earworm in Geor-
gia. Furthermore, lepidopteran infestations of ears
have been linked with increased levels of fungal in-
fection and contamination of grain by mycotoxins
such as aflatoxin produced by Aspergillus flavus
(e.g., Windstrom 1979; McMillian 1983; McMillian
et al. 1985; Smith & Riley 1992). Effective reduc-
tion in lepidopteran ear infestations with trans-
genic Bt resistance may also help reduce aflatoxin
contamination of grain (Williams et al. 1998).


Our objective was to evaluate the effect of both
YieldGard Technology events on fall armyworm
and corn earworm infestations and damage and
on grain aflatoxin contamination of field corn.
Trails were conducted in southern Georgia during
the summer of 1998 and coincided with a severe
outbreak of fall armyworm.

MATERIALS AND METHODS

Trials were conducted on a Greenville sandy
loam soil at the Univ. of Georgia Southwest
Branch Experiment Station near Plains, and on a
Tifton sandy loam soil at the Attapulgus Research
Center near Attapulgus and the Coastal Plain Ex-
periment Station near Tifton. The study area at
each location was fertilized, chisel plowed or sub-
soiled twice, and disk harrowed. Before disking
440 kg/ha of 3-18-9 (N-P-K) granular fertilizer
was applied and an additional 112 kg of nitrogen
was applied as ammonium nitrate about 20 d af-
ter planting. Seed at all locations was planted
with an air-planter at the rate of 66,700 plants per
ha. Pendimethalin (Prowl) at 0.71 L/ha and atra-
zine (Aatrex) at 0.57 L/ha were applied to control
weeds. No other pesticides were applied. Natural
rainfall was supplemented by irrigating weekly
with 6 cm/ha of water as needed at all locations.
The experimental design within each planting
date and location was a split plot design with
whole plots being brand (manufacturer) and split
plots being hybrid pairs within manufacturer. At
Attapulgus a single planting occurred on 23 April
1998. Planting dates were conducted as separate
side-by-side trails with two dates at Tifton (13
and 23 April 1998) and three dates at Plains (14
April, 12 May and 3 June 1998). Hybrid pairs
were a Bt hybrid and a non-Bt isoline or near iso-
line hybrid. Susceptible and Bt-resistant hybrid
pairs at Plains were Pioneer Brand 3223 and
31B13 (Bt), Golden Harvest (Monsanto) 2530 and
2530Bt, Dekalb DK 591 and DK 591BtY, and No-
vartis N79-P4 and N79L3 (Bt). Pairs at Tifton
were Pioneer Brand 3223 and 31B13 (Bt), Pioneer
Brand 3394 and 33V08 (Bt), and Novartis N79-P4
and N79L3 (Bt). Pairs at Attapulgus were Pioneer
Brand 3223 and 31B13 (Bt), Dekalb DK 591 and
DK 591BtY, and Novartis N79-P4 and N79L3
(Bt). Whole plots were arranged in a randomized
complete block design with four replications at
Attapulgus and the first and second planting
dates at Plains and 3 replications at both plant-
ings at Tifton and the third date at Plains. Plots
measured 15.2 m by 6 rows (76-cm rows) at
Plains, 21.3 m by 4 rows (91-cm rows) at Attapul-
gus and 9.1 m by 4 rows (91-cm rows) at Tifton.
Whorl defoliation was assessed by rating 30
plants (all plants at Tifton) in the two center rows
per plot about 6 wk after planting at the 8-10 leaf
stage for each planting date. Plants were rated for
damage using a 0-9 scale (Davis et al. 1992)


March 2001







Armyworm Symposium 2000: Buntin et al.


where 0 is no damage and 9 is whorl and furl al-
most completely defoliated. The damage scale is
not linear with ratings of >4 indicating substan-
tially more damage than ratings of_<3. Twenty to
30 larvae were collected for species identification
from infested whorls in rows at the edge of plots.
Ear damage of 12 ears per plot was assessed by
counting the number of live larvae and larval
feeding cavities and measuring the total length of
all feeding cavities for each ear (Windstrom 1967).
Ear infestations were sampled twice at Attapul-
gus with live larvae in the first sample being iden-
tified to species and categorized as small, medium
or large and final ear damage being assessed at
the second sample.
The two center rows of each plot were harvested
with a Hege two-row corn combine on August 12,
September 1, and September 12 for the three re-
spective planting dates at Plains and 20 August at
Tifton. At Attapulgus, plots (all 4 rows) were har-
vested on 10 August using a John Deere 4420 com-
bine with a 4-row corn head modified for small plot
harvesting. Grain yields were adjusted to 15.5%
moisture content. A 2-kg subsample of grain was
collected from each plot in trials at Plains and At-
tapulgus for determination of grain aflatoxin lev-
els. Kernels were ground to pass a 20 mesh screen,
well mixed, and 100 g subsample were extracted.
Aflatoxin contamination was determined using the
Vicam immunoaffinity column method (Truckness
et al. 1991) and is reported as total aflatoxin (B1 +
B2 + G, + G2) in parts per billion of seed.
Results were analyzed within each planting date
and location with an analysis of variance for a split
plot design. Before analysis, percentage data were
transformed by square-root arcsine, and numeric
data were transformed by loglo(x + 1). Significance
of main effects for brand (manufacturer) and hy-
brid resistance (i.e., Bt verses non-Bt) were deter-
mined using F test at P = 0.05. Brand x hybrid-
resistance interactions were not significant (P =
0.05) for any parameter. Therefore, only hybrid
resistance main effects (i.e., average across all
brands) are presented for the combined analyses.


RESULTS

Species Composition

Fall armyworm populations reached damaging
outbreak levels earlier than normal in 1998 re-
sulting in the worst damage to corn in Georgia in
the last decade. Whorl infestations in all trials
consisted almost entirely of fall armyworm. Ear
infestations at Attapulgus (N = 430 larvae) were
89% fall armyworm and 11% corn earworm. At
Tifton, ear infestations were 90% fall armyworm
and 10% corn earworm in both plantings (N =
178). At Plains, fall armyworms accounted for
11%, 48% and 73% of total live larvae observed in


ears of all hybrids in the first (N = 75), second (N
= 131), and third planting (N = 33) dates, respec-
tively, with the balance being corn earworm.

Whorl Infestations and Damage

Hybrid brand did not significantly (P = 0.05)
affect the percentage of infested whorls or mean
damage rating per plant and per infested plant in
any trial. Whorl infestations and damage in-
creased substantially from the first to third plant-
ings at Plains, but were similar between plantings
at Tifton (Table 1). YieldGard Bt resistance
greatly reduced whorl infestations, whorl damage
ratings per plant and whorl damage rating per in-
fested plant at Attapulgus and in all plantings at
Plains (Table 1). Whorl infestations and whorl
damage ratings also were smaller in resistant
than susceptible hybrids in both plantings at Tif-
ton. However whorl infestations were much lower
at Tifton than at the other locations, and differ-
ences were not significant in either planting.

Ear Infestations and Damage

Hybrid brand main effects were not significant
(P = 0.05) in any trial for the percentage of in-
fested ears or mean damage rating per ear and
per infested ear. Ear infestations in susceptible
hybrids were uniformly high in all trials, but ear
damage became progressively more severe in
later plantings at Tifton and Plains (Table 2). The
percentage of infested ears was reduced in resis-
tant hybrid in all plantings at Tifton and Plains,
although 30% to 70% of ears of resistant hybrids
were infested. However, at Attapulgus all ears of
susceptible hybrids and almost every ear of resis-
tant hybrids were infested. YieldGard resistance
significantly reduced the number of larval cavi-
ties which is a direct measure of the number of
larvae per ear in all trials (Table 2). Furthermore,
resistance also greatly reduced the amount of
damage per ear and per infested ear in all trials,
with the exception of the damage per infested ear
in the first planting at Tifton.
Many larvae were present in ears during the
first ear sample at Attapulgus. The size distribu-
tion of larvae reveals that the majority of fall
armyworms and corn earworms were medium
sized (i.e., instars 3 and 4) in ears of Bt resistant
plants, but most larvae were large sized (i.e., in-
stars 5 and 6) in ears of susceptible plants (Fig. 1).

Grain Yield and Aflatoxin Levels
Grain yield and aflatoxin level were not signif-
icantly different between brands in any trial, ex-
cept at Attapulgus where both Pioneer brand
hybrids yielded more than the other hybrids. This
difference in yield presumably is due to differ-
ences in agronomic characteristics and not to dif-
ferences in insect resistance.







Florida Entomologist 84(1)


March 2001


TABLE 1. MEAN (SE) WHORL INFESTATION AND WHORL DAMAGE RATING CAUSED BY FALL ARMYWORM IN SUSCEPTI-
BLE AND 'YIELDGARD' RESISTANT CORN IN GEORGIA, 1998.

Planting Bt Infested Damage rating' Damage rating'
Location date resistance whorls (%) per plant per infested plant

Attapulgus 23 March 83.3 + 2.2 4.0 + 0.3 4.9 + 0.2
+ 13.8 + 1.8 0.5 + 0.1 3.2 + 0.4
F 675.83*** 303.82*** 16.81**
Tifton 13 April 12.3 + 2.2 0.23 + 0.06 1.77 + 0.13
+ 6.9 + 1.5 0.10 + 0.02 1.42 + 0.11
F 2.03 ns 2.14 ns 2.09 ns

23 April 8.8 + 0.4 0.14 + 0.03 1.75 + 0.49
+ 4.4 + 1.9 0.05 + 0.02 1.16 + 0.06
F 2.33 ns 2.42 ns 1.19 ns

Plains 14 April 23.3 + 3.2 0.5 + 0.1 2.1 + 0.2
+ 9.2+ 1.8 0.1+ 0.1 1.0+ 0.2
F 19.64** 24.56** 19.75**

12 May 49.4 + 5.4 2.5 + 0.3 5.1 + 0.2
+ 14.1 + 3.6 0.5 + 0.2 3.8 + 0.3
F 42.79** 37.22*** 18.35**

3 June 96.1+ 1.4 5.4 + 0.2 5.6 + 0.1
+ 35.0+ 2.6 1.1+ 0.1 3.4+ 0.1
F 283.41*** 1068.67*** 45.08***

ns, **, *** indicate not significant and significant at P = 0.01 andFP = 0.001, respectively.
'Rating scale of Davis et al. (1992) where 0 is no damage and 9 is whorl and furl destroyed.




TABLE 2. MEAN (SE) EAR INFESTATION, CAVITY NUMBER AND LENGTH CAUSED BY FALL ARMYWORM AND CORN EAR-
WORM IN SUSCEPTIBLE AND 'YIELDGARD' RESISTANT CORN IN GEORGIA, 1998.

Planting Bt Infested Larval cavities Damage rating' Damage rating'
Location date resistance ears (%) per ear per ear per infested ear

Attapulgus 23 March 100.0 + 0 2.4 + 0.1 8.9 + 0.6 8.9 + 0.6
+ 96.5 + 1.6 1.1 + 0.1 2.7 + 0.2 2.8 + 0.2
F 4.48 ns 90.89*** 135.79*** 131.21***

Tifton 13 April 81.5 + 4.0 0.9 + 0.1 2.3 + 0.2 2.7 + 0.2
+ 28.7 + 7.9 0.3 + 0.1 0.7 + 0.2 2.0 + 0.3
F 45.73*** 67.73*** 37.82*** 2.42 ns

23 April 93.5 + 4.0 1.1 + 0.1 4.0 + 0.2 4.3 + 0.1
+ 53.7 + 4.9 0.6 + 0.1 1.3 + 0.4 2.3 + 0.6
F 30.61** 34.65*** 25.40** 15.25**

Plains 14 April 91.0 + 2.4 1.21 + 0.18 4.3 + 1.2 4.7 + 0.1
+ 36.8 + 7.2 0.38 + 0.25 0.9 + 0.2 2.2 + 0.2
F 63.77** 124.22*** 392.57*** 97.81***

12 May 95.3 + 2.0 1.43 + 0.32 5.7 + 0.6 5.9 + 0.6
+ 68.2 + 4.7 0.73 + 0.22 1.9 + 0.3 2.7 + 0.2
F 54.89*** 37.17*** 37.56*** 23.69**

3 June 94.4 + 2.0 1.77 + 0.34 7.5 + 0.7 7.9 + 0.6
+ 40.7 + 6.0 0.41 + 0.18 0.9 + 0.1 2.1 + 0.2
F 288.74*** 142.16*** 104.88*** 104.48***

ns, **, *** indicate not significant and significant at P = 0.01 andFP = 0.001, respectively.
'Rating scale of Windstrom (1967) where 0 is no damage.







Armyworm Symposium 2000: Buntin et al.


Small Medium Large Small Medium Large
Fall armyworm Corn earworm
Fig. 1. Size distribution fall armyworm and corn ear-
worm larvae in ears of susceptible and Bt resistant corn
hybrids at Attapulgus, GA, 1998.


YieldGard resistance at Attapulgus prevented
significant yield (F = 113.29; df = 1, 9;P = 0.0001)
losses in all brands of hybrids (Fig. 2). Resistance
in this trial prevented an average yield loss of
28% which equaled 2141 kg/ha (=34.1 bu/acre).
Grain yields at Tifton were not significantly dif-
ferent between Bt resistant types in either plant-
ing (Date 1:F = 0.14; df= 1, 9;P = 0.72; Date 2: F
= 0.08; df = 1, 9; P = 0.79).
Grain yields at Plains were low for all planting
dates with yields being greatest on the second
planting date (Fig. 2). Average grain yields were
not significantly (F = 0.01; df= 1, 12;P = 0.98) dif-
ferent between susceptible and resistant hybrids
on the first planting date. YieldGard resistance
prevented significant grain yield losses of 21.8%
during the second planting date (F = 15.27; df = 1,


12; P = 0.0021) and 74.5% during the third plant-
ing date (F = 128.41; df= 1, 9;P = 0.0001).
Grain aflatoxin concentrations were extremely
high at Attapulgus and in the first planting at
Plains. Aflatoxin progressively declined to low
levels with later plantings at Plains (Fig. 3).
Grain aflatoxin concentrations were not signifi-
cantly different between susceptible and Bt-resis-
tant hybrids in any trial (Attapulgus: F = 2.58, df
= 1, 9, P = 0.14; Plains PD1:F = 0.50, df= 1, 12,P
= 0.50; Plains PD2: F = 0.20, P = 0.66; Plains PD3:
F = 0.81, df = 1, 9, P = 0.40).

DISCUSSION
YieldGard Bt resistance consistently pre-
vented whorl infestation and damage by fall ar-
myworm. Even when larvae established on
resistant plants, whorl damage of infested plants
was substantially reduced. YieldGard resistance
also reduced lepidopteran infestations and the
number of larvae in ears, but larval establish-
ment did occur on many ears of resistant plants.
Indeed, at Attapulgus, where large numbers of
fall armyworm predominated, Bt resistance did
not reduce the percentage of infested ears. How-
ever, once established in ears, larvae of both spe-
cies developed more slowly and caused much less
kernel damage on ears of resistant than suscepti-
ble plants. The lack of significant brand by resis-
tance interactions for any variable measured also
verifies that hybrids with the Btll and MON810
events were similar in efficacy controlling in
whorl and ear infestations for both species.
Despite reports showing an association be-
tween lepidopteran damage and aflatoxin contam-
ination of corn grain (e.g., Windstrom 1979;
McMillian 1983; McMillian et al. 1985; Smith &
Riley 1992), we found that YieldGard Bt resistance


23 March 13 April 23 April 14April 12 May 3 June
Atlapulgus Tifton Tifton Plains Plains Plains
Fig. 2. Grain yield (+SE) of susceptible and Bt resis-
tant corn hybrids planted at three location in southern
Georgia in 1998.


tl
23 March 14 April
Attapulgus Plains


* Non Bt
QB1


12 May 3 June
Plains Plains


Fig. 3. Grain aflatoxin concentration (SE) of suscep-
tible and Bt resistant corn hybrids at Attapulgus and
three planting times at Plains, GA in 1998.











did not affect aflatoxin concentrations in grain. Al-
though YieldGard Bt resistance prevented most
kernel damage, larvae frequently established on
resistance ears. Newer events with high levels of
toxin expression that virtually prevent larval es-
tablishment may be needed to effectively test the
hypothesis that lepidopterans infestations en-
hance aflatoxin contamination of corn grain.
Growing conditions in 1998 were hot and very
dry causing most dryland corn production to be
destroyed. Yield of irrigated corn also was reduced
because of high temperatures during most of the
season and especially during pollination and silk-
ing. Hybrid yields of plantings at Plains were low
and do not permit useful economic comparisons of
the value of YieldGard technology. However, grain
yields at Attapulgus were typical of this location
in 1998. Assuming no large differences in grain
quality and at a grain price of $76.52 per Mg (=
$2.00 per bu), the average yield loss of 2141 kg/ha
(= 34.1 bu/acre) produced a $168.45 per ha (=
$68.20 per acre) gross return from YieldGard
technology in this one trial. However, economic
benefit must be more extensively evaluated under
a variety of growing conditions and insect infesta-
tions levels to clearly assess the value of Yield-
Gard technology to corn growers in the Southeast.


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Florida Entomologist 84(1)







Armyworm Symposium 2000: Carpenter et al.


FECUNDITY AND LONGEVITY OF DIAPETIMORPHA INTROITA (CRESSON)
(HYMENOPTERA: ICHNEUMONIDAE) REARED ON ARTIFICIAL DIETS:
EFFECTS OF A LIPID EXTRACT FROM HOST PUPAE AND CULTURE
MEDIA CONDITIONED WITH AN INSECT CELL LINE

J. E. CARPENTER, S. M. FERKOVICH2 AND P. D. GREANY3
1Crop Protection and Management Research Unit
Agricultural Research Service, U. S. Department of Agriculture, Tifton, GA 31793-0748

2Center for Medical, Agricultural, and Veterinary Entomology, USDA, ARS
1700 SW 23rd Drive, PO Box 14565, Gainesville, FL 32604

3University of Florida, Gainesville, FL

ABSTRACT

Diapetimorpha introita (Cresson) (Hymenoptera: Ichneumonidae) is a native ectoparasitoid
of Spodoptera spp. pupae. This parasitoid has been reared in the laboratory on an artificial
diet devoid of any insect host components. However, wasps reared on this artificial diet had
reduced fecundity. Efforts to increase fecundity included supplementing the diet with cell
culture media conditioned with a cell line from ovaries of the fall armyworm, S. frugiperda,
in one experiment and fortifying the diet with lipids extracted from pupae of S. frugiperda
in a second experiment. In the first experiment, differences in mean oviposition and mean
longevity among females reared on the artificial control diet (artificial diet), cell line-supple-
mented diet (S19Cell), and natural host (Host) were not significant. However, during the first
10 days of oviposition, Sf9Cell-reared females oviposited at a rate similar to the Host-reared
parasitoids and at a rate faster than artificial-diet reared females. In the second experiment,
females reared on the diet with added host lipid (host lipid) laid significantly more eggs than
females on the artificial diet, however, longevity was not significantly affected by diet treat-
ment. We conclude that total egg production by D. introita was improved on artificial diet
supplemented with lipids from the natural host but was not increased by the addition of ma-
terials produced by an ovarial cell line derived from S. frugiperda. Future research efforts
should focus on increasing fecundity of wasps reared on the artificial diet by identifying the
lipid(s) or lipid-soluble material in the host pupal extract that is responsible for enhancing
egg production in D. introita females.

Key Words: Diapetimorpha introita, Spodoptera, parasitoid, artificial diet, fecundity, host
lipids, insect cell line

RESUME

Diapetimorpha introita (Cresson) (Himen6ptera: Ichneumonidae) es un ectoparasito nativo
en pupas de species de Spodoptera. Este parasito ha sido criado en el laboratorio en una
dieta artificial desprovista de components de insecto hospedero. Sin embargo, avispas cria-
das en esta dieta artificial tuvieron fecundidad reducida. Esfuerzos para incrementar la fe-
cundidad incluyeron: suplir la dieta con medio de cultivo de celulas acondicionadas con una
linea de celulas de ovarios de S. frugiperda en un experiment, y fortificando la dieta con li-
pidos extraidos de pupas de S. frugiperda en un secundo experiment. En el primer experi-
mento, diferencias en oviposici6n promedio y longevidad promedio entire hembras criadas
bajo la dieta artificial de control (artificial diet), la dieta complementada con linea de celulas
(Sf9Cell), y hospedero natural (Host) no fueron significantes. Sin embargo, durante los pri-
meros 10 dias de oviposici6n, hembras criadas con Sf9Cell ovipositaron a una velocidad si-
milar a los parasitos criados con Host y a una velocidad mas rdpida que hembras criadas con
artificial diet. En el segundo experiment, hembras criadas con la dieta complementada con
lipidos de hospedero (host lipid) pusieron significativamente mas huevos que hembras con
artificial diet, sin embargo, la longevidad no fue afectada significativamente por el trata-
miento de dieta. Concluimos que producci6n total de huevos por D. introita fue mejorada por
la dieta artificial complementada con lipidos del hospedero natural pero no fue incremen-
tada por la adici6n de materials producidos por la linea de celulas de ovario derivada de S.
frugiperda. Futuros esfuerzos de studio deberan enfocarse en incrementar la fecundidad de
avispas criadas con la dieta artificial al identificar el lipido (s) o material soluble en lipidos
en el extract pupal de hospedero que es responsible por aumentar la producci6n de huevos
en hembras de D. introita.







Florida Entomologist 84(1)


Diapetimorpha introita (Cresson) (Hymen-
optera: Ichneumonidae) is a native ectoparasitoid
of Spodoptera spp. (Pair & Gross 1984) that has
been reared in the laboratory on an artificial diet
devoid of any insect components (Carpenter &
Greany 1998; Greany & Carpenter 1996). Female
parasitoids that are reared on this artificial diet
are able to search for and parasitize natural hosts
in the field (Carpenter and Greany 1998). How-
ever, survival rate, fecundity, and weight are less
for diet-reared D. introita than for host-reared D.
introita. Also, developmental time is significantly
longer for wasps reared on the artificial diet than
for wasps reared on host pupae (Carpenter & Gre-
any 1998). Efforts to increase wasp weight and re-
duce developmental time have included the
addition of commercial nutrients, the use of cul-
ture media conditioned by insect cell lines, and
supplementing the diet with lipid extracts from
host pupae (Ferkovich et al. 1999; Ferkovich et.
al., in press). One of the cell lines, Sf, derived from
ovaries of S. frugiperda resulted in some improve-
ment in wasp weight (Ferkovich et al. 1999),
whereas, the use of a lipid extract from S. fru-
giperda not only enhanced the average weight of
the males and females but also reduced their
developmental time. Other parameters such as
cocoon production or adult emergence were unal-
tered. Molting hormone titers of diet-reared and
host-reared D. introita were examined and it was
concluded that insufficient ecdysteroid in the
hemolymph during metamorphosis may contrib-
ute to the lowered emergence in wasps reared on
the artificial diet (Gelman et al. 1999).
In view of some of the positive effects on
growth and development of D. introita with di-
etary supplements of extracted host lipids and
cell line-conditioned media (Ferkovich et al. 1999,
Ferkovich et al., in press), we decided to examine
their effects on fecundity and longevity of D. in-
troita females.

MATERIALS AND METHODS
Insect Rearing

Insects used in this study were obtained from
laboratory colonies at the Crop Protection and
Management Research Unit, Tifton, GA. D. in-
troita were reared according to the methods de-
scribed by Pair (1995), unless noted otherwise. S.
frugiperda larvae were reared in plastic cups (30
ml) containing meridic diet (Burton 1969) at a
photoperiod of 14:10 (L:D) h and temperature of
28 + 1 and 25 + 1C, respectively.

Diet Preparation and Encapsulation of Diet

The original artificial diet (control diet) con-
tained ground beef liver, chicken egg yolk, and the
amino acid L-glutamine (Sigma, St. Louis, MO)


and was prepared according to Carpenter and
Greany (1998) under aseptic conditions in a clean
room as described by Ferkovich et al. (1999). All
the ingredients were added to 25 ml of serum-free
SF-900 II cell culture medium. The diet was en-
capsulated in Parafilm using a diet encapsula-
tion apparatus (Greany & Carpenter 1996). Diet
was dispensed at 0.5 ml of diet/dome with 24
domes/sheet. Each diet sheet was covered with a
modified (bottomless) Falcon tissue culture
plate (Sigma, St. Louis, MO) so that each dome
(one larva/dome) was situated within a well. The
entire culture plate was covered with a Plexiglas
plate to prevent escape of the larvae. Diet was
changed during larval development four days af-
ter the neonates were initially placed on the diet.

Preparation of Cell line-supplemented Diet

The Sf9 cell line was an embryonic line origi-
nally derived from ovaries of the fall armyworm,
S. frugiperda, and purchased from ATCC, Rock-
ville, MD. The cells were cultured in Grace's me-
dium with 10% fetal bovine serum (FBS), 1%
bovine serum albumin (BSA) and 0.33% lactalbu-
min enzymatic hydrolysate (Sigma, St. Louis,
MO). For larger-scale culture of the cell lines, cells
were grown in 250 ml magnetic spinner flasks
(Bellco Glass, Vineland, NJ) at 29C and were
grown to densities of 1.3 x 105 to 2 x 105 cells/ml 10
days post inoculation. For the experiments, 25 ml
of cell suspension were centrifuged at 250x g for
2 min at room temperature. The resultant cell-
conditioned supernatant then was substituted for
the SF-900-II medium in preparing the artificial
treatment diets. Two cell line control diets were
also tested to measure the effects of Grace's cul-
ture medium and the additives FBS, 1% BSA and
0.33% lactalbumin enzymatic hydrolysate, addi-
tives that were required for optimal cell growth.

Preparation of Diet With Extracted Host Pupal Lipids

Lipids were extracted using a modified method
of Folch et al. (1957) as described by Ferkovich et
al. (in press). Briefly, twenty-four 4 day-old pupae
of Spodoptera frugiperda pupae were homoge-
nized in 12.5 ml of Ringers solution (Ephrussi &
Beadle 1936); the homogenate was filtered through
glass wool to remove cuticular debris and the fil-
trate saved. The filtrate was then extracted with
a chloroform:methanol (2:1) mixture and the chlo-
roform phase was dried down.
Twenty-five ml of diet were added to the dried
chloroform extract and the flask was rotated for 5
min to dissolve the residue. The chloroform ex-
tract of freshly homogenized pupae of S. fru-
giperda was added to the artificial diet so that
each diet dome contained one pupal equivalent of
lipid per D. introita larva.


March 2001







Armyworm Symposium 2000: Carpenter et al.


Treatment Diets

The treatment diets used in this study were as
follows: 1) Host, S. frugiperda pupae; 2) artificial
diet, original control diet; 3) host lipid, original
diet containing chloroform-extracted lipids from
freshly homogenized S. frugiperda pupae (pre-
pared according to the methods described by Fer-
kovich et al., in press); 4) Sf9ControlA, artificial
diet prepared with Grace's cell culture medium,
5) Sf9Control,, artificial diet prepared with
Grace's cell culture medium with % bovine serum
albumin, 10% fetal bovine serum and lactalbumin
enzymatic hydrolysate; and 6) Sf9Cell, diet pre-
pared with S9 cell-conditioned Grace's medium
with 1% bovine serum albumin, 10% fetal bovine
serum and lactalbumin enzymatic hydrolysate.

Bioassay

First instar larvae that hatched within a 12
hour period were placed on encapsulated diet
domes (one larva/dome) in individual cells of a 24
well plate. Each treatment was replicated four
times. The larvae were allowed to feed and de-


80


70


40


20


Sf9Cell


Artificial


velop to adults (described below) at 29.1 + PC
and 70% RH. Diet was replaced four days after
the neonates were initially placed on the diet
domes. The third instar larvae were transferred
to the new diet domes using a camel hair brush. A
24 well plate containing 24 larvae on a diet con-
stituted one replication. As the adults emerged,
they were held individually in plastic portion
cups (102 cc) for 24 hrs before they were weighed.

Oviposition and Longevity Studies

Ten male and ten female wasps from each
treatment were randomly selected, weighed 24 h
post emergence, and paired in small (480 ml)
plastic containers fitted with screened lids. Each
container was maintained with a source of honey
and water. A plastic cup (30 ml) containing 15 ml
of soil in which a S. frugiperda larva had pupated
was provided for each female wasp as an oviposi-
tion site. Cups were replaced daily and the num-
ber of eggs laid by each female wasp was
recorded. Longevity of male and female wasps
was recorded.


Host


I Std. Dev.
+1 Std. Err.
0 Mean


Fig. 1. Comparison of mean oviposition by female Diapetimorpha introita reared on: Host (Spodoptera fru-
giperda pupae), artificial diet, original control diet; S/9Control,, artificial diet prepared with Grace's cell culture
medium; S/9ControlB, artificial diet prepared with Grace's cell culture medium with 1% bovine serum albumin, 10%
fetal bovine serum and lactalbumin enzymatic hydrolysate; and S/9Cell, diet prepared with S9 cell-conditioned
Grace's medium with 1% bovine serum albumin, 10% fetal bovine serum and lactalbumin enzymatic hydrolysate.


a

ab




I
1_ -3 b




a


Sf9Control,
Sf9Control A







Florida Entomologist 84(1)


" 0 10 20 30 40

DAY

Fig. 2. Rate of oviposition by female Diapetimorpha introita reared on: Host (Spodoptera frugiperda pupae), ar-
tificial diet, original control diet; S/9ControlA, artificial diet prepared with Grace's cell culture medium; S/9ControlB,
artificial diet prepared with Grace's cell culture medium with 1% bovine serum albumin, 10% fetal bovine serum
and lactalbumin enzymatic hydrolysate; and S/9Cell, diet prepared with S9 cell-conditioned Grace's medium with
1% bovine serum albumin, 10% fetal bovine serum and lactalbumin enzymatic hydrolysate.


Statistical Analysis

The treatment means for fecundity and lon-
gevity were compared using the t-test (Steel &
Torrie 1980). Regression analysis (StatSoft 1995)
was used to examine the relationship between
mean fecundity and female longevity.

RESULTS

Diet Supplementation with Sf9 Cell Line-Conditioned
Medium

Mean oviposition of females reared on the arti-
ficial diet, Sf9Cell and Host treatments was not
significantly different, and only females reared on
the Sf9Cell and Host diet treatments oviposited
significantly (P < 0.05) more eggs than females
reared on the two control diets, Sf9ControlA and
Sf9Controlt (Fig. 1). However, during the first ten
days females reared on the Sf9Cell diet and the
Host oviposited at a faster rate than females
reared on Sf9ControlA diet and artificial diet (Fig.
2). When data from all diet treatments were com-
bined, there was a significant (P < 0.001, R2 =
0.999) relationship between mean oviposition and


female longevity (Fig. 3). However, there were no
significant differences in mean longevity of female
wasps among the five treatments (artificial diet,
24.4d; Sf9Cell, 23.5d; Host, 18.8d; Sf9ControlA,
20.1d; and Sf9Controls, 20.1d).

Diet Supplementation with Host Pupal Lipid Extract

Although females developing on the host lipid
diet and the artificial diet demonstrated similar
patterns in oviposition (Fig. 4), the mean ($ S.D.)
number of eggs laid by females reared on the host
lipid diet (46.67 $ 8.7) was significantly (t = 4.39,
df = 8, P = 0.002) more eggs than the number of
eggs laid by females reared on the artificial diet
(34.67 $ 10.5). The difference in longevity of fe-
males reared on the two diets was not significant
(artificial diet, 16.86 $ 7.7 days and Host Lipid,
22.50 $ 7.7 days).

DISCUSSION

The fecundity of females was increased with
the addition of lipids from host pupae to the arti-
ficial diet. The concentration of lipid added to the
diet was one pupal equivalent per parasitoid; this


March 2001







Armyworm Symposium 2000: Carpenter et al.


-1U '
0 10 20 30 40 50

FEMALE LONGEVITY (Days)

Fig. 3. Relationship between oviposition and longevity for female Diapetimorpha introita reared on host pupae
(Spodoptera frugiperda) and artificial diets (y = 21.4 + 4.74x 0.015x2 0.001x3, R2 = 0.999, P < 0.0001).


concentration was selected because a single para-
sitoid develops on one host pupa in the wild (Pair
1995). It is possible, however, that fecundity could
be improved further with the addition of a higher
concentration of host lipid extract. At present, the
identity of the bio-active compound active is not
known. It could either be a lipid(s) or a lipid-solu-
ble compoundss. If the material is a lipid(s), it
would be difficult to speculate as on the identity of
the material since the dietary lipid requirements
in parasitoids vary with the species. Many species
of parasitoids copy the lipid composition of their
host (Thompson & Barlow 1972). Others such as
Exeristes roborator Fab. (Thompson 1977) are able
to regulate their fatty acid concentrations in the
absence of the dietary lipids. Still others such as
Agria house (SlI.. -; ll) (House 1954) and Itoplec-
tis conquisitro (Say) (Yazgan 1972) can be reared
on a diet without fatty acids but supplementation
of fatty acids to the diet improves adult emergence
and fecundity. Other parasitoids such as Pimpla
turionellae (L) require fatty acids in their diet to
produce normal looking adults (Yazgan 1981).
Reinecke (1985) stated that all insects have
certain lipid dietary requirements, especially the
immature stages, however very few of these lipids
are essential and only the sterols are universally
required. Thus, it is interesting that the lipids


present in the egg yolk component of the artificial
diet did not adequately support fecundity ofD. in-
troita. Egg yolk-based diets have been used to
rear a number of parasitoids and predators
(Grenier et al. 1994; Nelson 1999). The egg yolk in
this artificial diet either lacked the required
lipid(s) or contained the needed lipid(s) but not in
levels adequate for higher fecundity. Supplement-
ing the diet with host lipids apparently provided a
better nutritional balance to the diet, allowing
the D. introita females to oviposite at a signifi-
cantly higher rate than females reared on the
artificial control diet. Bracken (1969) found that
sustained egg production for adults of the para-
sitoid, Exeristes comstockii was dependent on a
balance of nutrients in the artificial diet.
Wheeler (1996) indicated that oogenesis is typi-
cally a nutrient-limited process and is initiated only
if sufficient nourishment is taken for egg produc-
tion. Nourishment for D. introita egg production is
apparently acquired during the larval stage be-
cause the ovaries of the females are well developed
at adult emergence (pers. obs.), and females are
able to produce eggs throughout their adult lives by
feeding only on honey and water (Pair 1995).
Cell line-conditioned media have been used to
improve the growth of two endoparasitoids, Lysi-
phlebus fabarum (Marshall) (Rotundo et al. 1988)


o
0 0
0


o


0 N
0







Florida Entomologist 84(1)


50



Ca 40
E
()
LL
-30

0-
Co
D 20
LU

CU
a) 10


0 *I I I I I I I I I I I I I I I I I I I!
1 3 5 7 9 11 13 15 17 19 21 23 25 27

Days

Fig. 4. Rate of oviposition by female Diapetimorpha introita reared on: artificial diet, original control diet; and
host lipid, original diet containing chloroform-extracted lipids from freshly homogenized Spodoptera frugiperda pu-
pae (prepared according to the methods described by Ferkovich et al., in press).


and Microplitis croceipes (Ferkovich et al. 1994),
and an egg ectoparasitoid, Edouum puttleri, (Hu
et al. 1999). However, fecundity could not be as-
sessed in these studies because the insects either
did not develop to the adult stage or only low
numbers of adults emerged on the cell line-sup-
plemented diets. In this study, we were able to ex-
amine the effects of the cell conditioned medium
on fecundity because successive generations can
been produced on the artificial diet (Carpenter &
Greany 1998). The positive effect the Sf9Cell diet
had on the increased rate of oviposition with no
accompanying effect on the mean oviposition rate
was interesting. It appears that the cell line pro-
duced an unknown material that induced the fe-
males to deposit their eggs in a pattern that
paralleled Host-reared females and at a rate
faster than artificial diet- reared females (Fig. 2).
In view of the positive effects of the pupal lipid
extract on fecundity of D. introita, we suggest
that future research should focus on identifying
the fecundity-enhancing materials) from host
pupae so that it can more easily be tested at var-
ious concentrations in the diet. Moreover, once
the identity of the material is known, it may be
possible to obtain it from a commercial source.


ACKNOWLEDGMENTS
We thank Robert Caldwell and Susan Drawdy (In-
sect Biology and Population Management Research
Laboratory, USDA-ARS), and Delaine Miller (Center for
Medical, Agricultural, and Veterinary Entomology,
USDA, ARS) for their technical assistance in this study.

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Armyworm Symposium 2000: Carpenter et al.


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Florida Entomologist 84(1)


SEASONAL ABUNDANCE OF A PUPAL PARASITOID,
DIAPETIMORPHA INTROITA (HYMENOPTERA: ICHNEUMONIDAE)

D. K. JEWETT1 AND J. E. CARPENTER2
'USDA, ARS, Northern Plains Agricultural Research Laboratory
1500 North Central Avenue, Sidney, MT 59270

2USDA, ARS, Insect Biology and Population Management Research Laboratory
2747 Davis Road, Tifton, GA 31793

ABSTRACT
Seasonal abundance of a pupal parasitoid Diapetimorpha introita (Cresson) (Hymenoptera:
Ichneumonidae) and the beet armyworm Spodoptera exigua (Huibner) (Lepidoptera: Noctu-
idae) was monitored with pheromone-traps. D. introita males were caught in wing traps
baited with live females, and beet armyworm males were caught in bucket traps baited with
synthetic pheromone. The greatest number of D. introita adult males was caught during
early autumn, approximately one month after the greatest number of beet armyworm males
was caught, and represents the most convenient time during which to conduct trapping ex-
periments.

Key Words: sex-attractant, biological control, population dynamics, beet armyworm, fall
armyworm, Spodoptera, pheromone-trapping

RESUME
La abundancia estacional del parasito pupal Diapetimorpha introita (Cresson) (Himen6p-
tera: Ichneumonidae) y de Spodoptera exigua (Htibner) (Lepid6ptera: Noctuidae) fue obser-
vada con trampas de feromona. Machos de D. introita fueron capturados en trampas de ala
con senuelo de hembras vivas, y machos S. exigua fueron capturados en trampas de cubo con
senuelo de feromona sintetica. La mayor capture de machos adults D. introita fue alcan-
zada durante el comienzo del otono, aproximadamente un mes despues de que el mayor nu-
mero de S. exigua fue capturado, y represent el tiempo mas convenient para conducir
experiments de trampas.


When the Boll Weevil Eradication Program
was initiated in autumn of 1987 over large por-
tions of the southeastern United States, the beet
armyworm Spodoptera exigua (Hiibner) (Lepi-
doptera: Noctuidae) emerged as the most impor-
tant threat to cotton production (Haney et al.
1996). Other hosts of economic importance with
which the beet armyworm is associated include
tomatoes, corn, alfalfa, onions, asparagus, pota-
toes, and citrus as well as numerous non-eco-
nomic species (Hendricks et al. 1995). Prior to
1991, Georgia experienced outbreaks during
1977, 1980, 1981, 1988, and 1990 (Douce &
McPherson 1991). Difficult to manage, outbreaks
have been correlated with less than normal pre-
cipitation and disruptive insecticide use (Chan-
dler & Ruberson 1996). Its threat to cotton
production has declined in recent years, presum-
ably the result of declining insecticide applica-
tions directed at the boll weevil and increased
planting of BT-cotton against the beet armyworm
(John Ruberson, Department of Entomology, Uni-
versity of Georgia, pers. comm.).
Historically, the fall armyworm Spodoptera
frugiperda (J. E. Smith) is an important pest of


corn, sorghum, and coastal Bermuda grass (Met-
calf et al. 1951). It was not recognized as an im-
portant threat to cotton production. Recently,
however, the importance of fall armyworm to cot-
ton production has increased (Riley et al. 1997)
because BT-cotton is not as effective against it as
beet armyworm (Adamczyk et al. 1998).
Diapetimorpha introita (Cresson) (Hymenop-
tera: Ichneumonidae) is a pupal parasitoid native
to southern Georgia, and it may be valuable to the
biological control of Spodoptera spp. if mass prop-
agated and released against incipient populations
(Pair & Gross 1989). It has been reared from fall
armyworm pupae collected in the field (Pair &
Gross 1989). AlthoughD. introita has been reared
from laboratory strains of the beet armyworm
(Carpenter & Greany 1998), a comprehensive sur-
vey of pupae in the field has yet to be completed.
Previous attempts to describe population dy-
namics of D. introita have relied upon measuring
frequency of parasitism among fall armyworm
pupae in the field (Pair & Gross 1989). As investi-
gation of D. introita and its importance to the
management of Spodoptera spp. proceeds, more
convenient methods of monitoring populations in


March 2001







Armyworm Symposium 2000: Jewett & Carpenter


the field are needed (Jewett & Carpenter 1998).
One possible approach to monitoring D. introita
concerns pheromone-trapping males. That D. in-
troita males use a sex-attractant to find females is
supported by data from laboratory and field bio-
assays (Jewett & Carpenter 1998). Significantly
more males were caught in traps baited with live
females than in traps baited either with nothing
or with live males. Experiments with a related
pupal parasitoid, Ichneumon promissorius (Hymen-
optera: Ichneumonidae) (Erichson), have yielded
further insights concerning extraction of a sex-
attractant from D. introita females (Jewett & Car-
penter 1999).
A lure formulated with the sex-attractant of
D. introita for conveniently monitoring its popu-
lations in the field is anticipated. Field bioassays
had been completed previously during spring and
early summer, and number of males caught in
traps was generally low (Jewett & Carpenter
1998). A greater population reservoir from which
to trap D. introita males would accommodate
more replications and greater resolution. The
present study was undertaken to describe local
seasonal abundance of D. introita males, and to
identify the most convenient time of year during
which they may be trapped.
For comparison, local seasonal abundance of
the beet armyworm also was considered. Al-
though a comprehensive survey of beet army-
worm pupae in the field has not been completed,
more D. introita were reared from beet army-
worm pupae than from fall armyworm pupae
(Carpenter & Greany 1998). Relative abundance
of the fall armyworm was not considered because
it is not resident to southern Georgia, but instead
migrates annually from Florida (Pair et al. 1986;
Wilson 1934). This disposition may be responsi-
ble, in part, for inconsistent trapping results and
their lacking reliability as indicators of relative
abundance (John Ruberson, Department of Ento-
mology, University of Georgia, pers. comm.). Un-
able to rely upon results of trapping fall armyworm
males, beet armyworm was substituted because it
is a potential host that responds well to lures.

MATERIALS AND METHODS

Twenty different sites at Gibbs and Bellflower
Farms in Tift Co. were monitored for D. introita
adult males during two years. Traps were estab-
lished as described by Jewett and Carpenter
(1998). Briefly, wing traps were supported 0.5 m
above ground and were baited with two live fe-
males (either mated or unmated) (Fig. 1). Number
of males caught was recorded once a week, and
trap bottoms were replaced. Lures also were re-
placed once a week or when a female had expired.
Sex-attractant of the beet armyworm is (z)-9-
tetradecen-1-ol (2.5%), (z)-9, 12-tetradecadien-l-
ol acetate (87.2%), and (z)-11-hexadecen-l-ol ace-


tate (10.3%). It has been used previously to trap
beet armyworm adult males (Hendricks et al.
1995; Mitchell & Tumlinson 1994), and is as reli-
able an indicator of seasonal occurrence of beet
armyworm adults in the field as live virgin fe-
males (Mitchell & Tumlinson 1994). Beet army-
worm adult males were monitored at Gibbs and
Rigdon Farms in Tift Co., Georgia with traps es-
tablished as described by Ruberson and Herzog
(1997, 1998). Briefly, bucket traps were sus-
pended 1.5 m from the ground and were baited
with lures of synthetic pheromone (Great Lakes
IPM Inc., Vestaburg, MI). Number of males
caught in traps was recorded once a week and
lures were replaced biweekly.
Adult males of both insects were monitored be-
tween June 1997 and December 1998. Occasion-
ally, data were not recorded from beet armyworm
traps during 1998 or fromD. introita traps during
1997. Data were not recorded from beet army-
worm traps during the last two weeks of Decem-
ber in 1997 and the first two weeks of January in
1998. Data were not collected from D. introita
traps during January 1997.

RESULTS AND DISCUSSION

Although pheromone-traps have been used to
detect insects at remarkably low population den-
sities, the number caught often does not reflect
actual density (Carde & Elkinton 1984). However,
data from trapping programs often are valuable
for relative estimates (Evans 1984). Results of
trapping D. introita adult males in the present
study are generally consistent with those of the
previous study by Pair and Gross (1989), al-
though some differences do exist. In the present
study, greatest number of D. introita males was
caught during September and early October of
both years (Fig. 2). Pair and Gross (1989) also re-
ported that emergence ofD. introita from fall ar-
myworm pupae was greatest during September
and October. During the present study, twenty
one males were caught over 2 days in one trap at
Gibbs Farm in October, and two traps caught 23
males each during one week in September at Bell-
flower Farm (Fig. 2).
D. introita first appeared during May in the
study by Pair and Gross (1989), but in the present
study, males first appeared during the end of
March (Fig. 2). D. introita overwinter in their
hosts, and this difference in date of appearance
may reflect sensitivity of pheromone-traps to low
numbers that have emerged after overwintering.
Although Pair and Gross (1989) did not detect
D. introita adults between mid-July and end of
August, small numbers were detected during that
time in the present study (Fig. 2).
Greatest number of beet armyworm adult
males was caught in traps during August and
September. Total number caught exceeded 500 on







Florida Entomologist 84(1)


Fig. 1. In the field, wing trap baited with Diapetimorpha introita (Cresson) (Hymenoptera: Ichneumonidae)
females.


March 2001







Armyworm Symposium 2000: Jewett & Carpenter


Fig. 2. Average number of Diapetimorpha introita (Cresson) (Hymenoptera:Ichneumonidae) males caught in
wing traps baited with live females (solid line) and average number of beet armyworm Spodoptera exigua (Htibner)
(Lepidoptera: Noctuidae) males (intermittent line) caught in bucket traps baited with synthetic pheromone. Breaks
in either line represent weeks during which data were not collected.


only 4 dates in 1997, but never exceeded 1,000 as
it had in previous years (Ruberson & Herzog
1998). Total number caught in 1998 was compara-
ble to 1997 (Ruberson & Herzog 1997, 1998).
DeBach and Smith (1941) demonstrated that
oscillations are inherent to host-parasitoid sys-
tems. They predicted that if a parasitoid is host-
specific and more successful at finding abundant
hosts, then reduction in host numbers would re-
sult in decreased number of parasitoids, permit-
ting host numbers to rise (DeBach & Smith 1941).
Relative abundance of the beet armyworm andD.
introita males reflects oscillations predicted by
DeBach and Smith (1941) (Fig. 2). Greatest num-
ber ofD. introita males trapped for both years fol-
lowed the greatest number of beet armyworm
males trapped by approximately one month,
which is consistent with combined development
times of beet armyworm and D. introita (Wilson
1934; Pair 1995).
Pair and Gross (1989) concluded that abun-
dance of D. introita reflects availability of its host.
Although a direct host-parasitoid relationship be-
tween the beet armyworm andD. introita has not
been formally demonstrated in the field, it is sup-
ported by their population curves in the present
study and the successful rearing ofD. introita on
laboratory strains of the beet armyworm (Carpen-
ter & Greany 1998). Furthermore, the fall army-


worm is migratory from Florida (Pair et al. 1986;
Wilson 1934) and the beet armyworm could sat-
isfy any requirement D. introita has for an alter-
nate host in southern Georgia.
As investigation of their importance to biologi-
cal control of Spodoptera spp. proceeds, more con-
venient methods of monitoring D. introita in the
field are needed. The development of lures for
monitoring the relative abundance of males is an-
ticipated, but a need for populations large enough
to accommodate the convenient testing of differ-
ent formulations has been expressed. Results of
the present study suggest that the best time dur-
ing which to test different formulations of lures is
during early autumn, approximately one month
following greatest relative abundance of beet army-
worm adult males.


ACKNOWLEDGMENTS

We thank John Ruberson (Entomology Department,
University of Georgia, Tifton, GA) for providing beet
armyworm trap data. Also, we thank R. Caldwell and
S. Drawdy (Insect Biology and Population Management
Research Laboratory, USDA, ARS, Tifton, GA) for
their assistance. We are especially grateful for the
leadership of C. Rogers, former Laboratory Director
of the Insect Biology and Population Management
Research Laboratory.











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B. R. LEONARD, AND J. B. GRAVES. 1998. Susceptibil-
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JEWETT, D. K., AND J. E. CARPENTER. 1999. Chemically-
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Florida Entomologist 84(1)







Obrycki et al.: Geographic Populations of H. convergens


COMPARATIVE STUDIES OF THREE POPULATIONS OF THE LADY BEETLE
PREDATOR HIPPODAMIA CONVERGENS (COLEOPTERA: COCCINELLIDAE)

JOHN J. OBRYCKI1, ELLIOT S. KRAFSUR', CARLOS E. BOGRAN2, LUIs E. GOMEZ'AND RONALD E. CAVE4
1Department of Entomology, Iowa State University, Ames, IA 50011-3140

'Texas A & M University, Department of Entomology, College Station, TX 77843

34a Calle A, 10-66 Zona 3, Colonia Bella Vista, Quetzaltenango, Guatemala

4Departmento de Proteccion Vegetal, Escuela Agricola Panamericana, El Zamaorano, Honduras

ABSTRACT

Allozyme electrophoresis showed much genetic variation in Hippodamia convergens, sug-
gesting the possibility of geographic genetic differentiation. Twenty-two of 31 putative alloz-
yme loci resolved on acrylamide gels from H. convergens populations were polymorphic
(71%). Heterozygosity (diversity) averaged over all loci was 21.3 + 4.2%. However, thirteen
polymorphic loci examined in F1 Honduran x Iowa hybrids indicated that all alleles were
shared in the two populations. In addition, no significant geographic variation was observed
in developmental and reproductive responses of H. convergens from Iowa, California, and
Honduras to aphid prey densities. All inter-population and backcrosses produced fertile
eggs. Adult body size of H. convergens from Iowa and Honduras was similar. This study
indicates that augmentatively released California H. convergens could successfully mate
with local H. convergens populations in Iowa and Honduras.

Key Words: convergent ladybeetle, allozymes, gene diversity, augmentation, biological control

RESUME

Electroforesis de alozima demostr6 gran variaci6n genetica en Hippodamia convergens, su-
giriendo la posibilidad de diferenciaci6n genetica por geograffa. Veintid6s de 31 lugares de
alozimas putativas resueltas en geles de acrilamida de poblaciones de H. convergens fueron
polymorficos (71%). Heterozigosidad (diversidad) promedio sobre todos los lugares fue 21.3
+ 4.2%. Sin embargo, trece lugares polimorficos examinados en hibridos F1 Hondureno x
Iowa indicaron que todos los aleles fueron compartidos en ambas poblaciones. Adicional-
mente, no se observe variaci6n geografica significativa en respuestas reproductivas y de de-
sarrollo de H. convergens de Iowa, California, y Honduras a densidades de presa de afido. La
inter populaci6n y cruces de hibridos backcrosss" produjeron huevos f6rtiles. El tamano del
cuerpo adulto de H. convergens de Iowa y Honduras fue similar. Este studio indica que H.
convergens liberado aumentativamente pudiera aparear satisfactoriamente con poblaciones
locales de H. convergens en Iowa y Honduras.


Yearly mass collections and augmentative re-
leases of overwintering adult Hippodamia con-
vergens from California are made for aphid
suppression, even though evidence for effective-
ness is limited (Hagen 1962; Majerus 1994;
Hodek & Honek 1996; Obrycki & Kring 1998).
Dreistadt & Flint (1996) reported a temporary 3-
day decline in aphid densities following release of
H. convergens adults. Release of H. convergens
from California may have negative effects on local
populations ofH. convergens because of the distri-
bution of pathogens and parasitoids found in
adults (Lipa & Steinhaus 1959; Sluss 1968;
O'Neil et al. 1998). An additional concern that has
been raised for Danaus plexippus L., a species
that is also distributed widely by humans
(Brower et al. 1995), relates to the idea that


unique local populations with favorable co-
adapted genotypes may be compromised by re-
leases of foreign genotypes. Characterization of
H. convergens intra-specific variation is needed to
assess the potential effects of releases of Califor-
nia beetles on local H. convergens populations.
One trait that has been examined inH. conver-
gens populations from Arizona, Cuzco (Peru),
New York, and Oregon, is the thermal require-
ment for development (Butler & Dickerson 1972;
Escalante 1972; Obrycki & Tauber 1982; Miller
1992). Consistency in developmental thresholds
of H. convergens across geographically separated
populations in North America has been reported
by Miller (1992). However, earlier studies on H.
convergens reported differences in thermal re-
sponses between populations from Arizona and







Florida Entomologist 84(1)


New York (Butler & Dickerson 1972; Obrycki &
Tauber 1982). A second set of traits that may be
used to characterize intra-specific variation are
those related to predator responses to prey spe-
cies, e.g., prey suitability (Tauber et al. 1995).
The objectives of this study were to 1) compare
allozyme variation and developmental responses
of H. convergens from two North American (Iowa
and California) and one Central American (Hon-
duras) population to aphid prey, and 2) test for re-
productive isolation among H. convergens
populations from Honduras, Iowa, and California.

MATERIALS AND METHODS
Developmental Characteristics

In 1994, Hippodamia convergens adults were
collected at the Escuela Agricola Panamericana,
Zamorano, Honduras, and in Story and Marion
Counties, Iowa. Approximately 50 adult H. con-
vergens were sent from Honduras to the USDA-
ARS, Beneficial Insects Introduction Research
Laboratory, Newark, DE, where they were reared
for one generation. First laboratory generation
adults were sent to Iowa State University. Six
lines, each descended from a different single pair
mating, were established from Honduras beetles
and 10 lines were established from Iowa beetles;
eggs were collected daily. Pairs were kept at 24C,
(L:D) 16:8 and fed pea aphids, Acyrthosiphon
pisum (Harris), and green peach aphids, Myzus
persicae (Sulzer) ad libitum. Forty larvae from
each pair were reared individually on 2-4 A.
pisum per day at 24C, (L:D)16:8. Observations
on larval survival and developmental stage were
made every 24 h.
In 1997, H. convergens were collected in Ames,
Iowa, and in the Departamento Francisco Mora-
zan, Honduras. Adults from California were pro-
vided by Gardens Alive, Lawrenceburg, IN. Five
pairs from each population, (California, Iowa, and
Honduras) were maintained at 24C, 16:8 L:D;
eggs were collected daily. To examine develop-
mental responses to prey density, 25 first instars
from each population were reared on three levels
ofA. pisum: two per day, three per day and >20
per day.

Inter-population Crosses and Reproductive Responses

In 1994, 30 pairs of second laboratory genera-
tion individuals were established using virgin fe-
males from Honduran and Iowan populations: 3
pairs were Honduras x Honduras crosses, 3 were
Iowa x Iowa crosses, 12 were Iowa female x Hon-
duras male, and 12 were Honduras female x Iowa
male. Pairs were fed daily ad libitum with A.
pisum and M. persicae. Eggs were collected every
day for seven days to determine fecundity (num-
ber of eggs laid) and fertility (proportion of fertile


eggs). Following eclosion of at least half of the
eggs in each egg mass, the egg masses and newly
closed larvae were frozen to avoid cannibalism.
The number of fertile eggs in each egg mass was
estimated by adding closed larvae and darkened
eggs. Eggs were considered infertile if they were
pale yellow and slightly shrunken.
Fifteen larvae from each of the thirty mating
pairs were reared individually at 24C,(L:D)16:8.
Twelve adults from each cross were used in a
backcross experiment. Twelve pairs were back-
crossed to Honduras, [(HxIA) x (HxH)], 12 were
backcrossed to Iowa [(HxIA) x (IAxIA)], and 12
were Honduras x Iowa reciprocal crosses [(HxIA)
x (HxIA)]. The pairs were fed daily withA. pisum
and M. persicae. Eggs were collected every day for
7 days to determine fecundity and fertility. Obser-
vations of larval development and survival were
made every 24 h on ten larvae from each pair.
In 1997, F1 adults reared from Iowa, Califor-
nia, and Honduras populations were crossed.
Thirty pairs were established: 7 pairs were Iowa
females x Honduras males, 7 were Iowa males x
Honduras females, 3 were Iowa females x Califor-
nia males, 6 were Iowa males x California fe-
males, 6 were California females x Honduras
males, and 1 pair was California male x Hondu-
ras female. The pairs were fed >20A. pisum per
day for 15 days. When egg masses were observed,
they were placed in glass vials and held to deter-
mine fertility. Larvae were removed from the vi-
als daily to prevent cannibalism.

Size of adult H. convergens from Honduras and Iowa

To compare morphometric characteristics of H.
convergens adults from Honduras and Iowa, inter-
crosses, and reciprocal backcrosses, pronotal and
elytral length and width were measured by using
NIH image software (Macintosh version 1.57). Be-
fore measurements were taken, each adult was
pinned through the right elytron at exactly the
same distance from the head of the pin. Each bee-
tle was photographed using a color video camera
(JVC-TK1070U) mounted on a stereo zoom micro-
scope. The filmed images were digitally captured,
amplified and measured in millimeters.

Genetic Diversity Estimates

To estimate gene diversity, beetles from Hon-
duras and Iowa were killed by freezing and stored
at -80C. Reciprocal crosses of Honduras and
Iowa beetles provided hybrid progeny; 46 of which
were frozen for genetic analysis. Procedures for
preparing ladybeetle homogenates for allozyme
electrophoresis, histochemical demonstration of
putative loci, and statistical methods were those
already published (Krafsur et al. 1996a, b).
Voucher specimens of H. convergens are depos-
ited in the Iowa State University Insect Collection.


March 2001







Obrycki et al.: Geographic Populations of H. convergens


Data Analysis

In 1994, data obtained from rearing and adult
body measurements were summarized by mating
pair and means were calculated. Five variables
were compared among the populations, crosses
and backcrosses, using analysis of variance
(PROC GLM, SAS Institute 1985): developmental
time, survivorship, fecundity, fertility and adult
body size. Means were separated by using a least
significance difference test (LSD). Percentage
survival and fertility were arcsine transformed
[arcsine ( two-way ANOVA was used to compare the effects
of aphid prey and population of H. convergens on
development and survival.
A preliminary analysis revealed that the adult
body measurements were correlated to each
other. Thus, adult size was compared among
groups using an average of the four standardized
body measurements. The standardization was
done by subtracting the measurement mean
among groups from each measurement, and then
dividing by the standard deviation among groups.

RESULTS

Developmental Responses

Individuals from Honduras required approxi-
mately 3-4 more days to complete preimaginal de-
velopment than individuals from Iowa, Honduras
x Iowa crosses, and the backcrosses to Honduras
and Iowa (Table 1). Similarly, in 1997, Honduran
beetles reared on 2A.pisum per day required 27.3
+ 3.2 days to complete development, approxi-
mately 2-5 days longer then the Iowa and Califor-
nia beetles (Table 2). Developmental time varied
with population (F = 98.63; df= 2,101; P = 0.001),
sex (F = 7.89; df = 1,101; P = 0.048), diet (F =
514.6; df = 2,101; P = 0.001) and the interaction


between population and diet (F = 14.3; df = 4,101;
P = 0.012).
Preimaginal survival of H. convergens from
Honduras and Iowa and the Honduras Iowa
crosses ranged from 78 to 89% (Table 3). In 1997,
survivorship of Iowa, California, and Honduras
beetles on three levels of aphid prey was similar;
no effect of population (F = 5.81; df = 2,4; P =
0.066) or diet (F = 1.88; df = 2,4; P = 0.265) was ob-
served (Table 2). For Iowa and Honduran H. con-
vergens, survivorship increased with higher
levels of A. pisum per day, but this was not ob-
served for the California beetles (Table 2).

Reproductive Responses

No differences were observed among groups in
fertility and fecundity, however, large variation
within groups was observed in both fecundity and
fertility (Table 4). Fertility ranged from 70-76%
and 79-94% for the Honduran and Iowan popula-
tions, respectively. Fertility ranged from 4-93% for
the Honduras x Iowa crosses, 66-96% for the back-
crosses to Honduras, and 34-97% for backcrosses
to Iowa. In 1997, all 30 crosses among California,
Iowa, and Honduras H. convergens produced sim-
ilar numbers of fertile eggs (Gomez 1998).

Size of Adult Hippodamia convergens

The average pronotal width and length of Hon-
duras and Iowa H. convergens was 2.68 and 1.27
mm, respectively (Table 5). The average elytral
width and length among these groups was 2.16
and 4.98 mm, respectively (Table 5). Significant
differences were observed among original popula-
tions, crosses and backcrosses in the standard-
ized female body size (F = 7.96; df = 4, 51; P =
0.001) but not in the standardized male body size
(F = 0.42; df = 4, 45; P = 0.79).


TABLE 1. DEVELOPMENTAL TIME (DAYS; X SE) OF HIPPODAMIA CONVERGENS FROM HONDURAS, HONDURAS x IOWA
CROSSES AND RECIPROCAL BACKCROSSES; REARED ON 2-3 APHIDS PER DAY, 24C, L:D 16:8.

Days SE"'b

N' Egg Instar I Instar II Instar III Instar IV Pupa Egg-Adult

Honduras 89(6) 3.9 + 0.2 3.7 + 0.5 2.6 + 0.3 2.9 + 0.5 6.9 + 0.5 a 7.0 + 0.8 a 26.9 + 1.4 a
Iowa 236(8) 3.5 + 0.2 3.2+ 0.1 2.1 +0.1 2.5+ 0.1 6.8 + 0.3 a 5.3 + 0.1b 23.1 + 0.6 b
Hon x IA 424(36) 3.6 +0.1 3.2+ 0.1 2.4 +0.1 2.6 +0.1 5.9+ 0.1b 5.6+ 0.1b 23.4 + 0.2 b
F1 x Hon 160(12) 3.5 + 0.2 3.6+ 0.3 2.6 +0.2 2.8 +0.1 6.2 0.2 ab 5.6 0.3 b 24.3 + 0.4 b
F1 x IA 87(9) 3.7 +0.1 3.4+ 0.3 2.3 0.2 2.9+ 0.2 6.1 0.3 b 5.4 0.1b 23.7 + 0.4 b

(F; df) (1.2; 4, 64) (1.4; 4, 64) (1.1; 4, 64) (1.5; 4, 64) (3.9; 4, 64) (3.8; 4, 64) (6.9; 4, 64)
(P) (0.304) (0.246) (0.344) (0.210) (0.007) (0.008) (0.001)

Values represent means of mating pairs.
Means followed by the same letter in a column are not statistically different (P > 0.05).
Number of individuals (number of pairs).







Florida Entomologist 84(1)


March 2001


TABLE 2. DEVELOPMENTAL TIME, SURVIVAL, AND ADULT CHARACTERISTICS OF THREE POPULATIONS OF HIPPODAMIA
CONVERGENS REARED ON THREE LEVELS OF ACYRTHOSIPHON PISUM; 24C; 16:8 L:D; 1997.

Dev. time Survival" Sex ratio Female Male
Population A. pisum/day Days; X + SD % F: M weight (mg) weight (mg)

Honduras 2 27.3 + 3.2 52 [13] 5:8 8.7 + 2.3 8.0 + 0.4
3 23.4 + 2.0 56 [14] 8:6 8.5 + 1.6 8.9 + 0.9
>20 16.8 + 1.0 84 [21] 15:6 24.8 + 3.6 19.3 + 2.6
Iowa 2 24.6 + 1.2 48 [12] 3:9 8.2 + 0.7 6.9 + 0.4
3 21.4 + 2.2 56 [14] 5:9 10.1 + 0.6 8.3 + 0.6
>20 16.9 + 0.6 72 [18] 11:7 21.7 + 2.5 17.9 + 1.5
California 2 21.7 + 1.1 28 [7] 3:4 8.4 + 1.5 8.3 + 0.8
3 19.5 + 1.1 44 [11] 6:5 10.7 + 1.3 9.1+ 1.1
>20 15.7 + 1.0 28 [7] 5:2 25.6 + 3.0 21.4 + 4.0

Numbers in square parentheses = number of H. convergens that completed development; 25 first instars started on each aphid diet.


In 1997, sex (F = 23; df = 1,101; P = 0.009), lev-
els of aphid prey provided to the larvae (F = 412.3;
df= 2,101; P = 0.001) and the interaction between
diet and sex (F = 7.83; df = 3,101; P = 0.001) af-
fected weight of adult H. convergens, but no dif-
ferences among populations were observed (F =
4.89; df = 2,101; P = 0.084) (Table 2). A positive
correlation was observed between levels of A.
pisum provided to larvae and adult weight of
Iowa (R2 = 0.91), California (R2 = 0.92) and Hon-
duras (R2 = 0.87) H. convergens.

Genetic Diversity

Of 31 putative allozyme loci resolved on acry-
lamide gels, 22 were polymorphic (71%). Het-
erozygosity (diversity) averaged over all loci was
21.3 4.2%; an average 2.9 0.3 alleles per locus
was observed (Table 6). The heterozygosity of only
polymorphic loci was 30 4.8% with 3.6 + 1.3 al-
leles. The distribution of single locus heterozygos-
ities (Fig. 1) shows high levels of diversity and is


consistent with the neutral theory of mutations
(Nei et al. 1976). Examination of F1 Honduran x
Iowa hybrids at 13 polymorphic loci showed no al-
leles not detected in North American beetles.

DISCUSSION

Response to aphid prey levels was similar
among populations, even thoughA. pisum has not
been reported from Honduras and therefore may
not be a common prey species there (Castro 1993).
Total developmental time was inversely corre-
lated with the number of aphid prey provided to
H. convergens larvae. A reduction of more than 4
days in the total developmental time was ob-
served when aphid prey was increased from 3 to >
20A.pisum per day. Similarly, a reduction in total
developmental time was observed for the hemi-
pteran predator Podisus maculiventris (Say)
when fed greater quantities of Mexican bean bee-
tle larvae, Epilachna varivestis Mulsant (Legaspi
and O'Neil 1994).


TABLE 3. PERCENTAGE SURVIVAL (X SE) FOR LIFE STAGES OF HIPPODAMIA CONVERGENS FROM HONDURAS, IOWA,
HONDURAS x IOWA CROSSES AND RECIPROCAL BACKCROSSES.

Survival (% + SE) *

Instar I Instar II Instar III Instar IV Pupa Preimaginal

Honduras 90.0 + 4.5 ab 97.0 + 1.6 96.2 + 3.3 97.2 + 2.3 95.0 + 5.0 78.1 + 8.1
Iowa 98.6 + 0.7 b 96.9 + 1.6 98.4 + 0.9 97.9 + 0.9 96.6 + 1.3 88.9 + 2.1
Hon x IA 95.1 +1.4 b 97.1 + 0.9 99.5 + 0.4 97.3 + 1.0 98.9 + 0.6 88.3 + 1.7
F1 x Hon 87.7 + 3.9 a 94.4 + 3.1 98.3 + 1.7 97.6 + 2.4 94.8 + 2.8 76.7 + 6.4
F1 x IA 92.2 + 2.8 ab 98.8 + 1.1 96.5 + 2.4 99.1 + 0.9 98.6 + 1.4 85.7 + 2.3

(F; df) (2.54; 4, 64) (0.47; 4, 64) (1.30; 4, 64) (0.36; 4, 64) (1.43; 4, 64) (1.32; 4, 64)
(P) (0.04) (0.75) (0.28) (0.83) (0.23) (0.27)

'Means followed by the same letter in a column are not statistically different (P > 0.05).







Obrycki et al.: Geographic Populations of H. convergens


TABLE 4. MEAN FECUNDITY AND PERCENTAGE FERTILITY OF HIPPODAMIA CONVERGENS EGGS FROM HONDURAS AND
IOWA, THEIR OFFSPRING (HONDURAS x IOWA) AND RECIPROCAL BACKCROSSES.

Fecundity Fertility (%)

Group N" (X + SE) min. max. (X + SE) min. max

Honduras 6 119.0 + 32.8 59 172 73.7 + 1.5 70.1 76.3
Iowa 8 120.7 + 56.0 24 218 84.7 + 4.7 79.2 94.0
Hon x IA 35 111.8 + 8.8 7 225 72.0 3.3 4.4 93.5
F1 x Hon 12 119.8 + 10.8 23 208 84.8 + 0.2 66.1 95.5
F1 x IA 12 104.8 + 10.0 31 188 76.0 + 3.6 34.0 97.2

(F; df; P) (0.11; 4, 55; 0.97) (1.58; 4, 55; 0.24)

aNumber of females.


Total developmental times of H. convergens
from Iowa, California, and Honduras fed > 20A.
pisum per day were approximately 3 days shorter
than H. convergens from Arizona, Oregon and
New York (20 days) reared at similar tempera-
tures (Miller 1992, Obrycki & Tauber 1982).
Hagen and Sluss (1966) showed that developmen-
tal time and life span of H. convergens from Cali-
fornia were influenced by prey species. Thus,
these observed differences might be due to the use
of different aphid species among studies. Butler
and Dickerson (1972) reared H. convergens on the
cotton aphid,Aphis gossypii Glover, andA. pisum,
whereas Miller (1992) used the Russian wheat
aphid, Diuraphis noxia (Mordvilko), and the oat-
bird cherry aphid, Rhopalosiphum padi (L). Dif-
ferences in developmental time between beetles
fed > 20 A. pisum per day in our study and those
reared by Obrycki & Tauber (1982) on A. pisum
may be due to geographical variation.
The size of H. convergens crosses and back-
crosses are within the ranges described by Gordon


(1985). Weight of adult H. convergens was highly
correlated to levels ofA. pisum provided to larvae.
When the prey provided was increased from 3 to
>20A. pisum per day, adult weights doubled.
Hippodamia convergens from Iowa, Honduras,
and California mated and exhibited similar fe-
cundity and fertility. The number of eggs pro-
duced per day by H. convergens inter-population
crosses (14 to 17 eggs per day) was slightly lower
than that observed by Hagen & Sluss (1966) for
California H. convergens (20 eggs per day). The fe-
cundity of H. convergens was higher in our study
than that observed by Wipperfiirth et al. (1987),
who fed beetles fewer aphids than they could con-
sume on a daily basis.
High levels of gene diversity have been de-
tected in several species of ladybirds (Krafsur &
Obrycki 1996; Krafsur et al. 1992, 1995, 1996a, b,
1997). Of the 11 coccinellid species examined,
only one, Coleomegilla maculata Degeer, shows
evidence of being a species complex (Munyaneza
& Obrycki 1998; Krafsur & Obrycki 2000). The


TABLE 5. SIZE OF PRONOTUM AND ELYTRA OF ADULT HIPPODAMIA CONVERGENS FROM HONDURAS AND IOWA, THEIR
OFFSPRING (HONDURAS x IOWA) AND RECIPROCAL BACKCROSSES.

Pronotum (mm; X + SD) Elytra (mm; X + SD)

Group Sex (N) Width Length Width Length

Honduras F (5) 2.88 + 0.12 1.42 + 0.06 2.46 + 0.18 5.30 + 0.18
M (4) 2.72 + 0.12 1.28 + 0.05 2.22 + 0.12 4.95 + 0.30
Iowa F (5) 2.65 + 0.20 1.34 + 0.11 2.26 + 0.17 5.01 + 0.27
M (5) 2.79 + 0.12 1.33 + 0.03 2.34 + 0.02 4.79 + 0.21
Hon x IA F (29) 2.68 + 0.22 1.26 + 0.10 2.13 + 0.15 5.01 + 0.45
M (30) 2.63 + 0.25 1.26 + 0.13 2.08 + 0.26 4.91 + 0.47
F1 x Hon F (11) 2.64 + 0.10 1.29 + 0.10 2.12 + 0.16 4.89 + 0.37
M (9) 2.90 + 0.12 1.31+ 0.11 2.38 + 0.16 5.27 + 0.27
F1 x IA F (9) 2.49 + 0.06 1.15 + 0.11 2.04 + 0.10 4.76 + 0.14
M (5) 2.74 + 0.09 1.21 + 0.08 2.23 + 0.10 5.06 + 0.11







Florida Entomologist 84(1)


TABLE 6. GENE DIVERSITY HE AT PUTATIVE ALLOZYME LOCI IN HIPPODAMIA CONVERGENS.

E.C. number Expected
Enzyme Locus system Buffer heterozygosity" he

Acid phosphatase Acph EC 3.1.3.2 NAM 0.539
Aconitase Aco EC 4.2.1.3 OD 0.502
Aldehyde oxidase Aox EC 2.6.1.1. NAM 0.623
Adenylate kinase Adk-1 EC 2.7.4.3. NAM 0.454
Adk-2 0
Arginine kinase Argk EC 2.7.3.3. NAM 0
Diaphorase Dia-1 EC 1.6.2.2. NAM 0
Dia-2 0
Esterase Est EC 3.1.1.- NAM
Fructose biphosphatase Fbp EC 3.1.3.11. NAM 0.237
Fumarate hydratase Fum EC 4.2.1.2. OD 0
Glucose-6-phosphate dehydrogenase G6pd EC 1.1.1.49 NAM 0.418
Glyceraldehyde-3-phosphate dehydrogenase G3pd EC 1.2.1.12 NAM 0.036
Glycerophosphate dehydrogenase Gpd EC 1.1.1.8. TBE 0
Hexokinase Hk EC 2.7.1.1. TBE 0.530
Hydroxy acid dehydrogenase Had-1 EC 1.1.1.30 NAM, OD 0.311
Had-2 0.234
Isocitrate dehydrogenase-1 Idh-1 EC 1.1.1.42 NAM 0.036
Isocitrate dehydrogenase-2 Idh-2 NAM 0.053
Malate dehydrogenase Mdh-1 EC 1.1.1.37 NAM, OD 0.102
Mdh-2 0
Malic enzyme Me-1 EC 1.1.1.40 OD 0
Mannose-6-P-dehydrogenase Mpi EC 5.3.1.8 NAM 0.114
Phosphoglucoisomerase Pgi EC 5.3.1.9 OD 0
Phosphoglucomutase Pgm EC 5.4.2.2 NAM, OD 0.201
6-Phosphogluconate dehydrogenase 6pgd EC 1.1.1.44 NAM 0.297
Sorbitol dehydrogenase Sdh EC 1.1.1.14 NAM 0.610
Superoxide dismutase Sod-1 EC 1.15.1.1 OD 0.018
Sod-2 0.036
Trehalase Tre EC 3.2.1.28 NAM 0.683
Triose-phosphate isomerase Tpi EC 5.3.1.1 NAM 0.086

Mean of polymorphic loci:He = 0.301; SD = 0.048
Mean of all loci (n = 31):He = 0.213; SD = 0.042
Expected proportions heterozygous when mating is random.


high levels of variation characteristic of ladybirds
is indicative of large population sizes and high
rates of gene flow, inferences supported by ecolog-
ical and genetic studies. High rates of gene flow in
H. convergens argue against the notion that dis-
ruption of co-adapted gene complexes (super-
genes) will cause local populations to decline
dramatically (see discussion in Dobzhansky &
Pavlovsky 1960). It remains to be determined if
supergenes exist in ladybirds, and if alternative
gene arrangements are lethal, or if a lower fre-
quency of supergene carriers somehow causes
populations to decline. Colonizing species such as
ladybirds must naturally accommodate alterna-
tive intervals of local inbreeding and invasion by
foreign genotypes throughout much of their evo-
lutionary history. Environmental influences,
rather than genetic, most likely explain the fail-
ure of deliberate ladybird introductions to become
established.


All inter-population H. convergens crosses in our
studies produced fertile eggs. Thus, no intrinsic
reproductive barriers exist among Iowa, Hondu-
ras, and California populations. If H. convergens
from California are augmentatively released in
Honduras or Iowa, individuals or their progeny
may interbreed. Our results indicate that ifH. con-
vergens from California do cross with local popu-
lations, no detrimental effects in F1 developmental
and reproductive parameters in response to one
species of aphid prey (A.pisum) may occur. Preda-
tion of other prey species of local importance may
need to be examined (Bogran & Obrycki 1998).
However, this does not mean that the F1 H. con-
vergens crosses would be well suited to local con-
ditions. For example, photoperiodic responses for
diapause induction may be different among Cali-
fornia and local populations ofH. convergens, and
this parameter could be altered in the F1 crosses
(see Tauber et al. 1997). The observed interbreed-


March 2001







Obrycki et al.: Geographic Populations of H. convergens


proportion of 31 loci
0.35 -


Hippodamia convergens


Avg. heterozygosity = 21.3%


25 50


% single locus heterozygosity

Fig. 1. Single locus heterozygosity (h) in Hippodamia convergens.


ing among California, Honduras, and Iowa bee-
tles, in addition to the presence of parasitoids and
pathogens in California adults, combined with
the lack of substantial evidence of effectiveness,
suggest that the practice of augmentative re-
leases of field collected H. convergens needs to be
carefully examined for non-target effects.

ACKNOWLEDGMENTS
We thank Dr. P. Hinz (Iowa State University) for as-
sistance in the statistical analyses, J. Van Dyk (Iowa
State University) for help with NIH software, and W.E.
Morjan (Iowa State University) for collecting H. conver-
gens in Honduras. We thank Niles Kinerk, Gardens
Alive, Indiana, for research funding and for providing
H. convergens from California. We also thank B. Lewis,
G. Glawe, R. Schneider, and B. Clark for technical help.
We thank Dr. D. Topel, Dean, College of Agriculture and
Dr. T. C. Baker, Chair, Department of Entomology for
providing graduate research assistantships to C.E.B.
and L.E.G. Journal Paper No. J-17979 of the Iowa Agri-
cultural and Home Economics Experiment Station,
Ames, Iowa, Project Nos. 3437 and 3447, and supported
by Hatch Act and State of Iowa funds.

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C=7


0.30 -


0.25 -


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0.15-


0.10-


0.05 -


0.00-


SD 4.28


75 100


--4.-












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Florida Entomologist 84(1)







Van Driesche et al.: Efficacy of Variable and Fixed Parasitoid Rates


EFFECT OF PARASITOID RELEASE PATTERN ON WHITEFLY
(HOMOPTERA: ALEYRODIDAE) CONTROL IN COMMERCIAL POINSETTIA

R. G. VAN DRIESCHE', M. S. HODDLE 2, S. ROY', S. LYON' AND J. P. SANDERSON3
1Department of Entomology, University of Massachusetts, Amherst, MA 01003

2Current address: Department of Entomology, University of California, Riverside, CA 92521

'Department of Entomology, Cornell University, Ithaca, NY 14853

ABSTRACT

Under commercial poinsettia production conditions we compared two patterns of parasitoid
release for the aphelinid whitefly parasitoid Eretmocerus eremicus Rose and Zolnerowich.
We compared the currently used pattern of a fixed weekly release number (3 females per
plant per week) to an experimental pattern in which more parasitoids were released early
in the crop (wks 1-8), followed by a lower number (wks 9-17), with the seasonal release av-
erage still being 3 female parasitoids per plant per week. We further compared the outcome
of these two treatments (fixed and variable) to a low release rate (1 parasitoid per pl per wk)
of Encarsia formosa Gahan, an aphelinid parasitoid widely used for whitefly control in
greenhouse crops. In control cages without parasitoid releases, whitefly nymphal densities
reached 15-32 live nymphs per leaf, which was 7 to 16-fold greater than the acceptable level
at crop harvest. In cages in which parasitoid releases were made, whitefly nymphal densities
were suppressed 99.8%, 96.8% and 50.9% by fixed-rate E. eremicus, variable-rate E. eremi-
cus, and low-rate E. formosa treatments, respectively. In greenhouse populations, the final
densities of live whitefly nymphs per leaf were significantly higher in the E. formosa treatment
than the two E. eremicus treatments. Releases of low numbers of E. formosa provided commer-
cially acceptable control in only one of two greenhouses. There was no difference between the
fixed and variable release rate treatments of E. eremicus, indicating that whitefly suppres-
sion was not increased by concentrating the release of this parasitoid early in the crop.

Key Words: Eretmocerus eremicus, Encarsia formosa, Bemisia argentifolii, poinsettia, bio-
logical control, variable release rate, augmentative release, evaluation, cost, greenhouses

RESUME

Dos patrons de liberaci6n de parasito para Eretmocerus eremicus Rose y Zolnerowhich fue-
ron comparados bajo condiciones de producci6n commercial de poinsettia (Flor de Pascua).
Comparamos el patron actualmente usado de numero de liberaci6n semanal fija (3 hembras
por plant por semana) a un patron experimental en el cual mas parasitos fueron liberados
temprano en el cultivo (semanas 1-8), seguido por un numero menor (semanas 9-17), con la
liberaci6n estacional promedio aun siendo 3 parasitas hembras por plant por semana. Adi-
cionalmente comparamos el resultado de estos dos tratamientos (fijo y variable) a una baja
incidencia de liberaci6n (1 parasito por plant por semana) de Encarsia formosa Gahan, un
parasito usado extensamente para control de la mosca blanca en cultivos de invernadero. En
jaulas de control sin liberaci6n de parasito, densidades de ninfas mosca blanca alcanzaron
15-32 ninfas vivas por hoja, que fue entire 7 y 16 veces mayor que el nivel acceptable al mo-
mento de cosecha del cultivo. Enjaulas en las cuales liberaci6n de parasito ocurri6, las den-
sidades de ninfas mosca blanca fueron suprimidas 99.8%, 96.8, y 50.9% por E. eremicus en
tratamientos fijo, variable, y tratamientos de baja incidencia de E. formosa, respectiva-
mente. En poblaciones de invernadero, las densidades finales de ninfas vivas de mosca
blanca por hoja fueron significativamente mayores en el tratamiento de E. formosa que en
los dos tratamientos de E. eremicus. Liberaciones de bajas cantidades de E. formosa prove-
yeron control acceptable en solo uno de dos invernaderos. No hubo diferencia entire los trata-
mientos fijo y variable de E. eremicus, indicando que supresi6n de mosca blanca no
incremento como causa de concentrar la liberaci6n de este parasito temprano en el cultivo.


Silverleaf whitefly (Bemisia argentifolii Bel- The principal parasitoid species used for its control
lows and Perring) (Homoptera: Aleyrodidae) is an have been Encarsia formosa Gahan and Eretmo-
important foliar pest of poinsettia (Euphorbia cerus eremicus Rose and Zolnerowich (Hymenop-
pulcherrima Willd. ex Koltz.) (Byrne et al. 1990; tera: Aphelinidae) (Drost et al. 1996, Hoddle &
Bellows et al. 1994; Hoddle & Van Driesche 1996). Van Driesche 1996; Rose & Zolnerowich 1997).







Florida Entomologist 84(1)


Trials to measure the efficacy of releases of com-
mercial E. formosa (Ef), the Beltsville strain of E.
formosa (EfBelt), or E. eremicus (Ee) on poinsettia
have examined constant weekly releases of either
one or three females per plant per week (Hoddle &
Van Driesche 1996; Hoddle et al. 1996; Hoddle et
al. 1997abc; Hoddle & Van Driesche 1999ab). In
small greenhouses holding 90 plants, whitefly
mortality (1- survivorship from egg to adult) was
99% (Ee and BfBelt, both high rate), 96% (EfBelt,
low rate), 95% (Ef, low rate), 92% (Ef high rate)
and 88% (Ee low rate) (Hoddle et al. 1997abc).
While these mortality rates may seem uni-
formly high, the differences among them have
practical importance because whiteflies in poin-
settia have four generations in the crop cycle,
each with high rates of population increase. With
no mortality from pesticides or parasitoids, silver-
leaf whitefly egg-to-adult survival is about 75%
(Hoddle et al. 1997abc). Combined with the per
female fertility rates that B. argentifolii can
achieve on poinsettia, this level of survival results
in rates of increase of up to 25-fold per generation.
With this rate of increase and an initial density
on cuttings in the range of 0.1 nymphs per leaf (a
typical value), an uncontrolled population has the
potential to exceed 12,000 per leaf by the end of
the crop (but actually would be constrained below
that level by competition, other sources of mortal-
ity, and space on the leaf). By comparison, if par-
asitoid-caused mortality decreased egg-to-adult
survival to 1% (99% mortality), whitefly density
would decrease over the course of the crop to less
than 0.0004 per leaf. Lower levels of parasitoid
caused mortality are progressively less effective;
88% mortality, for example, would allow the
whitefly population to reach 8.1 nymphs per leaf,
an unacceptably high level. Thus small differ-
ences in parasitoid-caused mortality in the range
observed (88-99%) are critically important in the
success or failure of whitefly biological control in
commercial crops.
Because differences in mortality rates interact
with variation in realized fecundity and sex ratio
in ways that cannot be easily predicted, to actu-
ally know how well a given parasitoid release rate
or pattern works in limiting final whitefly densi-
ties, tests must be rigorously conducted under
commercial conditions where this technology will
be ultimately utilized. In both summer stock
plants and fall Christmas crop plants,E. eremicus
at 3 females per plant per week effectively sup-
pressed silverleaf whitefly (Hoddle & Van Drie-
sche 1999ab). Poinsettias at the end of the crop
were acceptable to growers as a source of cuttings
or, for the Christmas crop, for sale to retailers
(with fewer than 2 live nymphs and pupae per
leaf). This commercially acceptable level of con-
trol was not achieved with the same release rates
of E. formosa Beltsville. This release rate, how-
ever, was too expensive for grower adoption. Con-


sequently, we chose to investigate whether or not
the pattern of parasitoid releases, independent of
number released, might be manipulated in ways
that increased the level of parasitoid impact on
whitefly populations.
We hypothesized that release patterns that
concentrated parasitoid releases either in the
early or late part of the crop cycle might be more
effective for controlling B. argentifolii. In small
greenhouses, we tested two variable-rate release
patterns against a fixed weekly release rate of 3
females per plant. In pattern 1 ("low-high"), par-
asitoids were released at a low rate in the first
half of the crop and then the number was in-
creased once plants were larger (first 1, then 5
parasitoids per plant per week) and in pattern 2
("high-low") this pattern was reversed (first 5 par-
asitoids per plant, then 1 in the second half of the
crop cycle), concentrating highest parasitoid
numbers on the smallest plants, early in the crop.
The argument for potential greater efficacy of
release pattern 1 (low-high) was that, since para-
sitoid foraging efficiency declines as plant size in-
creases (Hoddle et al. 1998), increasing parasitoid
release rate in the later part of the crop when
plants are largest might compensate for this de-
cline in per parasitoid efficacy. Also, at lower re-
lease rates progeny production by E. eremicus
within the greenhouse increases because fewer
parasitized hosts die from multiple ovipositions
and host feeding (see Hoddle 2000 for a review of
this argument). The argument for greater efficacy
of release pattern 2 (high-low) was that using
higher release rates when plants were small
might virtually exterminate the whitefly popula-
tion, leaving too little time before crop sale for
whiteflies to recover to damaging levels.
In fall 1995, we ran a trial withE. eremicus in
small greenhouses (holding 90 plants) (Hoddle et
al. 1999) to test the pest control value of these
variable release patterns. We found that pattern
2 (high-low) resulted in 75% fewer live whitefly
nymphs and pupae per plant at the end of the
crop (week 14) than did pattern 1 (low-high) (Hod-
dle et al. 1999).
The main goal of the study presented here was
to directly compare, under fully realistic produc-
tion conditions, the better of these two variable
E. eremicus release patterns (high-low) directly
against the fixed released pattern. By design
these two treatments have the same release rate
of E. eremicus, allowing us to isolate any effects
due to the single factor of parasitoid release pat-
tern. We also took advantage of available green-
houses in this same trial to pursue a second goal,
to assess the efficacy of a low release rate (one
parasitoid per plant per week) of E. formosa. We
did this because (1) the low rate of this species did
perform reasonably well (causing 95% mortality)
in earlier small greenhouse trials; (2) published
work indicated that this parasitoid when used at


March 2001







Van Driesche et al.: Efficacy of Variable and Fixed Parasitoid Rates


low rates might actually be more, not less, effec-
tive than high rates due to the effects of mutual
interference among parasitoids (Hoddle et al.
1997a; Hoddle 2000); and (3) producers recom-
mend use of low release rates of the species in Eu-
ropean flower crops, but few trials in North
America exist to support this recommendation.

MATERIALS AND METHODS

Study Site and Experimental Design

The study was conducted in commercial green-
houses in western Massachusetts (Fairview
Farms, Whately, MA), for seventeen weeks be-
tween 15 August and 6 December, 1996. Six plas-
tic hoop houses (each identical in size and
construction, with dimensions of 4.8 x 29.3 m)
were used for the principal treatments.
Three treatments were examined, each ran-
domly assigned to a whole greenhouse with two
replications: (1) a fixed release rate of three fe-
males of E. eremicus per plant per week; (2) a
variable release of E. eremicus, with five females
released per plant per week for the first eight
weeks of the trial (August 16-October 4) and one
female per plant per week for the last nine weeks
(October 11 to December 6); and (3) the commer-
cial strain of E. formosa released at one female
per plant per week A seventh greenhouse, in
which the grower used pesticides for whitefly
management, was also examined 12 times be-
tween 26 August to 18 November to provide a fur-
ther comparison to whitefly suppression levels
seen in the biological control treatments.
In each test greenhouse (except for the chemi-
cal control greenhouse), two cages (95 pm mesh
over PVC frames with dimensions 153 x 92 x 117
cm) were used to isolate five pots, each with three
poinsettia plants, as controls. One cage in each
greenhouse (designated "control for treatment")
received no treatments of any kind to suppress
whiteflies. The other cage (designated "control for
caging effect") received the same parasitoid treat-
ment as the greenhouse in which it was placed.
Initial densities of whitefly nymphs and pupae in
cages were manipulated to match those in test
greenhouses (see below).

Crop Composition and Management

In each greenhouse, a poinsettia crop was es-
tablished on August 15, 1996 using 1500 plants,
all 'Freedom' varieties (1140 red, 200 white and
160 pink per house) from Paul Ecke Ranch (En-
cinitas, CA). These plants were planted in soil-
less media, three stems per 20-cm dia pot. Num-
bers of plants in each house remained constant
until November 27, at which time removal of col-
ored plants for Christmas sale began. Numbers of
parasitoids released during the last three weeks


of the trial were reduced as needed to keep the
parasitoid release rate per plant constant. Plants
placed in cages were selected from plants in each
test greenhouse at the start of the experiment,
choosing plants so that the average density of
whitefly nymphs on plants put in cages was the
same as that of the whole greenhouse.
All whiteflies found on plants were B. argenti-
folii and were assumed to have entered the green-
houses on leaves of rooted cuttings purchased
from suppliers.
All plants in all greenhouses were treated with
the fungicide thiophanate methyl+etridiazole
(Banrot 40WP, Scotts Sierra Crop Protection
Co., 1411 Scottslawn Rd., Marysville, OH 43041)
to control root rot on 18 August and 21 September.
Plants in the chemical control greenhouse were
treated with imidacloprid (Marathon@) on 12
September. No insecticides were used in any of
the six test greenhouses, except in one of the two
greenhouses in which E. formosa was released. In
this single greenhouse, insecticide smokes (Fulex
Dithio, sulfotep, Fuller Systems, Inc., Woburn,
MA 01801) were applied on 14 and 27 November
to reduce numbers of adult whiteflies before sale.

Population Sampling

Whitefly densities in each of the six test green-
houses at the start of the trial were determined
by examining all the leaves of 100 freshly potted
cuttings with a 3.5x head-mounted magnifying
device. All live whitefly nymphs, pupae or adults
were counted. Because initial whitefly densities
were extremely low (0.0083 live stages per cut-
ting), cohorts of B. argentifolii nymphs were cre-
ated using a laboratory colony and infested plants
were placed in each house to augment the popula-
tion by an estimated 1.0 nymph per plant (=1500
B. argentifolii nymphs added per greenhouse). To
achieve this, six infested plants were introduced
into each greenhouse. Each infested plant had
three leaves on which cohorts of B. argentifolii
nymphs had been created by using leaf cages to
confine groups of 5-6 pairs of adult whiteflies.
Each cohort initially consisted of 105 eggs. Previ-
ous lifetable estimates (Hoddle et al. 1997abc)
suggest that 80% of these eggs would hatch and
this method was thus equivalent to adding 1512
nymphs per house. Plants were placed in green-
houses on 19 August and leaf cages were immedi-
ately removed from one infested leaf per plant.
Leaf cages were removed from the second and
third leaves on each infested plant on August 23
and 29. Staggered removal of leaf cages was in-
tended to promote whitefly survival and enhance
the establishment of a whitefly population de-
spite ongoing parasitoid releases. In each of the
control cages in each test greenhouse, one plant
with one infested leaf bearing 19 eggs was added
(being the equivalent of 15 nymphs, allowing for







Florida Entomologist 84(1)


the estimated 80% hatch). Cages thus received
the same increase of one nymph per plant as did
the whole greenhouses.
Growth of whitefly populations in test green-
houses and cages was measured by counting
whiteflies on each of 3 leaves (one lower, one mid-
dle and one upper) on each of 90 randomly se-
lected plants each week from each greenhouse. In
cages, 8 plants were chosen at random for sam-
pling, resulting in 24 leaves being examined per
cage per week. Sampling was nondestructive,
with whitefly numbers being counted with the aid
a head mounted optical magnifier, as with the
counts on cuttings. For each leaf, numbers were
recorded of live nymphs, live pupae, dead nymphs,
dead pupae, parasitized nymphs, whitefly pupal
exuviae, whitefly exuviae bearing parasitoid emer-
gence holes, and adult whiteflies.
Parasitoid Sources and Sampling
Eretmocerus eremicus. This parasitoid was ini-
tially supplied by Beneficial Insectary (Oak Run,
CA) and after week 7 by Koppert Biological Sys-
tems, Inc. (Berkel en Rodenrijs, The Netherlands,
through the North American office in Romulus,
MI). Eretmocerus eremicus was received as loose
parasitized Trialeurodes vaporariorum (Westwood)
nymphs from the supplier and the number needed
for release was calculated by assuming a 60%
emergence rate and a 50/50 sex ratio (as deter-
mined in other trials, Hoddle & Van Driesche
1999b; Van Driesche et al. 1999). We weighed 10
aliquots of parasitized nymphs to estimate the
number of parasitoid pupae in 0.02 g. We then
weighed the quantity of parasitized T vaporari-
orum nymphs needed to treat greenhouses or
cages in view of plant number present and de-
sired parasitoid release rate. Actual emergence
rates and sex ratios were measured in the course
of the trial (see below) and used to calculate the
actual release rate achieved.
Eretmocerus eremicus was deployed by placing
parasitized T vaporariorum nymphs (not glued to
cards) in styrofoam release cups (6 cm tall, 5.5 cm
wide at bottom, 8.5 cm wide at top), which had the
bottoms cut out and replaced with organdy (mesh
0.9 pm) to allow for drainage. Cups were attached
10 cm above the canopy to wooden stakes (50 cm
long) placed in the potting media. In each biologi-
cal control greenhouse receiving this parasitoid,
there were 15 release cups distributed evenly
throughout the crop. Since watering was done via
overhead hoses, workers were asked to avoid wet-
ting release cups.
Encarsia formosa. This thelytokous parasitoid
species was supplied by Applied Bionomics (Sid-
ney, BC, Canada) as parasitized fourth instar
nymphs of T vaporariorum glued to release cards,
with 200 parasitoids per card. Based on earlier
trials and producer's advice, we assumed that
50% of pupae would emerge as adults. Numbers


of cards needed per greenhouse were then calcu-
lated using these estimates of numbers per card,
the emergence rate, and the number of plants per
greenhouse or cage.
Encarsia formosa were deployed in green-
houses by hanging the necessary number of man-
ufacturer's release cards (15 per greenhouse)
(bearing parasitized T vaporariorum nymphs) on
plants throughout the crop.
Verification of Release Rates. To verify our as-
sumptions concerning the adult emergence rates
for each parasitoid species, percentage emergence
of pupae of each parasitoid species was deter-
mined weekly throughout the trial. No parasi-
toids emerged from our shipments before being
placed in the test greenhouses. In each green-
house, emergence cards (forE. formosa) or release
cups (for E. eremicus) were collected and taken
back to the laboratory after a one week exposure
in the test greenhouses. For each parasitoid spe-
cies, one hundred and fifty whitefly nymphal ca-
davers were selected randomly from the material
on the release card or in the release cups and the
number of successfully emerged parasitoids was
determined based on observation of parasitoid
emergence holes.
The proportion of emerging adults of E. ere-
micus that were female was determined on eight
dates throughout the test. On each date, 100-200
pupae were removed from orders received from
suppliers and held in the laboratory in glass vials
at 22C for emergence. Seven to ten days later, one
hundred adults were randomly selected and sexed.
Information on emergence rate, sex ratio (E.
eremicus only), and number of pupae placed in
greenhouses was used to calculate the release
rate achieved in each greenhouse in each week.
Statistical Analysis
The densities of live whitefly nymphs per leaf
at harvest were compared among treatments
with a nested ANOVA and treatment means sep-
arated by use of Tukey's studentized mean sepa-
ration test (at P = 0.05).

RESULTS
Release Rates of Parasitoids and Quality Control
Eretmocerus eremicus. Parasitoid emergence,
summed over all dates within each greenhouse,
varied among greenhouses from 46.1-58.2% and
averaged 53.5% + 1.9 (SE) overall. The percent-
age of adult E. eremicus emerging from pupae
held after receipt in the laboratory that were fe-
male ranged among dates from 39 to 58%. The
seasonal average, based on 800 parasitoids, was
48.1% + 2.2 (SE).
Because the proportion of E. eremicus that
emerged successfully (53.5%) was less than what
we assumed (60%), insufficient pupae were placed
in some greenhouses on some dates to achieve the


March 2001







Van Driesche et al.: Efficacy of Variable and Fixed Parasitoid Rates


intended release rate. Actual release rates (fe-
males parasitoids per plant per week) averaged
3.8 (replicate one, 3.1 0.6; replicate two, 4.4 +
0.6) and 0.8 (replicate one, 0.8 + 0.5; replicate two,
0.8 0.7) for the variable release rate treatment
and 2.8 (replicate one, 2.7 0.2; replicate two, 2.8
+ 0.2) for the fixed rate, rather than 5 and 1, and
3 as intended (Fig. 1).
Encarsia formosa. The commercial strain of E.
formosa had seasonal average emergence rates of
44.9 and 44.5% for the two test greenhouses, for a
grand seasonal average of 44.7 2.5 (SE). Num-
bers of pupae per card averaged 199.6 7.2 (SE).
Numbers of female parasitoids per plant actually
emerging in the greenhouse were 1.2 0.1 (SE) in
each test greenhouse.

Whitefly Population Trends in Caged Controls

Whitefly nymphal populations in cages in which
no treatments were made increased rapidly in
density after mid November in the four green-
houses receiving E. eremicus releases (Fig. 2A, B).
Whitefly nymphal populations in control cages in
the two greenhouses receiving E. formosa re-
leases increased in late November, but then de-
clined in December (Fig. 2C). In cages in which
E. eremicus releases were made (constant and










1-Aug 30-Aug 13-Sep 27 Sep 11 Oct 25-Oct 8Nov 22-No 6-Dec



B












o 1&Aug 30-Aug 13-Sep 27-Seov Il-O 25-Ot e-mw 22-N.o e-D.
Release Date

Fig. 1. Average release rates achieved (for two green-
enhses each): greenhouses receiving the high-low release
rate of Eretmocerus eremicus (first 5 females per plant
per week, then one female) (A); greenhouses receiving
the fixed release rate of E. eremicus (3 females per plant
per week) (B); greenhouses receiving a low release rate of
E. formosa (1 female per plant per week) (C).


I 25


-4-Co'tol Cag --S5 C


1 -Aug 2 .-Aug 12-S 2B-Sp 0-Oct 212Oct 7.2 w 21-.Nov 5.-D 1 -oD
Sample Wae,


10-
5-

1S-Ag 2a-Ag 12-Sp 2Sap t-pd D4t
Sample Dat-


1-.ug, 2 .ug S 2. X - 1 .I
Sample Drt

Fig. 2. Trends in average density of whitefly nymphs
for control cages (control cage and parasitoid cage) for
two greenhouses receiving the variable release rate of
Eretmocerus eremicus (first 5 females per plant per
week, then one female) (A); two greenhouses receiving
the fixed rate of E. eremicus (3 females per plant per
week) (B); two receiving the low rate of Encarsia for-
mosa (1 female per plant per week) (C).


variable), whitefly nymphal densities remained
below 1 nymph per leaf during this same period,
reflecting a high level of whitefly suppression
(Fig. 2A, B). In cages in which E. formosa was in-
troduced, nymphal densities in late November ex-
ceeded 4 nymphs per leaf (Fig. 2C). Comparison of
whitefly densities at harvest in cages with and
without parasitoid releases showed that nymphal
densities per leaf in control cages were reduced
99.9% by the fixed release rate treatment ofE. er-
emicus, compared to 96.8% for the variable (high-
low) release rate treatment of the same species
and 50.9% for the low release rate of E. formosa.

Whitefly Population and Parasitism Trends
in Trial Greenhouses

Whitefly populations outside of cages in test
greenhouses were low in all treatments and re-
mained so throughout the trial (Fig. 3A-E). Den-
sities of live nymphs remained below 1 nymph per
leaf in all test greenhouses except in one of the
two receiving releases of E. formosa (Fig. 3D), in


7-N 21-N. 5-D. I.-C







Florida Entomologist 84(1)


15-Aug 2Aug 12-Sep 2N-S.p 10-Od 24-Dc 7-Nov 21-NT 5-D-
.' o eB


-Aug 2 Ag 12.&p SlS 1p tO i0- 0tC 7-Na 21-NvJ 5-DBC

I.1 0

ia:[






15-Aug 2.-Au 12-,ep 2,-Sp 10-Gd 24-d 7-o 1 l.Nov 5- D-e ""








Fig. 3. Trends in density of whitefly nymphs per leaf
on plants in greenhouses receiving the variable release
rate of Eretmocerus eremicus (first 5 females per plant
per week, then one female) (A, average of two repli-
cates); the fixed release rate of E. eremicus (3 females
per plant per week) (B, average of two replicates); the
low rate of Encarsia formosa (1 female per plant per
week) (C, D, replicates different and presented sepa-
rately); or the chemically-treated greenhouse under
grower management (E, one replicate).


which increasing densities exceeded 2 nymphs
per leaf at harvest. Pupal and adult whitefly den-
sities in all greenhouses were lower than nymphal
densities, but followed similar trends, which are
not presented. The trend of quick increase in
whitefly nymphal numbers in one E. formosa
greenhouse (Fig. 3D) prompted the grower to ap-
ply insecticidal smokes (Fulex Dithio [sufotep])
to suppress whitefly adults on plants before sale.
Final densities of live nymphs per leaf were
significantly different at harvest among treat-
ments (F = 27.89, df =2, p = 0.0001) and whitefly
nymphal densities in the low rate of E. formosa
treatment were significantly higher than the two
E. eremicus treatments, which were statistically
similar. Whitefly densities in the chemical control
greenhouse were highly suppressed throughout
the trial.
Few parasitized whitefly nymphs were en-
countered in this trial in any of the test green-
houses and we were not able to draw any
inferences about the effect of the treatments on


parasitism rates. However, low parasitism rates
do not imply that total host mortality caused by
parasitoids was low. For these parasitoid species,
host feeding is often the major cause of host mor-
tality, especially when parasitoid-to-host ratios
are high, as would be the case in an augmentative
biological control program when hosts are scarce.
The effect of mortality from parasitoid host feed-
ing is reflected in lowered host density, which has
been analyzed above.

DISCUSSION

We had two objectives with this experiment:
(1) to determine if variable release rates of E. ere-
micus would be more effective than a fixed release
rate of the same total number of parasitoids re-
leased over a complete poinsettia cropping period
under commercial growing conditions and (2) to
ascertain if a low fixed weekly release rate of E.
formosa would suppress B. argentifolii densities on
poinsettia to acceptable levels at time of harvest.
In this trial, there were no statistical differ-
ences in whitefly nymphal densities at harvest
between greenhouses receiving fixed versus vari-
able rate releases of E. eremicus. While starting
whitefly densities in these greenhouses were very
low, whitefly populations in control cages (in
which E. eremicus was not applied) increased to
high levels (25-35 live nymphs per leaf) by har-
vest. The absence of such increase in the four E.
eremicus-release greenhouses (and their associ-
ated parasitoid-release cages) was thus due to
natural enemy activity. Based on (1) the lack of
evidence in this trial supporting the idea that a
variable rate increases control and (2) lack of any
such effect in a previous trial run in small green-
houses (Hoddle et al. 1999), we conclude that the
variable release pattern has no discernible ad-
vantage over a fixed release rate pattern and do
not recommend its use.
Encarsia formosa released at one parasitoid
per plant per week provided inconsistent whitefly
control. One of the two greenhouses receiving this
treatment developed an increasing whitefly popu-
lation that at harvest was still relatively low but
was increasing enough that the grower inter-
vened with chemical control measures. Because
low rates of E. formosa have failed to consistently
control B. argentifolii on poinsettia, we do not rec-
ommend use of this parasitoid on this crop in
North America.
This trial demonstrates that tactics other than
varying the release rates of E. eremicus will be
needed to make use of this parasitoid both eco-
nomical and effective. Insect growth regulators
found in the laboratory to be compatible with E.
eremicus (Hoddle et al. 2000) have enhanced the
economic feasibility of using this parasitoid in
greenhouses, allowing release rates to be reduced
by two thirds (Van Driesche et al. 2000).


March 2001







Van Driesche et al.: Efficacy of Variable and Fixed Parasitoid Rates


ACKNOWLEDGMENTS

We thank Judy Hunter and the owners of Fairview
Farms for permission to use their greenhouses and
crops for this experiment. We thank Beneficial Insec-
tary for providing part of the Eretmocerus eremicus
used in the experiment at reduced cost. Funding for the
work was provided by the Massachusetts IPM Program.

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BYRNE, D. N., T. S. BELLOWS, JR., AND M. P. PARRELLA.
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DROST, Y. C., A. FADL ELMULA, C. J. A. M. POSTHUMA-
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HODDLE, M. S., R. G. VAN DRIESCHE, AND J. SANDER-
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Florida Entomologist 84(1)


NEOTERMES PLATYFRONS, A NEW DAMPWOOD TERMITE
(ISOPTERA, KALOTERMITIDAE) FROM THE DOMINICAN REPUBLIC

JAN KRECEK AND RUDOLF H. SCHEFFRAHN
Fort Lauderdale Research and Education Center
University of Florida, Institute of Food and Agricultural Sciences
3205 College Avenue, Fort Lauderdale, FL 33314

ABSTRACT
Neotermes platyfrons n. sp. is described from the winged imago and the small and large soldier
castes. This species is endemic to Hispaniola and surveys of the Dominican Republic indicate
the greatest populations occur in the far-eastern coastal woodlands.

Key Words: new species, taxonomy, West Indies, Greater Antilles, Caribbean

RESUME
Neotermes platyfrons sp. n., es descrita basandose en los adults alados y las castas de sol-
dados grande y pequena. La nueva especie descrita es end6mica de la Espanola y nuestros
hallazgos sugieren que las mayores poblaciones se hallan en los bosques costeros del ex-
tremo oriental de la Isla.


Twenty-two species of Neotermes occur in the
Neotropical Region (Constantino 1998). Several
Neotermes spp. are common elements of the ter-
mite fauna of coastal woodland and mangrove
habitats in southern Florida and the West Indies
(Krecek et al. 2000; Scheffrahn et al. 1994; Schef-
frahn et al. 2000). While conducting termite sur-
veys in the Dominican Republic between 1992
and 1996, we collected numerous samples of a
Neotermes sp. that were preliminarily identified
as N. (=Kalotermes) jouteli (Banks) (Harris 1955,
1971; Scheffrahn et al. 1994). We now recognize
those specimens as a new species of Neotermes
that is described herein for the first time.

MATERIALS AND METHODS

The description of N. platyfrons n. sp. is based
on the examination of 27 colony samples, all in
authors' collection, taken from 13 localities in the
Dominican Republic (Fig. 1). Morphometric data
from specimens preserved in 85% ethanol were
obtained using a stereomicroscope fitted with an
ocular micrometer. Measurements were adopted
mainly from Roonwal (1970), while the color
scheme of Sands (1965) was used. The terms
"small" and "large" soldiers (Krishna 1961) are
equal to the terms "short-headed" and "long-
headed" soldiers (Banks & Snyder 1920), respec-
tively. These terms are used to separate the two
most common size morphs of soldiers occurring
within some species of the Kalotermitidae (Nickle
& Collins 1989).
Scanning electron micrographs (SEMs) were
digitized at 600 dpi, the digital image outline
traced using photograph-enhancing software


(Photo Magic, Micrografx, Inc., Richardson, TX),
the background converted to black, and the scale
bar digitally drawn. Collection localities were
mapped (Fig. 1) using ArcView GIS version 3.0a
software and relevant map data from Digital Map
of the World version 1.0 (Environmental Systems
Research Institute, Inc. Redlands, CA).
The holotype alate and a paratype soldier will
be deposited in the American Museum of Natural
History, New York. Additional paratype alates
and soldiers will be deposited in the National Mu-
seum of Natural History (Smithsonian Institu-
tion), Washington, DC, and in the Florida State
Collection of Arthropods, Florida Department of
Agriculture and Consumer Services, Division of
Plant Industry, Gainesville. Remaining paratypes
are maintained in the authors' collection at the
University of Florida Research and Education
Center, Fort Lauderdale, FL.

Neotermes platyfrons, New Species

Kalotermes near jouteli Banks; Harris 1955 (Do-
minican Republic)
Neotermes jouteli (Banks); Harris 1971 (Domini-
can Republic)
Neotermes jouteli (Banks); Scheffrahn et al. 1994
(Dominican Republic records only)

Imago (Fig. 2 A-B, Table 1).

In dorsal view, body almost uniformly ferrugi-
nous with exception of darker chestnut brown V-
shaped mark on frons and M-shaped mark on ver-
tex. Mandibles chestnut brown at bases, almost


March 2001







Krecek & Scheffrahn.: New Neotermes from the Dominican Republic


Fig. 1. Neotermes platyfrons localities and termite collection sites in the Dominican Republic from 1992-1996.


black distally. Anteclypeus pale yellow-orange.
Antennae ferruginous with exception of darker
chestnut-brown articles 2-4. Ocelli yellow-white,
coloration contrasts conspicuously with head cap-
sule. Pronotum chestnut-brown, periphery slightly
darker and concolorous with distinct chevron pat-
tern on wing scales of pterothorax. Femora pale
yellow; tibiae and tarsi ferruginous. Arolia whitish.
In dorsal view, head capsule suboval; in ventral
view, margins below eyes straight and convergent
anteriorly. Frons moderately rugose, flat, and
with shallow depression; surrounded on each side
by ridges extending from ocelli to dorsal mandib-
ular condyles. Frons rugosity terminates posteri-
orly as shallow median channel between ocelli. In
lateral view, angle of slope between planes of frons
and vertex = 10. Compound eyes large and pro-
truding, subcircular or very slightly subreniform;
margins along antennal sockets rectate or very
faintly concave. Ocelli moderately large and
slightly protruding, obliquely oval, and clearly
separated from eyes. Basal striations on mandi-
bles weak or absent. Epicranial depression weak
or absent. Head with scattered short and fewer
longer (= 0.2-mm-long) erect setae. Pronotum
with similar pilosity, but with proportionally more
longer setae than short setae along margins. Fore
wing scale and proximal portion of fore wing with
few short setae. Antennae with 18-20 articles,


usually 19; relative length formula 2 = 3 > 4 = 5 or
2 > 3 > 4 = 5. Pronotum robust, with anterior mar-
gin deeply concave and peripheral rim elevated;
median posterior margin faintly concave, and pos-
terior corners subtruncate. Subcosta of fore wing
closely parallels costal margin and joining costal
margin at 14 wing length from suture. Radius of
fore wing intersects costal margin near midwing,
and radial sector with 4-6 branches; branching
commences proximal to midwing. Sclerotized me-
dia of fore wing with several very faint diagonal
anterior branches intersecting radial sector, and
with posterior branches that fade into membrane
save one or two that reach wing margin. Wing
membrane texture with faint nodulations.

Comparisons.

Alates of Neotermes platyfrons are intermedi-
ate in size between those of the smaller N. jouteli
and the larger N. mona (Banks) with some over-
lapping measurements among the three species.
The most distinguishing range of measurements
for N. jouteli, N. platyfrons, and N. mona, respec-
tively, are as follows: head length to postclypeus
1.34-1.54, 1.55-1.68, and 1.63-1.97 mm; head
height without postmentum 0.88-1.05, 1.05-1.11,
and 1.11-1.21 mm; pronotum maximum length
1.06-1.32, 1.29-1.47, and 1.49-1.68 mm; pronotum







Florida Entomologist 84(1)


March 2001


Fig. 2. Scanning electron micrographs of Neotermes platyfrons: dorsal (A) and oblique (B) views of the imago
head, dorsal (C) and lateral (D) views of the small soldier head, and dorsal (E) and lateral (F) views of the large sol-
dier head. All specimens are from Punta Cana, La Altagracia Province, Dominican Republic. Antennae and palpi
partially removed for clarity. Scale bar equals 1 mm.


maximum width 1.75-2.05, 2.00-2.22, and 2.22-
2.47 mm, and head maximum width at eyes 1.59-
1.81, 1.83-1.93, and 2.00-2.17 mm.


The distinct and darkened V- and M-shaped
markings on the N. platyfrons imago head are ab-
sent onN. jouteli head. The long setae on the head







Krecek & Scheffrahn.: New Neotermes from the Dominican Republic


TABLE 1. MEASUREMENTS OF NEOTERMES PLATYFRONS IMAGO.

Measurement in mm
(n = 6 males, 6 females from 4 colonies) Range Mean + S.D. Holotype

Head length with labrum 1.91-2.20 2.03 + 0.11 1.95
Head length to postclypeus 1.55-1.68 1.60 + 0.037 1.55
Head width, maximum at eyes 1.83-1.93 1.89 + 0.029 1.83
Head height without postmentum 1.05-1.11 1.07 + 0.018 1.08
Labrum width, maximum 0.67-0.77 0.72 + 0.031 0.74
Eye diameter with sclerite, maximum 0.59-0.64 0.62 + 0.015 0.63
Eye to head base, minimum from sclerite 0.25-0.32 0.32 + 0.020 0.29
Ocellus diameter, maximum 0.19-0.25 0.22 + 0.020 0.23
Ocellus diameter, minimum 0.15-0.18 0.16 + 0.010 0.16
Eye sclerite to ocellus, minimum 0.01-0.06 0.03 + 0.014 0.02
Pronotum, maximum length 1.29-1.47 1.40 + 0.052 1.39
Pronotum, maximum width 2.00-2.22 2.08 + 0.061 2.07
Total length with wings 16.47-18.74 17.76 + 0.82 17.61
Total length without wings 7.95-10.22 9.06 + 0.65 8.52
Fore wing length from suture 12.78-14.34 13.64 + 0.51 13.49
Fore wing, maximum width 3.40-3.79 3.55 + 0.13 3.43



and pronotum of N. platyfrons are about 0.2 mm tened and rugose while that of N. castaneus is
long while those of N. jouteli are >5x shorter. The convex and smooth.
shallow depression centered at the intersection of
the epicranial suture in N. jouteli and N. mona is Soldier. (Figs. 2 C-F, Tables 2-3).
faint or absent inN. platyfrons. The anterior mar-
gin of the pronotum is more concave in N. platy- Beyond size differences given in Tables 2 and
frons than in N. jouteli. The posterior corners of 3, soldier caste dimorphism of this species is less
the N. platyfrons pronotum are subtruncate, distinctive when compared with some congeners.
while in N. mona they are more rounded and Consequently, the large and small soldier morphs
more pilose. are described together.
The imago of the sympatricN. castaneus (Bur- In dorsal view, head capsule, distal antenna
meister) is unlike that of N. platyfrons. The gen- articles, and labrum ferruginous except for chest-
eral color of the former is castaneous, while that nut brown anterior frons, postclypeus, frontal and
of N. platyfrons is orange. The eyes of N. platy- antennal carinae, and 4 proximal antennal arti-
frons are ~1.5x larger in diameter than those of cles. Anteclypeus yellowish-white. Thorax and ab-
N. castaneus, and the frons of N. platyfrons is flat- dominal dorsum ferruginous orange. Mandibles


TABLE 2. MEASUREMENTS OF NEOTERMES PLATYFRONS SMALL SOLDIER.

Measurement in mm (n = 13 from 11 colonies) Range Mean + S.D.

Head length to tip of mandibles 3.86-4.31 4.13 + 0.16
Head length to postclypeus 2.57-3.02 2.85 + 0.15
Head width, maximum 2.00-2.30 2.14 + 0.077
Antennal carinae, outside span 1.78-2.03 1.92 + 0.072
Head height, excluding postmentum 1.52-1.73 1.62 + 0.072
Labrum, maximum width 0.51-0.60 0.55 + 0.030
Postclypeus width, maximum 0.72-0.87 0.80 + 0.042
Left mandible length, tip to most distant visible point of ventral condyle 1.89-2.01 1.97 + 0.031
Postmentum, length in middle 1.68-2.14 1.91 + 0.14
Postmentum, maximum width 0.72-0.83 0.77 0.036
Postmentum, minimum width 0.38-0.47 0.43 0.035
Pronotum, maximum width 2.30-2.52 2.39 + 0.083
Pronotum, maximum length 1.22-1.50 1.36 + 0.095
Hind tibia length 1.29-1.64 1.44 0.096
Total length 8.66-10.93 9.98 0.75







Florida Entomologist 84(1)


TABLE 3. MEASUREMENTS OF NEOTERMES PLATYFRONS LARGE SOLDIER.

Measurement in mm (n = 10 from 8 colonies) Range Mean + S.D.

Head length to tip of mandibles 4.63-5.43 4.97+ 0.26
Head length to postclypeus 3.22-3.96 3.58 + 0.24
Head width, maximum 2.17-2.59 2.34 + 0.13
Antennal carinae, outside span 2.00-2.39 2.18 + 0.12
Head height, excluding postmentum 1.75-1.95 1.85 + 0.074
Labrum, maximum width 0.52-0.64 0.58 + 0.033
Postclypeus width, maximum 0.83-0.95 0.89 + 0.040
Left mandible length, tip to most distant visible point of ventral condyle 2.05-2.30 2.17 + 0.078
Postmentum, length in middle 2.41-2.77 2.55 + 0.11
Postmentum, maximum width 0.83-0.95 0.87 + 0.034
Postmentum, minimum width 0.44-0.52 0.48 + 0.030
Pronotum, maximum width 2.47-3.13 2.76+ 0.17
Pronotum, maximum length 1.38-1.71 1.57 + 0.11
Hind tibia length 1.52-1.70 1.63 + 0.071
Total length 8.66-13.35 10.91+ 1.25


glossy, almost black except for very dark chestnut
brown bases. Epicranial sutures faint. Eyes
blackish or fainter dark pigmentation. Femora
yellowish-white; tibiae pale ferruginous. Sternum
pale ferruginous orange. Ferruginous postmen-
tum contrasting with pale ferruginous orange ge-
nae. Large soldiers are slightly more pigmented
than small soldiers.
In dorsal view, head capsule moderately elon-
gate in small soldier; relatively more elongated in
large soldier. Sides of head subparallel. In small
soldier, sides faintly convex or converging to ante-
rior; in large soldier, sides usually very faintly con-
cave to middle. Head capsule with posterior
corners evenly rounded; posterior margin narrowly
rectate in small soldier, widely rectate in large sol-
dier. Head capsule and pronotum relatively
densely covered with = 0.1-mm-long setae. Frons
depressed or slightly concave. Frontal carinae each
with small conical tubercle. Labrum, when ex-
posed, linguiform. Mandibles robust; in large sol-
dier slightly more stout than in small soldier; bases
faintly humped and with few minute setae on large
soldier; left apical tooth hooked = 60, dentition
conspicuous. Antennae with 14-16 articles in small
soldier, usually 14-15; 13-16 in large soldier, usu-
ally 15-16; relative length formula 2 < 3 > 4 = 5.
Third antennal article subclavate, proximal arti-
cles moniliform, distal articles slightly elongate.
Pronotum large and relatively short, noticeably
wider than head capsule. Anterior margin of prono-
tum broadly and shallowly concave; lateral mar-
gins convex; posterior margin widely subrectate,
usually with very faint median emargination.
In lateral view, head capsule slightly dorso-
ventrally flattened. Plane of frons slopes = 20 be-
low plane of vertex in small soldiers;= 30 in large
soldiers. Eyes oval. Mandibles moderately curved
upward in lateral view. Femora moderately broad
in small soldier; noticeably swollen in large soldier.


Comparisons.

Morphometric differentiation of the small sol-
diers of Neotermes platyfrons and N. jouteli is
very tenuous although hind tibia lengths are
1.29-1.64 mm and 1.54-1.72 mm, respectively.
Less character overlap occurs in large soldiers
but this morph is also difficult to differentiate by
measurements. The maximum pronotum lengths
of large soldiers range from 1.38-1.71 mm in N.
platyfrons and 1.71-1.85 mm inN. jouteli, and the
hind tibia lengths are 1.52-1.70 mm and 1.68-1.93
mm, respectively.
Both soldier morphs of N. platyfrons differ
from those of N. jouteli with the former having
proportionally more elongate head capsules and
mandibles (e.g., head length/maximum head width
ratio in minor soldiers is 1.35 inN. platyfrons and
1.2 in N. jouteli). The left apical tooth of N. platy-
frons is noticeably hooked, while in N. jouteli it is
only faintly hooked. The labrum ofN. platyfrons is
apically rounded while subtruncate in N. jouteli.
Basal mandibular pilosity in N. platyfrons is al-
most absent while well developed in N. jouteli.
Compared to the sympatric N. mona, both
small and large soldiers of N. platyfrons are
smaller in the following respective measurements
(mm): outer span of antennal carinae (small sol-
diers 2.18-2.80 vs. 1.78-2.03 and large soldiers
2.57-3.10 vs. 2.00-2.39), labrum maximum width
(small 0.64-0.87 vs. 0.51-0.60 and large 0.72-0.83
vs. 0.52-0.64), left mandible length (small 2.24-
2.84 vs. 1.89-2.01 and large 2.67-3.07 vs. 2.05-
2.30), pronotum maximum length (small 1.63-
2.02 vs. 1.22-1.50 and large 2.00-2.37 vs. 1.38-
1.71), and pronotum maximum width (small 2.73-
3.28 vs. 2.30-2.52 and large 3.37-3.96 vs. 2.47-
3.13). The soldier head capsule, including the
postmentum, pronotum, and legs of N. mona, is
more pilose than those ofN. platyfrons.


March 2001







Krecek & Scheffrahn.: New Neotermes from the Dominican Republic


Both soldier morphs of N. platyfrons differ
with those of the sympatric N. castaneus consid-
erably. The N. castaneus soldier is significantly
larger than that ofN. platyfrons. The N. castaneus
soldier has unpigmented eye spots, while the eyes
of N. platyfrons are pigmented. The mandibles of
N. castaneus are distinctly paler proximally than
distally, while those of N. platyfrons are almost
concolorous throughout.

Etymology.

The species name is derived from the Greek
"platys" which refers to the depressed or rather
planer character of the frons in imagos and sol-
diers.

Type Material.

Holotype. Dominican Republic. La Altagra-
cia Province, 2.6 km S.W. of Punta Cana,
18.533N 68.368W, 6-XI-1996, J. Chase & J. Kre-
cek, 1 male holotype alate, 5 paratype alates, 3
paratype small soldiers and 3 paratype large sol-
diers (DR 1480). Additional specimens from this
colony used for SEMs (Fig. 2).
Paratypes. Dominican Republic. La Altagra-
cia Province, 4.4 km N.W. of Boca de Yuma,
18.392N 68.647W, 5-XI-1996, J. Chase & J. Kre-
cek, 2 alates, 1 small soldier, 1 large soldier (DR
1378); 1 km N.W. of Playa Bavaro, 18.665N
68.409W, 5-XI-1996, J. Chase & J. Krecek, 1
small soldier (DR 1389); 1 km W. of Playa Domini-
cus, 18.366N 68.831W, 6-XI-1996, J. Chase &
J. Krecek, 1 large soldier (DR 1409); same data, 1
small soldier (DR 1410); 0.5 km W. of Club Med.,
18.554N 68.353W, 6-XI-1996, J. Chase & J. Kre-
cek, 1 small soldier, 1 large soldier (DR 1448);
Bejucal, 18.667N 68.867W, 10-VI-1992, R. Schef-
frahn, J. Chase, J. Mangold, and J. de la Rosa, 1
small soldier, 1 large soldier (DR 504); Bavaro,
18.683N 68.433W, 11-VI-1992, R. Scheffrahn, J.
Chase, J. Mangold, and J. de la Rosa, 1 small sol-
dier (DR 512); Juanillo, 18.483N 68.417W, 11-
VI-1992, R. Scheffrahn, J. Chase, J. Mangold, and
J. de la Rosa, 1 small soldier (DR 567); Playa
Bavaro, 18.683N 68.767W, 1-IV-1993, J. Chase &
J. de la Rosa, 1 large soldier (DR 827); Barahona
Province, Camino a Santa Elena, 18.167N
71.133W, 30-III-1993, J. Chase & J. de la Rosa, 2
alates, 1 small soldier, 1 large soldier (DR 793);
Maria Trinidad Sanchez Province, Cabo Frances,
19.667N 69.950W, 9-VIII-1992, J. Chase, 2
alates, 1 small soldier, 1 large soldier (DR 682).
Additional Material Examined. Same data as
DR 512 above, 1 small soldier (DR 514), 1 small
soldier each (DR 526 and DR 538); same data as
DR 682, 1 small soldier (DR 680); same data as
DR 1378, 1 small soldier, 1 large soldier (DR 1379),
1 large soldier (DR 1380); same data as DR 1448,


1 small soldier, 1 large soldier (DR 1445), 1 small
soldier, 1 large soldier (DR 1446), 1 queen (DR
1449); same data as DR 1480, 1 small soldier (DR
1481), and 1 small soldier, 1 large soldier (DR
1482); La Altagracia Province, 0.5 km E. of Playa
Bayahibe, 18.372N 68.839W, 6-VI-1992, J. Chase
& J. de la Rosa, 1 king, 1 queen (DR 1423).

DISCUSSION

We postulate that N. platyfrons was first listed
as N. (=K.) jouteli by Harris (1955) in an inter-
cepted wood shipment from the Dominican Re-
public to England. Harris (1971), Araujo (1977),
and Scheffrahn et al. (1994) also accepted this ini-
tial determination. Based on current records, N.
castaneus, N. mona, and N. platyfrons are the
only Neotermes recorded from the Dominican Re-
public. Collections of N. platyfrons have been
most prominent in extreme eastern Dominican
Republic although two remote locations, one
southwestern and one north-central, have also
yielded specimens (Fig. 1).Neotermes mona has a
broader distribution in the Dominican Republic
(Krecek et al. 2000) that encompasses the distri-
bution of N. platyfrons in the extreme east. The
distribution ofN. castaneus in the Dominican Re-
public is also more widespread thanN. platyfrons,
but these two species have only been recorded to
be sympatric near Barahona. Except for the first
few instars, all castes of N. platyfrons exhibit
some degree of wing bud formation.

ACKNOWLEDGMENTS

The authors thank James A. Chase, John R.
Mangold, and Julian de la Rosa Guzman for field collec-
tions; Diann Achor, University of Florida, Lake Alfred
Citrus Research and Education Center, for her assis-
tance with scanning electron microscopy; and R. Giblin-
Davis and F. W. Howard, University of Florida, for their
critical reviews of this manuscript. Florida Agricultural
Experiment Station Journal Series No. R-07328.

REFERENCES CITED

ARAUJO, R. L. 1977. Catalogo dos Isoptera do Novo
Mundo. Academia Brasileira de Ciencias, Rio de Ja-
neiro, Brazil. 92 pp.
BANKS, N., AND T. E. SNYDER. 1920. A revision of the
Nearctic termites with notes on biology and geo-
graphic distribution. Bull. U.S. Nat. Hist. Mus.
Washington 108: 1-228.
CONSTANTINO, R. 1998. Catalog of the living termites of
the New World (Insecta: Isoptera). Arq. Zool. (Sao
Paulo) 35: 135-231.
HARRIS, W. V. 1955. Exhibit of living Kalotermes near
jouteli and preserved Zootermopsis angusticollis
from imported timber. Proc. R. Ent. Soc. London C,
20: 36-37.
HARRIS, W. V. 1971. Termites. Their recognition and con-
trol, 2nd ed. Longman Group, London. i-xiii + 186 pp.







76 Florida Ento



KRISHNA, K. 1961. A generic revision and phylogenetic
study of the Family Kalotermitidae (Isoptera). Bull.
American Mus. Nat. Hist. 122: 303-408.
KRECEK, J., N. Y. SU, AND R. H. SCHEFFRAHN. 2000.
Redescription of Neotermes mona, a dampwood ter-
mite (Isoptera, Kalotermitidae) from the central
West Indies. Fla. Entomol. 83: 268-275.
NICKLE, D. A., AND M. S. COLLINS. 1989. Key to the Kal-
otermitidae of eastern United States with a new
Neotermes from Florida. Proc. Entomol. Soc. Wash-
ington 91: 269-285.
ROONWAL, M. L. 1970. Measurements of termites (Isop-
tera) for taxonomic purposes. J. Zool. Soc. India 21:
9-66.


Im


ologist 84(1) March 2001



SANDS, W. A. 1965. A revision of the termite subfamily
Nasutitermitinae (Isoptera, Termitidae) from the
Ethiopian Region. Bull. British Mus. Nat. Hist.,
Entomol. Suppl. 4: 1-172.
SCHEFFRAHN, R. H, J. P. E. C. DARLINGTON, M. S. COL-
LINS, J. KRECEK, AND N.-Y. SU. 1994. Termites
(Isoptera: Kalotermitidae, Rhinotermitidae, Termi-
tidae) of the West Indies. Sociobiology 24: 213-238.
SCHEFFRAHN, R. H., J. KRECEK AND N.-Y. Su. 2000.
Redescription of the dampwood termites Neotermes
jouteli and N. luykxi (Isoptera: Kalotermitidae) from
Florida, Cuba, Bahamas, and Turks and Caicos.
Ann. Entomol. Soc. Am. 93: 785-794.







Meagher: Effect of Trap Color In FAW Capture


COLLECTION OF FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE) ADULTS
AND NONTARGET HYMENOPTERA IN DIFFERENT COLORED UNITRAPS

ROBERT L. MEAGHER, JR.
Center for Medical, Agricultural and Veterinary Entomology
Agricultural Research Service, U.S. Department of Agriculture, Gainesville, FL 32604

ABSTRACT

Field experiments were conducted to determine the effectiveness of different colored phero-
mone-baited traps in capture of Fall Armyworm, Spodoptera frugiperda, males and nontar-
get Hymenoptera. Plastic Universal Moth Traps (Unitraps) of different colors were baited
with commercial sex pheromone and were placed in peanut and corn fields in northern Flor-
ida. In one study, standard-colored (green canopy, yellow funnel, white bucket) traps col-
lected more moths than all-white or all-green traps. More Sphecoidea were found in white
traps while more Vespoidea were collected in standard traps. In another study, trap capture
was compared among standard, all-white, and standard traps with buckets painted two dif-
ferent yellow colors. Results showed that there were few differences in capture among traps
with different colors, however, contrasts between traps with yellow buckets or traps with
white buckets suggested more moths could be captured in yellow-bucket traps. Very few Hy-
menoptera were collected, although more Apoidea were found in white traps.

Key Words: insect behavior, Spodoptera, monitoring, pheromone traps, Hymenoptera

RESUME

Experimentos de campo fueron conducidos para determinar la efectividad de trampas de dis-
tintos colors con senuelo de feromona para capturar al machos del gusano Spodoptera fru-
giperda, y miembros de Himen6ptera. Trampas Plasticas Universales de Mariposa
(Unitraps) de colors diferentes fueron preparadas con seinuelo de feromona commercial de
sexo y colocadas en campos de maiz y mani en el norte de Florida. En un studio, trampas
de color estandar (toldo verde, embudo amarillo, cubeta blanca) colectaron mas mariposas
que trampas de color blanco o verde solamente. Mas Sphecoidea fueron encontrados en
trampas blancas mientras que mas Vespoidea fueron colectados en trampas estandar. En
otro studio, capture por trampa fue comparada entire estandar, blanca, y trampas estandar
con cubetas pintadas con dos colors amarillos diferentes. Los resultados demuestran que
hubo poca diferencia en captures entire trampas con diferentes colors, sin embargo, contras-
tes entire trampas con cubetas amarillas o trampas con cubetas blancas sugirieron que mas
mariposas pueden ser capturadas con trampas de cubeta amarilla. Muy pocos Himen6ptera
fueron colectados, aunque mas Apoidea fueron encontrados en trampas blancas.


Traps for insect pests can be categorized into
those that catch insects randomly (interception or
passive traps such as Malaise, sticky pane, or pit-
fall traps) and those that attract and elicit orien-
tating behavior (active traps such as light or
baited traps) (Southwood 1978). Traps that at-
tract insects use visual cues (yellow sticky cards,
yellow pans, red spheres, etc.), chemical cues
(pheromones, kairomones), edible baits, or any
combination of the three. Workers involved in
pest management research have developed traps
that combine visual and chemical cues to attract
insects, such as the work conducted with tephrit-
ids (Robacker et al. 1990, Stark & Vargas 1992,
Epsky et al. 1995).
Few studies have documented the influence of
visual cues in monitoring of noctuid moths. De-
coys (dead female moths) were shown to improve
capture of Helicoverpa zea (Boddie) males in elec-
trocutor grid and sticky traps (Gross et al. 1983).


Trap color has been shown to be important in the
collection of several noctuids such as Heliothis
virescens (F.) (Hendricks et al. 1972), Anticarsia
gemmatalis Hiibner (Mitchell et al. 1989),Agrotis
ipsilon (Hufnagel), and Pseudaletia unipuncta
(Haworth) (Hendrix & Showers 1990). Plastic
bucket traps with green canopies, yellow funnels,
and white buckets collected more Spodoptera spp.
males than all-green traps in several studies
(Mitchell et al. 1989; Pair et al. 1989; Lopez 1998).
All-white traps are also commercially available,
but have not been bioassayed for Fall Armyworm,
S. frugiperda (J. E. Smith) capture. My studies
were designed to compare capture of Fall Army-
worm males using the same chemical cue (com-
mercially available sex pheromone) but different
visual cues (trap colors).
Few studies have documented the species and
number of nontarget Hymenoptera that are cap-
tured in traps intended for agricultural lepi-







Florida Entomologist 84(1)


dopteran pests. Meagher & Mitchell (1999) found
species from Apoidea, Pompiloidea, Scolioidea,
Sphecoidea, and Vespoidea in traps using sex
pheromone and synthetic floral volatiles as lures,
however, all traps used white buckets. Because of
the deleterious effect on foraging pollinators and
natural enemies (Meagher & Mitchell 1999), and
the increased time required to service traps con-
taining these insects (Gross & Carpenter 1991),
an additional objective of this study was to collect
and identify nontarget aculeate Hymenoptera at-
tracted to different trap colors.

MATERIALS AND METHODS
1998

Peanuts (Arachis hypogaea L.,'Georgia Green')
were planted during summer in northwestern
Alachua County, Florida. This experiment was
designed to compare moth and aculeate Hy-
menoptera capture in three Universal Moth Trap
(Unitrap) (Great Lakes IPM, Vestaburg, MI) col-
ors (all white, all green, or standard = green can-
opy, yellow funnel, white bucket). Traps were
placed along roads and edges in two fields, and
the experiment was designed as a randomized
complete block with four replications of the three
trap colors. Trap location within a replication was
randomized weekly, and trapping began 21 July
and ended 30 September. Both Trece (Trece,
Inc., Salinas, CA) red septa and Scentry (Eco-
gen, Inc., Langhorne, PA) gray septa S. frugiperda
pheromone lures were used. These lures were al-
ternated and replaced every two weeks. All traps
contained insecticide strips (Hercon Vaportape
II containing 10% dichlorovos, Hercon Environ-
mental Co., Emigsville, PA) to kill captured in-
sects. Trap contents were removed three or more
times per week. Moth numbers per night and Hy-
menoptera numbers per day were compared
across trap colors using a split-block analysis of
variance (ANOVA) (Steel & Torrie 1980). To sat-
isfy ANOVA assumptions, counts were log (x + 1)
transformed before analysis. Means for each trap
color were separated using a LSD mean separa-
tion test (SAS Institute 1996). Untransformed
means (SE) are given in text and figures, whereas
statistical results refer to transformed data.

1999

Four different trapping treatments were
placed at the University of Florida, Hastings Re-
search and Education Center's Yelvington Farm,
St. John's County during July and August. The
four trap colors were standard, white, and stan-
dard traps with buckets spray painted Fluores-
cent Yellow (Painter's Touch #1942, Rust-Oleum
Corp., Vernon Hills, IL) or Sun Yellow Gloss
(Painter's Touch #1945). Traps were placed along


roads among large plots of silage corn (Zea mays
L.). The experiment was designed as a random-
ized complete block with four replications of the
four trap colors. Trap location within a replication
was randomized weekly, and trapping began 13
July and ended 19 August. Scenturion (Scentu-
rion Inc., Clinton, WA) gray septa Fall Armyworm
pheromone lures were used, and were replaced
every two weeks. All traps contained Vaportape II
insecticide strips to kill moths that were cap-
tured. Trap contents were removed three or more
times per week. Moth numbers per night and
Hymenoptera numbers per day were compared
across trap colors using a split-block ANOVA with
log (x + 1)-transformed data. Means for each trap
color or each trap color combination were sepa-
rated using a LSD mean separation test or or-
thogonal contrasts (PROC GLM, CONTRAST
statement, SAS Institute 1996).

RESULTS

1998

Adult male Fall Armyworm numbers in the
trap samples were high during July and August,
and gradually decreased during September (Fig.
1). Comparison of moth captures among three
trap colors showed that the standard traps cap-
tured significantly larger numbers of moths in 20
of 37 sampling dates. Most of the sampling dates
where standard traps captured larger numbers of
moths were during July and August, when traps
were collecting over 50 moths per night. Only
three sampling dates in September produced sig-
nificant differences among traps. The overall av-
erage showed that standard traps captured more
moths than white traps; green traps caught the
fewest number of moths (54.0 4.0, 24.1 + 1.8,
11.9 1.2 moths per night, respectively) (F = 51.2;
df = 2, 6; P = 0.0002).
Collection of nontarget bees and wasps, both in
number of individuals and number of species, was
lower than previously documented (Fig. 2)
(Meagher and Mitchell 1999). Species collected
included Melissodes sp., Apis mellifera (L.), Born-
bus pennsylvanicus (De Geer), Campsomeris plu-
mipes fossulana (F.), Cerceris bicornuta Guerin,
Ammophila spp., and Polistes spp. More Sphe-
coidea were collected in white traps than stan-
dard or green traps (F = 7.3; df = 2, 6;P = 0.0249);
more Vespoidea were collected in standard traps
(F = 4.1; df = 2, 6; P = 0.0743) (Fig. 3). There was
a trend toward fewer Apoidea in green traps.

1999

Consistently large numbers of Fall Armyworm
males were collected in July and August from the
surrounding corn fields (Fig. 3). There were no
differences in number of males per night collected


March 2001





Meagher: Effect of Trap Color In FAW Capture


175

150

125

100

75

50


25 L A A & .*x- .- I4 *It 4
0
M O M N 0 r^ U\ C 00 r tf =
ra r 0 0 r^ ci

Date
Fig. 1. Capture of male Fall Armyworm in standard (green canopy, yellow funnel, white bucket), all-white, or all-
green Unitraps baited with sex pheromone lures, Alachua, FL, 1998.


0.21

0.18


0.15

0.12


0.09

0.06

0.03

0.00


Apoidea


Sphecoidea

I- Vespoidea


Scolioidea


b


B


White


Green


Standard


Fig. 2. Number of aculeate Hymenoptera captured per day in Fall Armyworm pheromone lure bucket traps in
peanut, Alachua, FL, 1998. Means within Sphecoidea followed by the same uppercase letter and Vespoidea followed
by the same lowercase letter, are not significantly different.


z;;.' B






Florida Entomologist 84(1)


100

90

80

70

60

50

40

30

20

10

0


Date
Fig. 3. Capture of male Fall Armyworm in standard (green canopy, yellow funnel, white bucket), fluorescent
(green canopy, yellow funnel, fluorescent yellow bucket), sun yellow (green canopy, yellow funnel, sun yellow
bucket), or all-white Unitraps baited with sex pheromone lures, Hastings, FL, 1999.


in traps with different colors when analyzed
across dates (fluorescent yellow 40.4 4.2, sun
yellow 39.5 4.6, standard 36.7 + 4.7, white 29.0
+ 3.3; F = 2.7; df = 3, 9;P = 0.1089). When each of
the 12 dates was analyzed separately, only 2 dates
(20 July, 2 August) had differences in males cap-
tured among all trap colors (P < 0.05). However,
when different trap color combinations were sub-
jected to contrasts, differences in capture were
noted. Generally, traps with yellow buckets (fluo-
rescent yellow and sun yellow traps) captured


more moths than traps with white buckets (stan-
dard and white traps), and all-white traps col-
lected fewer moths (Table 1).
Very few Vespoidea, Sphecoidea, Tiphioidea,
and Scolioidea were collected. Since more Bom-
bus spp. were collected, their numbers were ana-
lyzed separately from other species of Apoidea.
More Apoidea were collected from white traps
than the other traps, whereas there were no dif-
ferences among trap colors in collection of Bom-
bus spp. (Fig. 4).


TABLE 1. CONTRAST OF NUMBERS OF FALL ARMYWORM MALES CAPTURED BETWEEN TRAPS WITH DIFFERENT COLORED
BUCKETS, HASTINGS, FL, 1999

Contrast F-value Pr > F N Means + SE
fluorescent + sun 7.4 0.0238 96 39.9+ 3.1
vs. white 48 29.0 + 3.3
fluorescent + sun 2.7 0.1350 96 39.9+ 3.1
vs. standard 48 36.7 + 4.7
fluorescent + sun 7.1 0.0257 96 39.9+ 3.1
vs. standard + white 96 32.9 + 2.9
fluorescent + sun + standard 5.3 0.0470 144 38.9 + 2.6
vs. white 48 29.0 + 3.3


A Standard

E-- Fluorescent

-+- Sun Yellow

-- White


I I


March 2001







Meagher: Effect of Trap Color In FAW Capture


0.18


0.15


S0.12


S0.09


0.06


0.03


0.00


* Apoidea


Bombus


Standard Fluorescent Sun Yellow


Fig. 4. Number of Apoidea and Bombus spp. captured per day in Fall Armyworm pheromone lure Unitraps in
corn, Hastings, FL, 1999. Means within Apoidea followed by the same letter are not significantly different.


DISCUSSION

Trap color was shown to influence Fall Army-
worm capture in previous trials (Mitchell et al.
1989; Pair et al. 1989), however in those studies
all-white traps and traps with yellow funnel and
buckets were not compared. My results showed
that more moths were collected in standard traps
than all-white or all-green traps, a result similar
to what has been documented with S. exigua
(Hiibner) (Lopez 1998). Spectral analysis of the
white, yellow, and green components of bucket
traps indicates a possible factor responsible for
decreased capture of moths in green traps was
low light reflectance at wavelengths where moth
eyes are most sensitive (Mitchell et al. 1989).
However, too much reflectance may decrease moth
capture since all-white traps captured fewer
moths than standard traps.
Traps composed of yellow funnels and buckets
tended to collect more males than traps with
white buckets, but differences were not signifi-
cant on all dates. Spectral analysis showed higher
reflectance for fluorescent yellow than sun yellow
in the 500-560 nm range (unpublished data), al-
though this difference appears not to have influ-
enced trap capture. Therefore, if the objective of
monitoring for Fall Armyworm is to collect the
largest number of moths, than it can be concluded


from this research and from previous research
(Meagher & Mitchell 2001), that the standard
Unitrap with green canopy, yellow funnel, and
white bucket is the best collector of male Fall
Armyworm when used with available commercial
sex pheromones.
The attraction of Bombus spp. to traps using
noctuid sex pheromone lures has been previously
documented (Adams et al. 1989; Hendrix & Show-
ers 1990; Gross & Carpenter 1991; Meagher &
Mitchell 1999). Trap color seems to be important
in the capture of bumblebees (Hamilton et al.
1971), although chemical cues either from the
pheromone, the insecticidal strips, or both, may
contribute to capture of these insects (Gross &
Carpenter 1991). As far as capture of other ac-
uleate Hymenoptera (Sphecoidea, Vespoidea, and
Scolioidea) in different colored traps, very little
has been documented.

ACKNOWLEDGMENTS

Technical support in the field was provided by J.
Brady and C. Dillard. Thanks to Rust-Oleum Corp. and
Mark Gorog, Director, Quality and Customer Service,
for providing information about their paints. N. D.
Epsky (USDA-ARS), D. Johanowicz (University of Flor-
ida), and D. Riley (University of Georgia) provided help-
ful reviews of an earlier manuscript.


White











REFERENCES CITED

ADAMS, R. G., K. D. MURRAY, AND L. M. LOS. 1989. Ef-
fectiveness and selectivity of sex pheromone lures
and traps for monitoring fall armyworm (Lepi-
doptera: Noctuidae) adults in Connecticut sweet
corn. J. Econ. Entomol. 82: 285-290.
EPSKY, N. D., R. R. HEATH, A. GUZMAN, AND W. L.
MEYER 1995. Visual cue and chemical cue interac-
tions in a dry trap with food-based synthetic attrac-
tant for Ceratitis capitata and Anastrepha ludens
(Diptera: Tephritidae). Environ. Entomol. 24: 1387-
1395.
GROSS, H. R., AND J. E. CARPENTER. 1991. Role of the
fall armyworm (Lepidoptera: Noctuidae) pheromone
and other factors in the capture of bumblebees (Hy-
menoptera: Apidae) by universal moth traps. Envi-
ron. Entomol. 20: 377-381.
GROSS, H. R., JR., J. E. CARPENTER, AND A. N. SPARKS.
1983. Visual acuity ofHeliothis zea (Lepidoptera: Noc-
tuidae) males as a factor influencing the efficiency of
pheromone traps. Environ. Entomol. 12: 844-847.
HAMILTON, D. W., P. H. SCHWARTZ, B. G. TOWNSHEND,
AND C. W. JESTER. 1971. Effect of color and design of
traps on captures of Japanese beetles and bumble-
bees. J. Econ. Entomol. 64: 430-432.
HENDRICKS, D. E., J. P. HOLLINGWORTH, AND A. W.
HARTSTACK. 1972. Catch of tobacco budworm moths
influenced by color of sexlure traps. Environ. Ento-
mol. 1: 48-51.
HENDRIX, W. H., III, AND W. B. SHOWERS. 1990. Evalu-
ation of differently colored bucket traps for black
cutworm and armyworm (Lepidoptera: Noctuidae).
J. Econ. Entomol. 83: 596-598.
LOPEZ, J. D., JR. 1998. Evaluation of some commercially
available trap designs and sex pheromone lures for


March 2001


Spodoptera exigua (Lepidoptera: Noctuidae). J.
Econ. Entomol. 91: 517-521.
MEAGHER, R. L., JR., AND E. R. MITCHELL. 1999. Non-
target Hymenoptera collected in pheromone- and
synthetic floral volatile-baited traps. Environ. Ento-
mol. 28: 367-371.
MEAGHER, R. L., JR., AND E. R. MITCHELL. 2001. Collec-
tion of fall armyworm (Lepidoptera: Noctuidae) us-
ing selected pheromone lures and trap designs. J.
Entomol. Sci. 36: (in press).
MITCHELL, E. R., H. R. AGEE, AND R. R. HEATH. 1989.
Influence of pheromone trap color and design on cap-
ture of male velvetbean caterpillar and fall army-
worm moths (Lepidoptera: Noctuidae). J. Chem.
Ecol. 15: 1775-1784.
PAIR, S. D., J. R. RAULSTON, A. N. SPARKS, S. R. SIMS,
R. K. SPRENKEL, G. K. DOUCE, AND J. E. CARPENTER
1989. Pheromone traps for monitoring fall army-
worm, Spodoptera frugiperda (Lepidoptera: Noctu-
idae), populations. J. Entomol. Sci. 24: 34-39.
ROBACKER, D. C., D. S. MORENO, AND D. A. WOLFEN-
BARGER. 1990. Effects of trap color, height, and place-
ment around trees on capture of Mexican fruit flies
(Diptera: Tephritidae). J. Econ. Entomol. 83: 412-419.
SAS INSTITUTE. 1996. SAS/STAT guide for personal
computers, version 6.12 ed. SAS Institute, Cary, NC.
SOUTHWOOD, T. R. E. 1978. Ecological methods with
particular reference to the study of insect popula-
tions. Chapman and Hall, London.
STARK, J. D., AND R. I. VARGAS. 1992. Differential re-
sponse of male oriental fruit fly (Diptera: Tephriti-
dae) to colored traps baited with methyleugenol. J.
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McGraw-Hill, NY.


Florida Entomologist 84(1)







Stoetzel & Miller: Aphids on Corn in the U.S.


AERIAL FEEDING APHIDS OF CORN IN THE UNITED STATES
WITH REFERENCE TO THE ROOT-FEEDING APHIS MAIDIRADICIS
(HOMOPTERA: APHIDIDAE)

MANY B. STOETZEL AND GARY L. MILLER
Systematic Entomology Laboratory, Agricultural Research Service
U.S. Department of Agriculture, Beltsville, MD 20705

ABSTRACT

A brief summary of taxonomic characters, usual hosts, and distribution within the United
States are given for each species.Aphis craccivora Koch,Aphis fabae Scopoli,Aphis gossypii
Glover, Aphis maidiradicis Forbes, Hysteroneura setariae (Thomas), Macrosiphum euphor-
biae (Thomas), Metopolophium dirhodium (Walker), Myzus persicae (Sulzer), Rhopalosi-
phum maidis (Fitch), Rhopalosiphum padi (L.), Sipha flava (Forbes), Schizaphis graminum
(Rondani), and Sitobion avenue (Fabricius) are included in the present paper. Pictorial and
dichotomous keys are included to aid personnel charged with detection, identification, and
control of aphids associated with corn in the United States.

Key Words: Taxonomic keys, identification, control, distribution, Zea mays

RESUME

Un breve resume de caracteristicas taxon6micas, hospederos usuales, y distribuci6n dentro
de los Estados Unidos son dados para cada especie.Aphis craccivora Koch,Aphis fabae Sco-
poli,Aphis gossypii Glover,Aphis maidiradicis Forbes, Hysteroneura setariae (Thomas), Ma-
crosiphum euphorbiae (Thomas), Metopolophium dirhodium (Walker), Myzus persicae
(Sulzer), Rhopalosiphum maidis (Fitch), Rhopalosiphum padi (L.), Sipha flava (Forbes),
Schizaphis graminum (Rondani), y Sitobion avenue (Fabricius) son incluidos en este trabajo.
Claves pict6ricas y dicot6micas son incluidas para apoyar al personal encargado de detectar,
identificar, y controlar los afidos asociados con el maiz algod6n en los Estados Unidos.


Corn or maize (Zea mays L.) ranks first among
the agricultural crops in both area devoted to its
cultivation and the value of the annual crop in the
United States. For the 1997 production year, over
80 million acres in the United States were
planted in corn for grain with Iowa the leading
state with over 12 million acres (Anonymous
1999a; Anonymous 1999b). The total value of pro-
duction of corn for grain was over $24 billion in
1997 (Anonymous 1999a). Sweet corn and pop-
corn varieties serve for human consumption
while the field corn varieties are live-stock food,
and the herbage is used for forage. In addition,
corn-based products are used for a wide variety of
items.
In 1996, insecticides were used on 32% of the
total acreage planted for corn (Anonymous
1999c). Over 200 species of insects, several of
which are aphids, have been recorded as injurious
to corn during some part of its life cycle or as a
stored product (Bailey 1935). When aphid colo-
nies are large, they can greatly diminish a plant's
vigor or even kill the plant through mechanical
injury by removal of sap during feeding. Besides
mechanical injury, some aphids are able to trans-
mit diseases that affect corn (Chan et al. 1991).
Aphids also have the capability of transmitting


nonpersistent viruses between plants that would
not otherwise be considered hosts. Aphids also
produce a sticky substance called honeydew dur-
ing feeding. This substance may be problematic
when it fouls the corn tassel and interferes with
pollination and encourages fungal growth.
The aerial aphid fauna includes at least 12
species that commonly colonize corn in the United
States. Several other taxa also feed on the roots of
corn (e.g., Anoecia spp., Geoica spp., Pemphigus
spp.) however, only the most commonly found, the
corn root aphid, Aphis maidiradicis Forbes, will
be addressed in this paper. A brief summary of
taxonomic characters, hosts, worldwide distribu-
tion, and U.S. distribution is given for each of the
13 included species:Aphis craccivora Koch,Aphis
fabae Scopoli, Aphis gossypii Glover, Aphis maid-
iradicis Forbes, Hysteroneura setariae (Thomas),
Macrosiphum euphorbiae (Thomas), Metopoloph-
ium dirhodium (Walker), Myzus persicae (Sulzer),
Rhopalosiphum maidis (Fitch), Rhopalosiphum
padi (L.), Sipha flava (Forbes), Schizaphis grami-
num (Rondani), and Sitobion avenue (Fabricius).
Descriptions as well as written and illustrated
keys are included as an aid for detection, identifi-
cation, and control of aphids associated with corn
in the United States.







Florida Entomologist 84(1)


MATERIALS AND METHODS
In the synonymy section, one asterisk (*) rep-
resents the name used by Palmer (1952) and two
asterisks (**) represent the name appearing in
Blackman & Eastop (1984). Common names are
those approved by the Entomological Society of
America (ESA) (Bosik 1997).
Information on distribution and hosts is taken
from labels on slides in the National Collection of
Insects, Beltsville, Maryland, and from records in
Palmer (1952), Smith & Parron (1978), and Black-
man & Eastop (1984).
In the illustrated keys, the species are grouped
by morphological differences of the antennae and
antennal tubercles, body and antennal setae, pig-
mentation of the abdomen, coloration of cornicle,
size of cauda, number of caudal setae, and wing
venation. Characters used in the keys are appar-
ent with a dissecting microscope with a minimum
power of 16x and are best seen at 50x. Relative
body size of the aphid species follows the division
proposed by Blackman & Eastop (1984): body
length <2.00 mm are "small," 2.00-3.00 mm are
"medium," and >3.00 mm are "large." Figure 1 in-
cludes a figure illustrating general characters of a
wingless and a winged adult. Body length is mea-
sured dorsally from the center of the frons to the
end of the abdomen, excluding the cauda. Length
of the antennal "terminal process" is measured as
the distance from the large primary sensorium to
the tip of the last antennal segment. Length of the
"base" of the antenna is measured from the basal
portion of the last antennal segment to the apex of
the primary sensorium. Caudal length is mea-
sured along the midline from the beginning of the
sclerotized portion to the apex. The keys are not
intended for identification of single, errant aphids
but should be used for individuals fully colonizing
corn. Ideally winged aphids should develop from
nymphs collected from a colony on the plant.

Aphis craccivora Koch 1854
Figs. 1, 4, 6-7
Synonymy:
*Aphis medicaginis Koch 1854
misidentificationn)
**Aphis craccivora Koch
ESA approved common name: cowpea aphid.
Other common names: black legume aphid,
groundnut aphid.
Taxonomic characters: Wingless adult female.-
In life, body shiny black with large black patch on
dorsum of abdomen; legs strikingly white with
black area near apex of femur and tibia; imma-
tures often covered with grayish wax. Small
sized, body length 1.2-1.9 mm, rounded. Antenna
6 segmented; tubercles not well developed; termi-
nal process approximately 12%-21/ times length of
base of antennal segment VI; antennal segments
III-V without secondary sensoria; longest setae


on antennal segment III shorter than diameter of
segment. Cornicle black, cylindrical; approxi-
mately 31/-43/4 times as long as wide, longer than
length of cauda. Cauda black, with 2-4 (usually 3)
pairs of lateral setae and 0-1 dorsal preapical seta.
Winged adult female.-In life body shiny black
with black lateral areas and variable bands on
dorsum of abdomen, legs similar to wingless adult
female; forewing with media twice branched, hind
wing with 2 oblique veins; small to medium sized,
body length 1.4-2.0 mm. Antenna 6 segmented;
tubercles not developed; terminal process approx-
imately 2 times length of base of antennal seg-
ment VI; antennal segment III with 5-7 secondary
sensoria, 1 or 2 noticeably larger than the others,
longest setae on antennal segment III shorter
than diameter of segment; antennal segments IV-
V without secondary sensoria. Cornicle black, cy-
lindrical; 4-5 times as long as wide, longer than
length of cauda. Cauda black, with 2-3 pairs of
lateral setae and 0-1 dorsal preapical seta.
Hosts: Polyphagous with a preference for the
Leguminosae.
Distribution in the United States: Throughout
the United States.
Distribution in the world: Virtually worldwide.
Comments: Aphis craccivora transmits 51
plant viruses but is not listed as a vector of a corn
virus (Chan et al. 1991).

Aphis fabae Scopoli 1763
Figs. 1, 4-7
Synonymy:
& **Aphis fabae Scopoli
ESA approved common name: bean aphid.
Other common name: black bean aphid.
Taxonomic characters: Wingless adult female.-
In life body black, but may appear dull black due to
waxy covering; immatures often covered with wax.
Small to medium sized, body length 1.1-2.5 mm,
rounded. Antenna 6 segmented; tubercles not well
developed; terminal process approximately 2%-32%
times length of base of antennal segment VI; an-
tennal segments III-IV without secondary senso-
ria; longest setae on antennal segment III longer
than diameter of segment. Cornicle dark, cylindri-
cal; 2-4 times as long as wide, longer than length
of cauda. Cauda dark, elongate with 4-7 pairs of
lateral setae and 0-1 dorsolateral setae.
Winged adult female.-In life body dull black,
usually with dark lateral areas and bands on
dorsum of abdomen; forewing with media twice
branched, hind wing with 2 oblique veins; small to
medium sized, body length 1.7-2.2 mm. Antenna 6
segmented; tubercles not well developed; terminal
process approximately 2/3-4 times length of base
of antennal segment VI; 9-20 secondary sensoria
on antennal segment III; 0-6 secondary sensoria
on antennal segment IV; longest setae on anten-
nal segment III longer than diameter of segment.


March 2001







Stoetzel & Miller: Aphids on Corn in the U.S.


I
antenna 5 segmented
cauda knobbed bodyIII IV V




cauda knobbed body setae stout, spinelike


terminal process

base




media twice branched


oblique veins





cornicle




antenna 6 segmented
I II III IV V VI


Sipha flava (Forbes)
yellow sugarcane aphid


body setae fine



%


antennal tubercles well developed


antennal tubercles not well developed


Macrosiphum euphorbiae (Thomas)
Metopolophium dirhodum (Walker)
Myzus persicae (Sulzer)
Sitobion avenae (Fabricius)


wingless adult females
see Fig. 2


winged adult females
see Fig. 3


Aphis craccivora Koch
Aphis gossypil G lover
Hysteroneura setariae (Thomas)
Rhopalosiphum padi (L.)
wingless adult females
see Figs. 4-5


Aphis fabae Scopoli
Aphis maidiradicis Forbes
Rhopalosiphum maidis (Fitch)
Schizaphis graminum (Rondani)
winged adult females
see Figs. 6-7


Fig. 1. Pictorial key to 13 aphid species that commonly colonize corn in the United States.


Cornicle dark, cylindrical; approximately 212-4
times as long as wide, longer than length of cauda.
Cauda dark, elongate with 5-8 pairs of lateral
setae and 0-2 dorsolateral setae.
Hosts: Polyphagous and damaging to many
plants of economic importance.


U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Aphis fabae transmits 42 plant vi-
ruses but is not listed as a vector of a virus of corn
(Chan et al. 1991). Several subspecies have been
described in the A. fabae complex.


7A







Florida Entomologist 84(1)


Aphis gossypii Glover 1877
Figs. 1, 4-7
Synonymy:
& **Aphis gossypii Glover
ESA approved common name: cotton or melon
aphid.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life, body color varying from dark green to pale
yellow or nearly white. Small sized, body length
1.0-1.4 mm, body rounded. Antenna 5-6 seg-
mented; tubercles not well developed, terminal
process approximately 214-3 times length of base
of antennal segment VI; antennal segment III
without secondary sensoria; longest setae on an-
tennal segment III shorter than diameter of seg-
ment. Cornicle dark, cylindrical with slight
tapering; approximately 21/3-5 times as long as
wide, longer than length of cauda. Cauda pale to
dusky, with 2-3 pairs of lateral setae.
Winged adult female.-In life, body shape and
coloration similar to wingless adult female; fore-
wing with media twice branched, hind wing with
2 oblique veins; small sized, body length 1.2-1.8
mm, rounded. Antenna 6 segmented; tubercles
not well developed; terminal process approxi-
mately 23/4-31/ times length of base of antennal
segment VI; antennal segment III with 3-8 sec-
ondary sensoria in a row, longest setae on anten-
nal segment III shorter than diameter of segment;
antennal segments IV-V without secondary senso-
ria. Cornicle dark, cylindrical with slight taper-
ing; approximately 21-3% times as long as wide,
longer than length of cauda. Cauda pale to dusky,
elongate with 2-3 pairs of lateral setae.
Hosts: Polyphagous and very damaging to
many plants of economic importance.
U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Aphis gossypii transmits 76 plant
viruses including sugarcane mosaic virus which
is listed as a virus of corn (Chan et al. 1991).

Aphis maidiradicis Forbes 1891
Figs. 1, 4, 6
Synonymy:
*Aphis maidi-radicis Forbes
**Aphis maidiradicis Forbes
ESA approved common name: corn root aphid.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life body bluish green with dark head and
dusky transverse thoracic and abdominal bands.
Small to medium sized, body length 1.5-2.0 mm
long, body rounded. Antenna 6 segmented; tuber-
cles not well developed, terminal process approx-
imately 11/2-2 times length of base of antennal
segment VI; antennal segment III without sec-
ondary sensoria; longest setae on antennal seg-
ment III shorter than diameter of segment.


Cornicle dusky, cylindrical; approximately 11/2-21/2
times as long as wide, subequal to length of
cauda. Cauda dusky, with 7-8 pairs of lateral se-
tae and 1-2 preapical setae.
Winged adult female.-In life head and thorax
black, abdomen light green with dusky markings;
forewing with media twice branched, hind wing
with 2 oblique veins; body length 1.4-1.9 mm
body, rounded. Antenna 6 segmented; tubercles
not well developed; terminal process approxi-
mately 123-21 times length of base of antennal
segment VI, antennal segment III with 4-11 sec-
ondary sensoria, longest setae on antennal seg-
ment III shorter than diameter of segment;
antennal segment IV with 0-2 secondary senso-
ria, antennal segment IV without secondary sen-
soria. Cornicle dusky, cylindrical; 2-3 times as
long as wide, subequal to length of cauda. Cauda
dusky, with 5-8 pairs of lateral setae and 1-2
preapical setae.
Hosts: Aphis maidiradicis is principally
known as a pest of corn in the U.S. but has been
collected on the roots of a wide range of hosts
(Blackman & Eastop 1984).
Distribution in the United States: Widespread.
Distribution in the world: Brazil, Jamaica,
U.S.A.
Comments:Aphis maidiradicis is not recorded
as transmitting plant viruses (Chan et al. 1991).
This species is found on roots and is often tended
by ants. The taxonomic status ofA. maidiradicis,
A. middletonii, A. armoraciae, and others are un-
clear and require detailed taxonomic and biologi-
cal research.
Hysteroneura setariae (Thomas 1878)
Figs. 1, 4-6
Synonymy:
Siphonophora setariae Thomas
*Aphis setariae (Thomas)
**Hysteroneura setariae (Thomas)
ESA approved common name: rusty plum
aphid.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life body dark reddish brown, apical area of tib-
iae dark, cornicles dark to almost black, cauda pale
to nearly white. Small to medium sized, 1.2-2.2
mm, body rounded. Antenna 6 segmented; tuber-
cles not well developed, terminal process approxi-
mately 41/3-5% times length of base of antennal
segment VI; antennal segments III-V without sec-
ondary sensoria; longest setae on antennal seg-
ment III shorter than diameter of segment.
Cornicle dark to nearly black, tapered apically; ap-
proximately 31/2-41/3 times as long as wide, longer
than length of cauda. Cauda pale to nearly white,
elongate, with 2-3 (usually 2) pairs of lateral setae.
Winged adult female.-In life coloration simi-
lar to wingless adult female; forewing with media
twice branched, hind wing with one oblique vein;


March 2001







Stoetzel & Miller: Aphids on Corn in the U.S.


small sized, body length 1.2-1.8 mm. Antenna 6
segmented; tubercles not well developed, termi-
nal process approximately 6-71/2 times length of
base of antennal segment VI; antennal segment
III with 12-17 secondary sensoria, longest setae
on antennal segment III shorter than diameter of
segment; antennal segment IV with 0-6 second-
ary sensoria; antennal segment V without second-
ary sensoria. Cornicle dark to nearly black,
tapered apically, approximately 41/2-61/2 times as
long as wide, longer than length of cauda. Cauda
pale to nearly white, with 2 pairs of lateral setae.
Hosts: Primary hosts include Prunus spp.
(Blackman & Eastop 1984) however, secondary
hosts include numerous species of Gramineae in-
cluding corn.
U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Hysteroneura setariae transmits
six plant viruses including guinea grass mosaic
virus and sugarcane mosaic virus which are listed
as viruses affecting corn (Chan et al. 1991).

Macrosiphum euphorbiae (Thomas 1878)
Figs. 1-3

Synonymy:
Siphonophora euphorbiae Thomas
*Macrosiphum solanifolii (Ashmead 1882)
**Macrosiphum euphorbiae (Thomas)
ESA approved common name: potato aphid.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life, body color varies between shades of green
or pink. Medium to large sized, body length 2.2-
3.3 mm, pear shaped. Antenna 6 segmented; tu-
bercles well developed with inner faces divergent;
terminal process approximately 4/3-6 times
length of base of antennal segment VI; antennal
segment III with 1-6 secondary sensoria, longest
setae on antennal segment III shorter than diam-
eter of segment; antennal segments IV-V without
secondary sensoria. Cornicle pale or becoming in-
creasingly dusky towards apex, approximately
61/2-9 times as long as wide, longer than length of
cauda, with slight apical constriction and several
rows of polygonal reticulations in constricted
area. Cauda pale, with 3-4 pairs of lateral setae
and 1-3 dorsal preapical setae.
Winged adult female.-In life, body usually of
varying shades of green or pink; forewing with me-
dia twice branched, hind wing with 2 oblique
veins; medium to large sized, body length 2.2-3.0
mm, pear shaped. Antenna 6 segmented; frontal
tubercles well developed with inner faces diver-
gent; terminal process approximately 51-7 times
length of base of antennal segment VI; antennal
segment III with 11-20 secondary sensoria, longest
setae on antennal segment III shorter than diam-
eter of segment; antennal segments IV-V without
secondary sensoria. Cornicle sometimes pale but


usually progressively darker towards apex, with
slight apical constriction and several rows of polyg-
onal reticulations in constricted area, approxi-
mately 713-1013 times as long as wide, longer than
length of cauda. Cauda pale, with 4-5 pairs of lat-
eral setae and 1-2 dorsal preapical setae.
Hosts: Macrosiphum euphorbiae is polypha-
gous and damaging to many plants of economic
importance.
U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Macrosiphum euphorbiae trans-
mits 67 plant viruses but is not listed as vector of
a corn virus (Chan et al. 1991).

Metopolophium dirhodum (Walker 1849)
Figs. 1-3

Synonymy:
Aphis dirhodum Walker
*Macrosiphum dirhodum (Walker)
**Metopolophium dirhodum (Walker)
ESA approved common name: none.
Other common names: rose-grass aphid, rose-
grain aphid.
Taxonomic characters: Wingless adult female.-
In life, body green to yellow green with dark green
longitudinal stripe along the middle of the dor-
sum. Small to medium sized, body length 1.7-2.7
mm, elongate. Antenna 6 segmented with dark
bands on apices of antennal segments III-V, the
base of VI dark near the primary sensoria, and the
terminal process dark; tubercles well developed
with inner faces divergent; terminal process ap-
proximately 3'4-4 times length of base of antennal
segment VI; antennal segment III with 1-2 sec-
ondary sensoria, longest setae on antennal seg-
ment III shorter than diameter of segment;
antennal segments IV-V without secondary senso-
ria. Cornicle pale with darker apices, cylindrical
with slight tapering to apical flange; approxi-
mately 33/4-51/ times as long as wide, longer than
length of cauda. Cauda pale, with 2-4 pair of lat-
eral setae and 2-3 dorsal preapical setae.
Winged adult female.-In life, abdomen green
without markings; forewing with media twice
branched, hind wing with 2 oblique veins; small
to medium sized, body length 1.9-2.6 mm, elon-
gate. Antenna 6 segmented; frontal tubercles well
developed with inner faces divergent; terminal
process approximately 3'4-4 times length of base
of antennal segment VI; antennal segment III
with 14-21 secondary sensoria over most of the
length, longest setae on antennal segment III
shorter than diameter of segment; antennal seg-
ments IV-V without secondary sensoria. Cornicle
pale with darker apices, cylindrical with slight ta-
pering to apical flange, approximately 4-61/2 times
as long as wide, longer than length of cauda.
Cauda pale, with 3-4 pairs of lateral setae and 2-
4 dorsal preapical setae.







Florida Entomologist 84(1)



wingless adult females
antennal tubercles well developed


March 2001


cornicle with apical area of polygonal reticulation




czzi \


cornicle without apical area of polygonal reticulation





.=. I .. 7 .:


cornicle pale, becoming dusky toward apex cornicle black, cylindrical
reticulations in indented area


Macrosiphum euphorbiae (Thomas)
potato aphid


Sitoblon avenue (Fabriclus)
English grain aphid


antennal tubercles divergent


Metopolophium dirhodum (Walker)


antennal tubercles convergent







Myzus persicae (Sulzer)
green peach aphid


Fig. 2. Pictorial key to wingless adult females of four aphid species that commonly colonize corn in the United
States and have well developed antennal tubercles.


Hosts: Primary hosts of M. dirhodum include
wild and cultivated species of Rosa, however,
secondary hosts include several species of
Gramineae including corn.


U.S. distribution: Widespread except in tropics.
Distribution in the world: Africa, Central Asia,
Europe, the Middle East, New Zealand, North
America, and South America.


I -







Stoetzel & Miller: Aphids on Corn in the U.S.


winged adult females
antenna tubercles well developed


cornicle with apical area of polygonal reticulation


cornicle without apical area of polygonal reticulation


pZ 1==z03


I I it.'i


cornicle pale, becoming dusky toward apex
reticulations in indented area


Macrosiphum euphorbiae (Thomas)
potato aphid


cornicle black, cylindrical



Sitoblon avenae (Fabricius)
English grain aphid


dorsum of abdomen with large dark patch;
cornicles with slight apical swelling and medial constriction









Myzus persicae (Sulzer)
green peach aphid


I
abdomen without dorsal patch;
cornicles cylindrical without constriction










Metopolophium dirhodum (Walker)


Fig. 3. Pictorial key to winged adult females of four aphid species that commonly colonize corn in the United
States and have well developed antennal tubercles.


Comments: Metopolophium dirhodum trans- dwarf virus which is listed as a virus affecting
mits three plant viruses including barley yellow corn (Chan et al. 1991).


A. -





aug


. M_-._ ---







Florida Entomologist 84(1)



wingless adult females
antenna tubercles not well developed


I
cornicle length subequal to caudal length





Aphis maidiradicis Forbes
corn root aphid


abdomen with large dark dorsal patch


March 2001


ornice longer than cada
cornice longer than cauda


abdomen either banded or without large dorsal patch
AA


Aphis craccivora Koch
cowpea aphid


cauda pale and cornicle pale






Schizaphis graminum (Rondani)
greenbug


cornicle dark or black and cauda pale, dusky or dark


Aphis fabae Scopoli
Aphis gossypli Glover
Hysteroneura setariae (Thomas)
Rhopalostphum maidis (Fitch)
Rhopalosiphum padi (L.)
continued on Fig. 5


Fig. 4. Pictorial key to wingless adult females of eight aphid species that commonly colonize corn in the United
States and have antennal tubercles not developed.


8-S







Stoetzel & Miller: Aphids on Corn in the U.S.


Myzus persicae (Sulzer 1776)
Figs. 1-3

Synonymy:
Aphis persicae Sulzer
& .L :... persicae (Sulzer)
ESA approved common name: green peach
aphid.
Other common name: peach-potato aphid.
Taxonomic characters: Wingless adult female.-
In life, body color varies from green to pale yellow.
Small to medium sized, body length 1.5-2.1 mm,
pear shaped. Antenna 6 segmented; tubercles
well developed with inner faces convergent; ter-
minal process approximately 314 -41/2 times length
of base of antennal segment VI; antennal seg-
ments III-V without secondary sensoria, longest
setae on antennal segment III shorter than diam-
eter of III. Cornicle pale but apex may be dark,
slight apical swelling and slight medial constric-
tion; approximately 4%-73/4 times as long as wide,
longer than length of cauda. Cauda pale to dusky,
with 3 pairs of lateral setae.
Winged adult female.-In life, body varies from
green to pale yellow with a large dark patch on
dorsum of abdomen; forewing with media twice
branched, hind wing with 2 oblique veins; small to
medium sized, body length 1.4-2.2 mm, pear
shaped. Antenna 6 segmented; tubercles well de-
veloped with inner faces convergent; terminal
process approximately 23-4%/ times length of base
of antennal segment VI; antennal segment III
with 6-16 secondary sensoria, longest setae on an-
tennal segment III shorter than diameter of seg-
ment; antennal segments IV-V without secondary
sensoria. Cornicle dusky to dark but apex some-
times darker, slight apical swelling and slight me-
dial constriction; approximately 4/3-9 times as
long as wide, longer than length of cauda. Cauda
pale to dusky, with 3 pairs of lateral setae.
Hosts: Primary hosts include several species of
Prunus, however M. persicae is polyphagous and
damaging to many other plants of economic im-
portance.
U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Myzus persicae transmits more
than 182 plant viruses including barley yellow
dwarf virus and sugarcane mosaic virus which are
listed as viruses affecting corn (Chan et al. 1991).

Rhopalosiphum maidis (Fitch 1856)
Figs. 1, 4-7

Synonymy:
Aphis maidis Fitch
& **Rhopalosiphum maidis (Fitch)
ESA approved common name: corn leaf aphid.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life, body color blue green to olive green with


reddish-purple areas around cornicle bases, occa-
sionally wax covered. Small sized, body length
1.7-2.6 mm, pair shaped. Antenna 6 segmented;
tubercles not well developed, terminal process ap-
proximately 2-21/3 times length of base antennal
segment VI; antennal segments III-V without sec-
ondary sensoria, longest setae on antennal seg-
ment III longer than diameter of segment.
Cornicle dark, slightly constricted apically, 21/2-
31/ times as long as wide, longer than length of
cauda. Cauda dark, with 2 pairs of lateral setae.
Winged adult female.-In life, abdominal color
yellow green to dark green; forewing with media
twice branched; hind wing with 2 oblique veins;
small sized, body length 1.6-2.0 mm. Antenna 6
segmented, terminal process approximately 12 -
213 times length of base antennal segment VI; an-
tennal segment III with 11-20 secondary senso-
ria, longest setae on antennal segment III shorter
than diameter of segment; antennal segment IV
with 1-6 secondary sensoria; antennal segment V
with 0-4 secondary sensoria. Cornicle dark,
slightly constricted apically, 21/2-31/2 times as long
as wide, longer than length of cauda. Cauda dark,
with 2 pairs of lateral setae.
Hosts: Rhopalosiphum maidis feeds on numer-
ous species of Gramineae including many that are
economically important.
U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Rhopalosiphum maidis transmits
more than 15 plant viruses, including barley yel-
low dwarf virus, guinea grass mosaic virus, and
sugarcane mosaic virus which are listed as affect-
ing corn (Chan et al. 1991).
Rhopalosiphum padi (Linnaeus 1758)
Figs. 1, 4-7
Synonymy:
Aphis padi Linnaeus
& **Rhopalosiphum padi (Linnaeus)
ESA approved common name: bird cherry-oat
aphid.
Other common names: oat bird-cherry aphid.
Taxonomic characters: Wingless adult female.-
In life, body color varies from light yellow green
mottling to dark green, often with orange patches
around base of cornicles. Small to medium sized,
body length 1.5-2.1 mm, pear shaped. Antenna 6
segmented; tubercles not well developed, termi-
nal process approximately 4-51/2 times length of
base antennal segment VI; antennal segments
III-V without secondary sensoria, longest setae
on antennal segment III shorter than diameter of
segment. Cornicle dark, cylindrical, slightly con-
stricted apically; approximately 2/3-4 times as
long as wide, longer than length of cauda. Cauda
dark, with 2-3 (usually 2) pairs of lateral setae.
Winged adult female.-In life, abdominal color
light green to dark green; forewing with media
twice branched, hind wing with 2 oblique veins;







Florida Entomologist 84(1)


March 2001


continued from Fig. 4

cornicle dark or black and cauda pale, dusky or dark


abdomen with dorsal dark bands;
cauda with 4-7 pairs of lateral setae


I
abdomen without dorsal dark bands;
cauda with 3 or fewer pairs of lateral setae
J .


Aphis fabae Scopoli
bean aphid



cauda pale or dusky
_______\_______I


apex of femur dark or black




Hysteroneura setariae (Thomas)
rusty plum aphid


apex of femur without dark or black coloration


Aphis gossypii Glover
cotton or melon aphid


terminal process >3 times length of base;
antennal setae shorter than width of segment




Rhopalosiphum padi (L.)
bird cherry-oat aphid


terminal process < 3 times length of base;
antennal setae longer than width of segment




Rhopalosiphum maidis (Fitch)
corn leaf aphid


Fig. 5. Continued pictorial key to wingless adult females of eight aphid species that commonly colonize corn in
the United States and have antennal tubercles not developed.


small to medium sized, body length 1.6-2.0 mm. An- ria, longest setae on antennal segment III shorter
tenna 6 segmented, terminal process approximately than diameter of segment; antennal segment IV
41/3-51/3 times length of base antennal segment VI; with 3-9 secondary sensoria; antennal segment V
antennal segment III with 11-21 secondary senso- with 0-1 secondary sensoria. Cornicle dark, cylin-


cauda dark or black










Stoetzel & Miller: Aphids on Corn in the U.S.


winged adult females
antennal tubercles not well developed


forewing with media once branched


forewing with media twice branched


Schizaphis graminum (Rondani)
greenbug


hind wing with one oblique vein


hind wing with two oblique veins


Hysteroneura setariae (Thomas)
rusty plum aphid


cornicle length subequal to caudal length






Aphis maidiradicis Forbes
corn root aphid


cornicle longer than cauda


Aphis craccivora Koch
Aphis fabae Scopoli
Aphis gossypii Glover
Rhopalosiphum maidis (Fitch)
Rhopalosiphum pad! (L.)
continued on Fig. 7


Fig. 6. Pictorial key to winged adult females of eight aphid species that commonly colonize corn in the United
States and have antennal tubercles not developed.







Florida Entomologist 84(1)


continued from Fig. 6

cornicle longer than cauda


antennal segment III with 5-7 secondary sensoria,
one noticeably larger than other



Aphis craccivora Koch
cowpea aphid


antenna segment III with secondary sensoria
all subequal in size
or
with numerous secondary sensoria of various sizes


cauda with 2-3 pairs of setae

", ijt


antenna segment III with 3-8 secondary sensoria




Aphis gossypii Glover
cotton or melon aphid


terminal process >4 times the base
terminal process >4 times the base


Rhopalosiphum padi (L.)
bird cherry-oat aphid


I
antenna segment III with >10 secondary sensoria

4. -r^--


terminal process < 4 times the base


Rhopalosiphum maidis (Filch)
corn leaf aphid


Fig. 7. Continued pictorial key to winged adult females of eight aphid species that commonly colonize corn in the
United States and have antennal tubercles not developed.


drical, slightly constricted apically; approximately Hosts: Primary host of R. padi in North Amer-
4-62% times as long as wide, longer than length of ica is Prunus virginiana, however it also feeds on
cauda. Cauda dark, with 2 pairs of lateral setae. numerous species of Gramineae including corn.


cauda with 5-8 pairs of setae


Aphis fabae Scopoli
bean aphid


March 2001







Stoetzel & Miller: Aphids on Corn in the U.S.


U.S. distribution: Widespread.
Distribution in the world: Virtually worldwide.
Comments: Rhopalosiphum padi transmits
more than 15 plant viruses, including barley yel-
low dwarf virus, maize leaf fleck virus, and sugar-
cane mosaic virus which are listed as affecting
corn (Chan et al. 1991).

Schizaphis graminum (Rondani 1852)
Figs. 1, 4, 6
Synonymy:
Aphis graminum Rondani
*Toxoptera graminum (Rondani)
**Schizaphis graminum (Rondani)
ESA approved common name: greenbug.
Other common names: none.
Taxonomic characters: Wingless adult female.-
In life, body green to yellow green, dorsum often
with median longitudinal stripe. Small to medium
sized, body length 1.6-2.2 mm, elongate; body setae
fine, inconspicuous. Antenna 6 segmented; tuber-
cles not well developed; terminal process approxi-
mately 33-43/4 times length of base of antennal
segment VI; antennal segments III-V without sec-
ondary sensoria; longest setae on antennal segment
III shorter than diameter of segment. Cornicle pale,
sometimes apically dusky, approximately 4 -'- .
times as long as wide, longer than length of cauda.
Cauda pale with 2-3 pairs of lateral setae.
Winged adult female.-In life, head and pro-
thorax yellow brown, abdomen green to yellow
green; forewing with media once branched, hind
wing with 2 oblique veins; small to medium sized,
body length 2.6-3.0 mm, body setae fine, incon-
spicuous. Antenna 6 segmented; tubercles not
well developed; terminal process approximately
3%-4% times length of base of antennal segment
VI; antennal segment III with 5-9 secondary sen-
soria, longest setae on antennal segment III
shorter than diameter of segment; antennal seg-
ments IV-V without secondary sensoria. Cornicle
pale, sometimes apically dusky, approximately
31/2-5 times as long as wide, longer than length of
cauda. Cauda pale, with 2-3 pairs of lateral setae.
Hosts: Hosts are several species of Gramineae.
U.S. distribution: Widespread.
Distribution in the world: Africa, Central Asia,
Central America, Japan, Korea, Middle East, Ne-
pal, North America, Pakistan, South America,
Taiwan, and Thailand.
Comments: Schizaphis graminum transmits 3
plant viruses, including barley yellow dwarf virus
and sugarcane mosaic virus which are listed as
affecting corn (Chan et al. 1991).

Sipha flava (Forbes 1884)
Fig. 1
Synonymy:
Chaitophorus flava Forbes
*Sipha flava (Forbes), in key


**Sipha flava (Forbes)
ESA approved common name: yellow sugar-
cane aphid.
Other common names: yellow sugar cane aphid.
Taxonomic characters: Wingless adult female.-
In life, body yellow to green, often with paired
intersegmental marking on dorsum. Small sized,
body length 1.6-2.1mm, oval shaped, covered with
stout, spinelike setae. Antennae 5 segmented; tu-
bercles not well developed; terminal process ap-
proximately 414-614 times length of base of
antennal segment V; antennal segments III-IV
without secondary sensoria; longest setae on an-
tennal segment II longer than diameter of seg-
ment. Cornicle dusky, stout, approximately half
as long as wide, shorter than length of cauda.
Cauda pale, knobbed, with 3 pairs of lateral setae
and 0-1 preapical setae.
Winged adult female.-In life, abdomen yellow
with variable dorsal dark markings; forewing
with media twice branched, hind wing with 2 ob-
lique veins; small to medium sized, body length
1.5-2.0 mm, covered with stout, spine-like setae.
Antennae 5 segmented; tubercles not well devel-
oped; terminal process approximately 13/4-23/4
times length of base of antennal segment V; an-
tennal segment III with 3-6 secondary sensoria,
longest setae on antennal segment III longer than
diameter of segment; antennal segment IV with-
out secondary sensoria. Cornicle dusky, stout, ap-
proximately half as long as wide, shorter than
length of cauda. Cauda pale, knobbed, with 3-4
pairs of lateral setae and 0-1 preapical setae.
Hosts: Hosts are several species of Gramineae.
U.S. distribution: Widespread.
Distribution in the world: Caribbean, Central
America, North America, South America.
Comments: Sipha flava transmits sugarcane
mosaic virus which is listed as affecting corn
(Chan et al. 1991).

Sitobion avenue (Fabricius 1775)
Figs. 1-3

Synonymy:
Aphis avenue Fabricius
*Macrosiphum granarium (Kirby 1798)
**Sitobion avenue (Fabricius)
ESA approved common name: English grain
aphid.
Other common names: grain aphid.
Taxonomic characters: Wingless adult female.-
In life, body yellow green to red brown, dorsum of-
ten with faint intersegmental markings. Small to
medium sized, body length 2.2-3.8 mm, elongate;
body setae fine, inconspicuous. Antenna 6 seg-
mented; tubercles well developed, inner faces di-
vergent; terminal process approximately 41/2-61/2
times length of base of antennal segment VI; an-
tennal segments III-V without secondary senso-
ria; longest setae on antennal segment III shorter







Florida Entomologist 84(1)


than diameter of segment. Cornicle black, cylin-
drical and apically reticulated, approximately
4 -5 times as long as wide, subequal to length of
cauda. Cauda pale, with 2-5 pairs of lateral setae
and 0-1 preapical setae.
Winged adult female.-In life, coloration simi-
lar to wingless adult female but intersegmental
markings are more distinct; forewing with media
twice branched, hind wing with 2 oblique veins;
small to medium sized, body length 1.8-2.8 mm;
body setae fine, inconspicuous. Antenna 6 seg-
mented; tubercles well developed, inner faces di-
vergent; terminal process approximately 513-612
times length of base of antennal segment VI; an-
tennal segment III with 5-13 secondary sensoria,
longest setae on antennal segment III shorter than


diameter of segment; antennal segments IV-V
without secondary sensoria. Cornicle black, cylin-
drical and apically reticulated, approximately
41/2-61/2 times as long as wide, subequal to length
of cauda. Cauda pale, with 3-5 pairs of lateral setae
and 1-2 preapical setae.
Hosts: Several species of Gramineae, including
all major cereals and pasture grasses.
U.S. distribution: Widespread.
Distribution in the world: Africa (in part), Cen-
tral Asia, Central America, India, the Mediter-
ranean, Middle East, Nepal, North America,
Pakistan, and South America
Comments: Sitobion avenue transmits 4 plant
viruses, including barley yellow dwarf virus which
is listed as affecting corn (Chan et al. 1991).


KEY TO THE AERIAL FEEDING WINGLESS ADULT FEMALE APHIDS OF CORN IN THE UNITED STATES

With Reference to the Root-feeding,Aphis maidiradicis Forbes

1. Antenna 5-segmented; body setae stout, spine like; cornicle short, its length approximately
half of its width ........................... yellow sugarcane aphid, Sipha flava (Forbes)
Antenna 6-segmented; body setae fine, inconspicuous; cornicle elongate, its length greater
than half its width .............................................. ............. 2
2(1) Antennal tubercles not well developed, not extending beyond frons or approximately
even w ith frons (Fig. 1) .......................................................... 3
Antennal tubercles well developed, extending beyond frons (Fig. 1) ..................... 10
3(2) Longest setae on antennal segment III longer than the diameter of the segment .......... .4
Longest setae on antennal segment III shorter than the diameter of the segment .......... 5
4(3) Cornicle with apical constriction; cauda with 2 pairs of lateral setae
....................................... corn leaf aphid, Rhopalosiphum maidis (Fitch)
Cornicle cylindrical, without apical constriction; cauda with 4-7 pairs of lateral setae
................................................... bean aphid,Aphis fabae Scopoli
5(3) Cornicle pale, sometimes apically dusky ......... greenbug, Schizaphis graminum (Rondani)
Cornicle dark ................................ ..... ....... ......... ............. 6
6(5) Cornicle length subequal to caudal length ....... corn root aphid,Aphis maidiradicis Forbes
Cornicle longer than cauda ....................................................... 7
7(6) Abdomen with large dark dorsal patch ............... cowpea aphid,Aphis craccivora Koch
Abdomen without large dark dorsal patch, abdomen may have small dorsal marking
or no markings ................... ............................................. 8
8(7) Cornicle cylindrical with apical constriction; cauda dark
............................. bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus)
Cornicle cylindrical or tapered without apical constriction; cauda pale or dusky. ........... 9
9(8) Terminal process >4 times length of base; cauda pale to white
.................................... rusty plum aphid, Hysteroneura setariae (Thomas)
Terminal process < 4 times length of base; cauda dusky to pale
......................................... cotton or melon aphid,Aphis gossypii Glover
10(2) Cornicle with polygonal reticulation .............................................. 11
Cornicle without polygonal reticulation .......................................... .12
11(10) Cornicle black, 5 times as long as wide, subequal to length of cauda
...................................... English grain aphid, Sitobion avenue (Fabricius)
Cornicle sometimes pale or becoming increasing dusky toward apex, 61/2 times as long as wide,
longer than the length of cauda ........... potato aphid, Macrosiphum euphorbiae (Thomas)


March 2001







Stoetzel & Miller: Aphids on Corn in the U.S.


12(10) Antennal tubercles with inner faces convergent; cornicle with slight apical swelling
and slight medial constriction ................. green peach aphid, Myzus persicae (Sulzer)
Antennal tubercle with inner face divergent; cornicle cylindrical with slight tapering
to an apical flange ................... rose-grass aphid, Metopolophium dirhodum (Walker)

KEY TO THE AERIAL FEEDING WINGED ADULT FEMALE APHIDS OF CORN IN THE UNITED STATES

With Reference to the Root-feeding,Aphis maidiradicis Forbes

1. Antenna 5-segmented; body setae stout, spine like; cornicle short, its length approximately
half of its width ........................... yellow sugarcane aphid, Sipha flava (Forbes)
Antenna 6-segmented; body setae fine, inconspicuous; cornicle elongate, its length greater
than half its width .............................................. ............. 2
2(1). Antennal tubercles not well developed, not extending beyond frons or approximately
even w ith frons (Fig. 1) .......................................................... 3
Antennal tubercles well developed, extending beyond frons (Fig. 1) ..................... 10
3(2) Hind wing with one oblique vein; terminal process 6 times the length of the base
of antennal segment VI. ................ rusty plum aphid, Hysteroneura setariae (Thomas)
Hind wing with two oblique veins; terminal process < 6 times the length of the base
of antenna segment VI ........................ .......... ........................ 4
4(3) Forewing with media once branched; cornicle pale sometimes dusky apically
.......................................... greenbug, Schizaphis graminum (Rondani)
Forewing with media twice branched; cornicle black or dusky .......................... 5
5(4) Cornicle length subequal to caudal length ....... corn root aphid,Aphis maidiradicis Forbes
Cornicle longer than cauda ....................................................... 6
6(5) Longest setae on antennal segment III longer than diameter of segment; cauda with 5-8
pairs of lateral setae and 0-2 preapical setae .............. bean aphid,Aphis fabae Scopoli
Longest setae on antennal segment III shorter than diameter of segment; cauda
with <5 pairs of lateral setae ..................................................... 7
7(6) Antennal segment III with < 11 secondary sensoria and antennal segment IV
without secondary sensoria ........................... ......................... 8
Antennal segment III with 11 secondary sensoria and antennal segment IV
with secondary sensoria ......................................................... 9
8(7) Cornicle and cauda black .......................... cowpea aphid,Aphis craccivora Koch
Cornicle dark and cauda pale to dusky ......... cotton or melon aphid,Aphis gossypii Glover
9(7) Terminal process < 3 times the length of the base
.................................. corn leaf aphid, Rhopalosiphum maidis (Fitch)
Terminal process > 4 times the length of the base
............................. bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus)
10(2) Cornicle with polygonal reticulation .............................................. 11
Cornicle without polygonal reticulation .......................................... .12
11(10) Cornicle black, 7 times as long as wide, subequal to length of cauda
...................................... English grain aphid, Sitobion avenue (Fabricius)
Cornicle sometimes pale or becoming increasing dusky toward apex, >7 times as long
as wide, longer than length of cauda ....... potato aphid, Macrosiphum euphorbiae (Thomas)
12(10) Abdomen with large dark dorsal patch; cornicle with slight apical swelling
and slight medial constriction ................. green peach aphid, Myzus persicae (Sulzer)
Abdomen without large dark dorsal patch; cornicle cylindrical with slight tapering
to an apical flange ................... rose-grass aphid, Metopolophium dirhodum (Walker)

ACKNOWLEDGMENTS REFERENCES CITED
We wish to thank Andrew S. Jensen (Moses Lake, ANONYMOUS. 1999a. United States crop rankings-
WA), Michael E. Schauff(USDA-ARS, Washington, DC), 1997 production year. [web page] http://usda2.
and Sonja J. Scheffer (USDA-ARS, Beltsville, MD) for mannlib.cornell.edu/data-sets/crops/9X180/98180/
their helpful comments and suggestions. crpnkus.txt accessed 11 March 1999].












ANONYMOUS. 1999b. State rankings-1997 crop year
based on production. Top ten states and United States.
[web page] http://usda2.mannlib.cornell.edu/datasets/
crops/9X180/98180/2/fieldcrp.txt [accessed 11 March
1999].
ANONYMOUS. 1999c. Agricultural chemical usage-1996
field crops summary. [web page] http://usda.mannlib.
cornell.edu/data-sets/inputs/9X171/97171/agch0997.
txt [accessed 11 March 1999].
ASHMEAD, W. H. 1882. On the Aphididae of Florida, with
descriptions of new species. Canadian Entomol.
14:88-93.
BAILEY, L. H. 1935. The Standard Cyclopedia of Horti-
culture. The Macmillian Co., New York, 3639 pp.
BLACKMAN, R. L., AND V. F. EASTOP. 1984.Aphids on the
world's crops: An identification and information
guide. John Wiley & Sons, Ltd., Chichester, 466 pp.
BOSIK, J. J. (Chair). 1997. Common Names of Insects &
Related Organisms 1997. Entomological Society of
America, Lanham, MD, 238 pp.
CHAN, C. K., A. R. FORBES, AND D. A. RAWORTH. 1991.
Aphid-transmitted viruses and their vectors of the
world. Agric. Canada Res. Branch Tech. Bull. 1991-
3E, 216 pp.
FABRICIUS, J. C. 1775. Rhyngota. System Entomolo-
giae. Sistens insectorum classes, ordines, genera,
species, adiectis synonymis, locis, descriptionibus,
observationibus, Korte 1775: 1-816.
FITCH, A. 1856. Second report on the noxious, beneficial
and other insects, of the State of New York. Trans.
N.Y. State Agric. Soc. 15: 409-559.
FORBES, S. A. 1884. Recent observations. Plant lice-
Aphides. Order Hemiptera. Family Aphididae. Rept.
State Entomol. (Illinois) 13: 41-54.
FORBES, S. A. 1891. A summary history of the corn-root
Aphis. (Aphis maidi-radicis, n. sp.). Rept. State En-
tomol. (Illinois) 17:1-90.


March 2001


GLOVER, T. 1877. Homoptera. In Report of the entomol-
ogist and curator of the museum. Report of the Com-
mission on Agriculture 1876: 17-46.
KIRBY, W. 1798. XX. History of Tipula tritici, and Ich-
neumon tipulae, with some observations upon other
insects that attend the wheat, in a letter to Thomas
Marsham, Esq. Trans. Linnaean Soc. (London) 4:
230-239.
KOCH, C. L. 1854. Die Pfanzenlause Aphiden, gertreu
nach dem Leben abgebildet und beschrieben. Ntrn-
berg Hefts II-IV: 1-134.
LINNAEUS, C. 1758. II. Hemiptera. System Naturae per
regna tria naturae, secudum classes, ordines, general,
species, cum characteribus, differentilis, synonymis,
locis. Editio decima, reformata 1: 1-824 [451-453].
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Region. Thomas Say Foundation 5: 1-452.
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ante in numerosa term sulla citta di Parma. Nuove
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hibens insecta Carnioliae indigena et distribute in
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of Aphididae (Homoptera) of North America. North
Carolina Agric. Exp. Stn. Tech. Bull. 255: 428 pp.
SULZER, J. H. 1776. Die Blattlatse, pp. 98-105. In Ab-
gekirzte Geschichte der Insekten nach dem Linaeis-
chen System. 274 pp.
THOMAS, C. 1878. A list of the species of the tribe Aphi-
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Nat. Hist. 3: 43-53.


Florida Entomologist 84(1)







Brailovsky & Barrera: Six new species of Mozena


SIX NEW SPECIES OF MOZENA FROM MEXICO
(HETEROPTERA: COREIDAE: COREINAE: NEMATOPODINI)

HARRY BRAILOVSKY AND ERNESTO BARRERA
Institute de Biologia, UNAM, Departamento de Zoologia, Apdo Postal 70153, M6xico 04510 D.F. M6xico

ABSTRACT
Six new species of Mozena, M. atra, M. nogueirana, M. pardalota, M. perezae, M. preclara,
and M. presigna, collected in Mexico, are described; dorsal habitus, antennal segments,
pronotum, abdomen in lateral view, paramere and male genital capsule of most of the species
are illustrated.
Key Words: Insecta, Heteroptera, Coreidae, Nematopodini, Mozena, new species, Mexico

RESUME
Seis nuevas species de Mozena, M. atra, M. nogueirana, M. pardalota, M. perezae, M. pre-
clara, y M. presigna, colectadas en M6xico son descritas; el cuerpo en vista dorsal, las ante-
nas, el pronoto, el abdomen en vista lateral, los parameros y la capsula genital del macho de
la mayoria de las species son ilustrados.


The genus Mozena Amyot and Serville (1843)
is a large, complex group that ranges from the
Southern United States, throughout Mexico,
Cuba, and Central America to Northeastern
South America including Colombia and Venezu-
ela, with the greatest number of species being
known from Mexico (Brailovsky 1999).
These are medium-sized to large coreids which
are rather variable in color and size as well as in
the general development of the humeral angles of
the pronotum, development of the hind femur,
and allometry of the scutellum.
Within the tribe Nematopodini,Mozena can be
recognized by the triangular, flat, apically acute
scutellum, the hind tibia only dilated ventrally, the
humeral pronotal angles produced but not into
sharp spines, the body usually longer than 20.00
mm, the tylus produced anterior to antennifers,
the dorsal surface of the hind femur armed with
tubercles or spines in three or more rows, the
outer surface of the male hind coxa with large and
robust tubercle (blunt in female without tubercle),
and the mesosternum with a median sulcus be-
tween the bases of the fore coxae, with in which
the rostrum usually lies. In the related genus Pi-
ezogaster Amyot and Serville the anterior third of
the mesosternum lacks a median longitudinal
sulcus (O'Shea 1980).
The genus is usually associated with Legumino-
sae, and has been collected on Mesquite (Prosopis
spp.), sweet acacia (Acacia spp.), and Schrankia
uncinata (Ward et al. 1977). The biology of most
species is poorly known. Brailovsky et al. (1995)
studied the immature stages, life history, and bio-
logical aspects of Mozena lunata (Burmeister).
Previous to this paper, 15 species and one sub-
species of Mozena were known in Mexico (M. affinis
(Dallas), M. arizonensis Ruckes, M. brunnicornis


(H. S.), M. buenoi Hussey, M. gaumeri Distant, M.
hector Van Duzee, M. lineolata (H.S.), M. lunata
(Burmeister), M. lunata rufescens Ruckes, M. lur-
ida (Dallas), M. lutea (H.S.), M. nestor (Stal), M.
pallisteri Ruckes, M. rufula Van Duzee, M. scrupu-
losa (Stil), and M. ventralis (Mayr). This contribu-
tion adds six new species.
The following abbreviations are used to identify
institutions where types are deposited or which
generously lent material for this paper: AMNH:
American Museum of Natural History, New York;
BMNH: The Natural History Museum, London,
England; BYU: Brigham Young University, Monte
L. Bean Life Science Museum, Provo, UT; CAS:
California Academy of Sciences, San Francisco;
CMN: Carnegie Museum of Natural History, Pitts-
burgh; CUIC: Cornell University, Insect Collec-
tion, Ithaca, NY; FNS: Forschungsinstitut und
Naturmuseum Senckenberg, Germany; FMNH:
Field Museum Natural History, Chicago, IL;
FSCA: Florida State Collection of Arthropods,
Gainesville, FL; LACM: Los Angeles County Mu-
seum, CA; NMW: Naturhistorisches Museum,
Wien; NRE: Naturhistoriska Riksmuseet, Stock-
holm; TAMU: Texas A&M University, College Sta-
tion; UCB: University of California, Berkeley;
UCD: University of California, Davis; UGA: Uni-
versity of Georgia, Athens, GA; UNAM: Instituto
de Biologia, Universidad Nacional Autonoma de
Mexico; USNM: National Museum of Natural His-
tory, Smithsonian Institution, Washington, DC.
All measurements are given in millimeters.

Mozena atra Brailovsky and Barrera, New Species
Figs. 13, 26

Description. Male holotypee). Dorsal colora-
tion: head including antennal segments I to IV or-







Florida Entomologist 84(1)


ange; pronotum bright chestnut orange with
outer margin of humeral angles black, and small
tubercles dark yellow; scutellum creamy yellow,
with chestnut orange spot on basal and middle
third; clavus and corium chestnut orange, with
middle third of costal margin whitish; hemelytral
membrane dark amber-like, with veins darker;
connexival segments III to VII reddish brown,
with anterior third yellow, and posterior border
and spines black; dorsal abdominal segments
light orange yellow. Ventral coloration. Bright or-
ange with following areas yellow: acetabulae, tu-
bercles nearest each acetabulae, posterior margin
of propleura, and anterior third of pleural abdom-
inal sterna III to VII; rostral segments orange
with apex of IV black; propleura, mesopleura, and
metapleura with clearly creamy yellow vittae ob-
liquely directed; anterior and posterior lobe of
metathoracic peritreme black; fore and middle
legs bright orange, with coxae tinged with bright
red; hind leg with coxa and trochanter bright or-
ange red, femur dark orange with ventral spines
black, tibia with inner surface bright black, and
outer surface and distal third bright red to orange
red, tarsus bright orange; creamy yellow vittae
along each side of abdominal sterna broken into
two sections on each sternite, the anterior one
small and more or less discoidal, and posterior
one bigger and enlarged posteriorly; rim of ab-
dominal spiracle creamy yellow to yellow. Antero-
lateral margins of pronotum obliquely straight,
uniformly dentate; humeral angles produced lat-
erally, each margin dentate, and apically acute;
posterolateral and posterior margin straight and
smooth; calli behind with two short small tuber-
cles laterad to midline (Fig. 13). Legs. External
face of hind coxa with a large and robust tubercle;
hind femur medially incrassate, with three rows
of tubercles on dorsal surface, ventrally with two
rows of lateral spines; hind tibiae conspicuously
dilated. Scutellum longer than wide. Abdomen
slightly dilated, wider than hemelytra, maximum
width less than maximum width of pronotum
across humeral angles.
Genitalia. Posteroventral edge of genital cap-
sule simple, straight.
Coloration of females similar to holotype. Con-
nexival segments VIII and IX black, with anterior
third yellow to orange; dorsal abdominal seg-
ments VIII and IX orange yellow with posterior
margin black; genital plates orange with outer
border of paratergite VIII and IX black. Scutel-
lum wider than long; external face of hind coxae
blunt without tubercles; hind tibiae scarcely di-
lated. Plica located near the posterior border of
abdominal sternite VI.
Body surface rather dull, seldom shiny, almost
glabrous; bristle-like setae of antennal segments,
legs, and body surface scattered, short and ap-
pressed; antennal segment I with erect setae; fore
and middle leg with erect to suberect setae inter-


mixed with appressed setae; posterior third of
pronotal disc, scutellum, clavus, corium, acetabu-
lae, and posterior margin of prothorax, meso-
thorax, and metathorax sparsely to strongly
punctate; head, anterior third of pronotal disc,
calli, connexival segments, prosternum, mesos-
ternum and metasternum, upper anterior third of
propleura and metapleura, and abdominal sterna
impunctate; posterior third of pronotal disc with
scattered with minute tubercles; thorax with
minute tubercles near upper margin of each ace-
tabulum; genital segments of both sexes minutely
punctate and tuberculate.
Variation. 1: Posterior region of scutellum in-
cluding apex black, with anterolateral margins
creamy yellow, and basal and middle third chest-
nut orange. 2: Creamy yellow vitta along each
side of abdominal sterna III to VII complete and
characteristically enlarged posteriorly.
Measurements. S holotype first, then 9:
Head length 1.90, 1.80, width across eyes 2.40,
2.35, interocular space 1.55, 1.45, interocellar
space 0.88, 0.79, preocular distance 1.35, 1.20;
length of antennal segments: I, 3.85, 3.40, II,
3.80, 3.35, III, 2.90, 2.70, IV, 3.25, 3.00. Prono-
tum: Total length 5.68, 5.36, width across frontal
angles 2.70, 2.75, width across humeral angles
10.25, 9.85. Scutellar length 3.25, 3.15, width
3.20, 3.25. Maximum width of abdomen 9.50,
9.70. Total body length 23.83, 23.20.
Holotype. S Mexico: Sinaloa, 7mi S Culiacan,
23-VIII-1960 (R. L. Westcott). (CUIC). Paratypes.
1 S, 2 9: Same data as holotype. (CUIC, UNAM).
Etymology. From the Latin, atra, black, in
reference to the color of the anterior and posterior
lobs of the metathoracic peritreme.
Discussion. The laterally produced pronotal
shape is somewhat similar to that of M. buenoi
Hussey (Figs. 13, 14). However M. atra can be
easily separated by having the anterior and pos-
terior lobe of metathoracic peritreme entirely
black, the antennal segments orange, the bristle-
like setae of antennal segment I appressed, and
intermixed with erect setae, and the rims of the
abdominal spiracles creamy yellow to yellow. In
M. buenoi the anterior lobe of the metathoracic
peritreme is yellow with its inner margin nar-
rowly black, the antennal segments are not en-
tirely orange, antennal segment I is shorter (S
3.20, 9 2.75, against S 3.85, 9 3.40) with bristle
like setae appressed, and the rims of abdominal
spiracles black to brown.

Mozena nogueirana Brailovsky and Barrera,
New Species
Figs. 6, 8, 17, 23

Description. Male holotypee). Dorsal colora-
tion: head dark yellow hazel, with tylus, midline
stripe running from tylus to apex, and upper mar-
gin of antenniferous tubercles reddish brown; an-


March 2001




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