Title: Florida Entomologist
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Title: Florida Entomologist
Physical Description: Serial
Creator: Florida Entomological Society
Publisher: Florida Entomological Society
Place of Publication: Winter Haven, Fla.
Publication Date: 1996
Copyright Date: 1917
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Subject: Florida Entomological Society
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Insects -- Florida
Insects -- Florida -- Periodicals
Insects -- Periodicals
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General Note: Eigenfactor: Florida Entomologist: http://www.bioone.org/doi/full/10.1653/024.092.0401
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Shelly et al.: Methyl eugenol and B. philippinensis


METHYL EUGENOL AND MATING COMPETITIVENESS OF
IRRADIATED MALE BACTROCERA PHILIPPINENSIS
(DIPTERA: TEPHRITIDAE)

TODD SHELLY', SOTERO RESILVA2, MARLYN REYES AND HELEN BIGNAYAN3
1Hawaiian Evolutionary Biology Program, University of Hawaii
Honolulu, HI 96822

Philippine Nuclear Research Center, Commonwealth Avenue
Dillman, Quezon City, Philippines

3National Mango Research and Development Center
San Miguel, Jordan, Guimaras Island, Philippines

ABSTRACT

Males of many dacine tephritids are strongly attracted to methyl eugenol, a natural
compound occurring in a variety of plant species. Here, we investigated the effect of me
thyl eugenol on male reproductive behavior inBactrocera philippinensis (Drew & Han
cock). In mating trials conducted on caged host plants, irradiated males that fed on
methyl eugenol 3 or 5 days before testing had a mating advantage over wild males that
were not given access to the lure. Additional tests showed that feeding on methyl eu
genol increased male signaling activity (wing-fanning) and hence male attractiveness
to females. The tendency of males to feed on methyl eugenol following an initial expo
sure was also examined. Following an initial feeding on the lure, irradiated (but not
wild) males were less likely to feed in tests conducted 5 days later. The possibility of re
leasing methyl eugenol-exposed, irradiated males as a control strategy is discussed.

Key Words: Sterile insect technique, male replacement, fruit flies, male attractant

RESUME

Los machos de muchos tefritidos daquinos son fuertemenmte atraidos por el me
thyl eugenol, un compuesto natural que aparece en varias species de plants. Inves
tigamos aqui el efecto del methyl eugenol en el comportamiento reproductive de los
machos de Bactrocera philippinensis (Drew & Hancock). En ensayos de apareo condu
cidos en plants hospedantes enjaulas, los machos irradiados que se alimentaron de
eugenol de 3 a 5 dias antes del ensayo tuvieron ventajas de apareo sobre los machos
salvajes que no tuvieron acceso al cebo. Pruebas adicionales mostraron que la alimen
taci6n con methyl eugenol aument6 la actividad de emisi6n de senales (aleteo) y la
atracci6n de los machos hacia las hembras. La tendencia de los machos a alimentarse
de methyl eugenol luego de una exposici6n inicial tambien fue examinada. Luego de
una alimientaci6n inicial con el cebo, los machos irradiados (pero no los salvajes) ten
dieron menos a volver a alimentarse en las pruebas llevadas a cabo 5 dias mas tarde.
Es discutida la posibilidad de liberar machos irradiados expuestos al methyl eugenol
como estrategia de control.


Males of many dacine tephritids are strongly attracted to methyl eugenol, a com-
pound found naturally in a variety of plant species (Metcalf & Metcalf 1992). Though

















Florida Entomologist 79(4)


the basis of this attraction is still unknown, two lines of evidence suggest that methyl
eugenol plays a major role in male mating behavior by serving as a pheromonal pre
cursor. Working with Bactrocera opiliae (Drew & Hardy) and B. dorsalis (Hendel), re
spectively, Fitt (1981) and Nishida et al. (1988) reported that males fed on methyl
eugenol produced volatiles which contained metabolites of this compound, whereas
unfed males lacked these metabolites. Additionally, Shelly & Dewire (1994) showed
that wild males of B. dorsalis which ingested methyl eugenol exhibited increased sig
naling effort, signal attractiveness, and mating success compared with males not
given access to the lure. Additional tests similarly revealed that irradiated males ex
posed to methyl eugenol gained a mating advantage over unexposed wild males for up
to three weeks after feeding on the lure (Shelly 1995). Moreover, irradiated males ex
posed to methyl eugenol were less likely to be captured in lure-baited traps than were
unexposed irradiated males (Shelly 1995).
These results suggest that the methyl eugenol-male association could potentially
be incorporated in the sterile insect technique (SIT). Specifically, the abundance of
wild males could be reduced initially via male annihilation, and then lure-fed irradi
ated males could be released concurrent with continued male annihilation. If success
ful, this approach would effectively replace wild males with irradiated males and
thereby generate a high proportion of irradiated male by wild female matings.
The purpose of this study was to examine relationships between methyl eugenol
consumption and male mating behavior in Bactrocera philippinensis (Drew & Han
cock). Although field data are lacking, laboratory observations suggest that the repro
ductive behavior of this species is similar to that described for B. dorsalis (Kobayashi
et al. 1978, Arakaki et al. 1984, Shelly & Kaneshiro 1991): sexual activity is restricted
to a brief interval immediately preceding sunset, and males exhibit rapid wing-fan
ning (to facilitate pheromone dispersal) to attract females for mating. Three sets of ex
periments were conducted. First, we examined whether consumption of methyl
eugenol affected the mating performance of irradiated males relative to wild males.
Second, the effects of methyl eugenol consumption on male wing-fanning activity and
female attraction were monitored. Finally, we measured the tendency of males to feed
on methyl eugenol following initial exposure.

MATERIALS AND METHODS


Study Animals

Wild flies were reared from mango (Mangifera indica L.) fruits collected at various
localities on Guimaras Island, Philippines. Adults were separated by sex within 7
days of eclosion. Irradiated (150 Gy 2 days before adult emergence) and nonirradiated
mass-reared flies were obtained from the Philippines Nuclear Research Institute,
where the sexes were separated within 2-4 days of eclosion. Flies were held, and all
experiments were conducted, at the National Mango Research and Development Cen
ter (NMRDC), Guimaras Island, at 24-29C under a natural 12:12 (L:D) photoperiod.
Flies were provided water and a honey-protein hydrolysate mixture ad libitum.


Mating Tests

Most of the tests were conducted in two outdoor field cages (4 m by 2 m by 2 m) con
training potted guava (Psidium guajava L.) and mango plants. Thirty irradiated
males, 30 wild males, and 30 wild females were released into each cage between 1500
1530 hours, and mating pairs were collected from the onset of mating (1630-1730


December, 1996

















Shelly et al.: Methyl eugenol and B. philippinensis


hours) until dark (about 1830 hours). Irradiated males were 10-20 days old, and wild
flies were 21-35 days old. To distinguish male type, irradiated and wild males were
marked a minimum of 4 h prior to release by placing enamel paint on the thorax of
flies chilled for 60-90 s in a freezer. This procedure had no obvious adverse effects, and
males resumed normal activities within minutes of being marked.
Mating tests were occasionally conducted in a non-air-conditioned laboratory us
ing large (75 cm by 75 cm by 60 cm) and small (25 cm by 25 cm by 45 cm) screen cages.
We placed six irradiated males, six wild males, and six wild females in the large cages,
and three irradiated males, three wild males, and three wild females in the small
cages. The cages were placed by open, west-facing windows, thus ensuring natural
conditions of temperature and light. Room lights were turned off at 1530 hours. No
plants were placed in the screen cages.
We ran 5 different mating experiments. In the first, the mating success of wild and
irradiated males was compared in the absence of methyl eugenol. In the second, wild
males with no prior exposure to methyl eugenol (control) were tested against irradi
ated males exposed to methyl eugenol 1 day before the trial (treated). During expo
sure, 30-40 irradiated males were placed in large screen cages between 0930-1100
hours and given 2 h access to a cotton wick containing 1.5 ml of methyl eugenol. Feed
ing times of individual males were not recorded during the exposure period. Because
treated males in the second experiment had unexpectedly low mating success, we ex
posed irradiated males in the third experiment to the lure 1 day prior to testing but
removed males from the cotton wick after only 30 s of feeding. In the fourth and fifth
experiments, irradiated males were exposed to methyl eugenol for 2 h 3 and 5 days be
fore testing, respectively. Individual flies were used in only 1 trial.


Male Wing-Fanning and Female Attraction

Tests were conducted in large screen cages placed outside the laboratory building.
Each cage held 5-7 mango seedlings. Groups of four treated or four control males were
placed into transparent plastic cups (10 cm high by 6 cm diam). Treated males were
exposed to methyl eugenol for 2 h on the day preceding a trial following the above pro
cedure. Many small holes were made in the bottom of the cups, and the top was cov
ered with nylon screening.
In a given experimental cage, two cups, one containing treated males and one con
training control males, were suspended from the plants at 1600 hours. The cups were
placed at opposite sides of the cage (a minimum of 50 cm apart), and the positions of
treated and control males were alternated between days to compensate for any loca
tion effect. Fifteen females were then introduced into the cage. At the initiation of
wing-fanning, we recorded (1) the number of males wing-fanning in each cup and (2)
the number of females resting on each cup at 1 min intervals over a 30 min period. All
flies used in this experiment were nonirradiated, mass-reared individuals between
16-22 days old used only once.


Repeat Feeding on Methyl Eugenol

To monitor the incidence of repeat feeding on methyl eugenol, groups of 6 individ
ually marked males were placed in small screen cages along with a cotton wick con
training 1.5 ml of methyl eugenol. The wild males used were 22-35 days old, and the
irradiated males were 15-22 days old. Males were placed in the cages between 1000
1100 hours. The wick was introduced 20-30 min later, and the amount of time individ
ual males spent feeding on the wick was recorded over a 30 min period. The wick was

















Florida Entomologist 79(4)


then removed, and the flies were held in the cage (with food and water) for re-testing
5 days later using the same protocol.

Statistical Analyses

In the mating experiments, relatively low numbers of matings were observed per
cage per day; consequently, data were pooled within and between days. Deviation
from random mating was tested using the binomial test on the entire data set (using
normal approximation with test statistic Z and df=l). Over the 5 different mating ex
periments, tests in field cage tests were conducted on 4-10 different days. In compare
isons of male wing-fanning and female attraction, we used the non-parametric Mann
Whitney test (test statistic U) to avoid assumptions of normality and homoscedastic
ity (Zar 1974). Simple linear regression was calculated to describe the relationship be
tween female arrivals and male wing-fanning activity. The Student's t-test was used
to test for a difference between the slopes obtained for control vs. treated males. The
incidence of repeat feeding on methyl eugenol was examined using the G test (df=l)
with Yates correction. All statistical procedures followed Zar (1974).


RESULTS


Mating Tests

Results of the mating experiments are presented in Fig. 1. In the absence of me
thyl eugenol, wild and irradiated males had similar mating success (Z=0.5; P>0.05).
Contrary to expectations (see below), irradiated males exposed to methyl eugenol 1
day prior to testing obtained a disproportionately small number of matings both when
given 2 h access (Z 2.2; P<0.05) or when limited to 30 s feeding (Z 2.1; P<0.05). How
ever, increasing the length of the post-exposure interval greatly increased the mating
frequency of irradiated males, and they obtained 79% and 70% of all matings in tests
conducted 3 days (Z 4.6; P<0.001) and 5 days (Z 4.0; P<0.001) after exposure, respect
tively


Male Wing-Fanning and Female Attraction

Methyl eugenol had a pronounced effect on male wing-fanning activity (Fig. 2). A
mean of 42 instances of wing-fanning (maximum value possible=120 for four males
per cup over 30 checks) was recorded for cups with treated males compared to only 23
instances for cups containing control males (n=7 replicates; U=42; P<0.05). Also, more
females were sighted on cups with treated males than control males (Fig. 2). A mean
of 36 female sightings was recorded for cups with treated males, while only eight was
observed for cups with control males (U=49; P<0.001). This difference in female arriv
als apparently resulted from the increased wing-fanning of treated males and not to
a difference in signal attractiveness per se between control and treated males, be
cause the slopes relating female arrivals to male signaling were not significantly dif
ferent between control (Y 0.2+0.32X; r =0.40) and treated (Y 1.3+0.9X; r2 0.58)
males (t 1.5; P>0.05).


Repeat Feeding on Methyl Eugenol

Large, and statistically similar, proportions of both wild (25/62=40%) and irradi
ated (43/94=46%) males failed to feed on methyl eugenol during either the first or sec


December, 1996
















Shelly et al.: Methyl eugenol and B. philippinensis


70 Wild N O Irradiated

60-


0 50


E 40 --


10


Z 20--


10--


0
None 2 h/1 d 30 s/1 d 2 h/3 d 2 h/5 d

Methyl eugenol exposure

Fig. 1. Number of matings obtained by wild and irradiated males. Designations
along the abscissa refer to different exposure regimes for irradiated males; wild males
were not exposed to methyl eugenol in any test. First value represents duration of ex-
posure period, and second value represents interval length between exposure period
and testing. See text for additional details.


ond exposure periods (G=0.2; P>0.05). Moreover, among wild males there was no
reduction in the incidence of feeding following an initial feeding: 35% (22/62) of wild
males fed during the first exposure, and of these 32% (7/22) fed again during the sec-
ond exposure (G=0.2; P>0.05). In contrast, among irradiated males initial feeding re-
sulted in a reduced tendency to feed again. Over 40% (41/94) of irradiated males fed
during the first exposure period, but of these only 24% (10/41) also fed during the sec-
ond exposure period (G=6.0; P<0.05).
For both types of males, the likelihood of repeat feeding was inversely related to
feeding duration during the initial exposure. Feeding durations in the first period
were significantly longer for individuals that fed during the first period only than for
individuals that fed during both periods for both wild (5.8 vs. 3.1 min, respectively;
U=91.5; n,=15, n =7) and irradiated (5.7 vs. 2.9 min, respectively; U=241; n,=31,
n =10) males (P<0.01 in both cases; Mann-Whitney test). These data suggest that the
difference in the incidence of repeat feeding noted above between wild and irradiated
males resulted from the fact that, among individuals that fed only briefly at first, wild
males were more likely to feed again than irradiated males. Though samples were
small, this trend is indicated: among males that fed very little initially (<3 min), 80%
(4/5) of wild males were repeat feeders compared to only 30% (3/10) of irradiated
males.
















Florida Entomologist 79(4)


60 Control x Treated


50-
/*

g40- X X

"Z 30*--,,


E
u_ 20-X


10 0
10

II I

0 10 20 30 40 50 60

Male wing-fanning

Fig. 2. Relationship between female sightings and wing fanning for control (*)
and treated (*) males. Each point represents a cup that contained four males. The ab
scissa represents the total number of wing fanning instances recorded for all four
males per cup over the 1 min observations. The ordinate represents the total number
of female sightings on a cup over the 1 min observations.

DISCUSSION

The present study reveals that, as in B. dorsalis (Shelly 1995), methyl eugenol
greatly increased the mating success of irradiated B. philippinensis males relative to
control wild males. Nonetheless, several differences were evident between these spe
cies. First, the positive effect of methyl eugenol on mating performance was evident
sooner in B. dorsalis than B. philippinensis. Male B. dorsalis given 2 h access to the
lure had low mating success when tested on the same day but enhanced mating suc
cess when tested 1 day later, and males whose feeding was restricted to 30 s had a
mating advantage when tested on the same day (Shelly & Dewire 1994). In B. philip
pinensis, however, males in both treatment types had low mating frequency even 1
day after exposure. Initially, at least, methyl eugenol appears to reduce male sexual
activity (e.g., wing fanning, Shelly & Dewire 1994), and it appears that these negative
effects are longer lasting in B. philippinensis than B. dorsalis.
In addition, methyl eugenol influenced both signaling effort and signal attractive
ness in B. dorsalis (Shelly & Dewire 1994), but apparently enhanced only signaling ef
fort in B. philippinensis. However, the relative difference in female sightings vs. male
wingfanning (Fig. 2) is quite large between control vs. treated males (0.32 vs. 0.9, re
spectively), and a larger sample may have shown a statistically significant difference
in attractiveness.


December, 1996

















Shelly et al.: Methyl eugenol and B. philippinensis


Third, the level of feeding activity on methyl eugenol differed between the species.
In tests conducted in the same manner, over 90% (126/134) of B. dorsalis males (mass
reared, non irradiated; Shelly 1994) fed on the lure during at least 1 of 2 exposure pe
riods compared to only 57% (88/156) of B. philippinensis males (wild and mass-reared,
irradiated males combined; G=56.8; P<0.001; G test with Yates correction). However,
irradiated males of both B. dorsalis (Shelly 1995) and B. philippinensis showed a re
duced tendency to re-visit a methyl eugenol source following an initial feeding.
Despite the lower incidence of methyl eugenol feeding, the enhanced mating suc
cess and low tendency for repeat feeding of lure-fed irradiated males suggest that B.
philippinensis is a potential candidate for the method of "male replacement" men
tioned above. This strategy has several potential merits. Exposure to methyl eugenol
is a logistically simple and relatively inexpensive means to increase the mating com
petitiveness of irradiated males. Also, lure-induced enhancement of mating perform
mance may compensate for genetic changes accompanying colonization that lessen
the attractiveness of mass-reared males to wild females (Calkins 1984). Perhaps the
greatest obstacle to implementation is the fact that Bactrocera males do not respond
to methyl eugenol until sexually mature (Metcalf 1990). Consequently, additional
space and rearing supplies would be needed to hold closed adults for 7-10 days prior
to exposure and release.
The present study furnishes evidence for another tephritid species in which male
attractants, or structurally similar compounds, function in mate attraction and mat
ing success. Previous studies with cue lure and B. cucurbitae (Coquillett) (Shelly &
Villalobos 1995) and trimedlure and Ceratitis capitata (Wiedemann) (Shelly et al.
1996) also reveal a positive relationship between exposure to male lure and male mat
ing performance. Interspecific variation is apparent in (1) the time elapsed between
exposure and heightened mating success, (2) the "potency" of the lure in terms of the
duration of mating advantage, and (3) the effect of the lure on signaling effort and sig
nal quality. Clearly, data from more species are required before any pattern emerges
regarding general relationships between parapheromones and male mating behavior.
Nonetheless, the few existing studies will, we hope, stimulate additional research in
this area from both basic and applied perspectives.

ACKNOWLEDGMENTS

We thank Carlos Aleta, Hernani Golez, Jorge Hendrichs, and Eugenia Manoto for
their gracious cooperation and support during this research. We thank Sofia Covache,
Erdie Gaitan, Jimmy Macahilo, Percival Orilla, Helen Segovia, Sylvia Talaban, Mila
gros Tanaleon, and Nenita Zamora for assistance. TES expresses special gratitude to
Sofia Covache for arranging travel and lodging on Guimaras Is. This research was
supported by the International Atomic Energy Agency and by the USDA-CSRS
(9401860).

REFERENCES CITED

ARAKAKI, N., H. KUBA, AND H. SOEMORI. 1984. Mating behavior of the oriental fruit
fly, Dacus dorsalis Hendel (Diptera: Tephritidae). Appl. Entomol. Zool. 19: 42
51.
CALKINS, C. 0. 1984. The importance of understanding fruit fly mating behavior in
sterile male release programs (Diptera: Tephritidae). Folia Entomol. Mex. 61:
205-213.
FITT, G. 1981. The influence of age, nutrition, and time of day on the responsiveness
of male Dacus opiliae to the synthetic lure methyl eugenol. Entomol. Exp. Appl.
30: 8390.

















Florida Entomologist 79(4)


KOBAYASHI, R. M., K. OHINATA, D. L. CHAMBERS, AND M. S. FUJIMOTO. 1978. Sex
pheromones of the oriental fruit fly and the melon fly: mating behavior, bioas
say method, and attraction of females by live males and by suspected phero
mone glands of males. Environ. Entomol. 7: 107-112.
METCALF, R. L. 1990. Chemical ecology of dacine fruit flies (Diptera: Tephritidae).
Ann. Entomol. Soc. America 83: 1017-1030.
METCALF, R. L., AND E. R. METCALF. 1992. Plant kairomones in insect ecology and
control. Chapman and Hall. New York. 168 p.
NISHIDA, R., K. H. TAN, M. SERIT, N. H. LAJIS, A. M. SUKARI, S. TAKAHASHI, AND H.
KUKAMI. 1988. Accumulation of phenylpropanoids in the rectal glands of males
of the oriental fruit fly, Dacus dorsalis. Experientia (Basel) 44: 107-112.
SHELLY, T. E. 1994. Consumption of methyl eugenol by male Bactrocera dorsalis
(Diptera: Tephritidae): low incidence of repeat feeding. Florida Entomol. 77:
201-208.
SHELLY, T. E. 1995. Methyl eugenol and the mating competitiveness of irradiated
male Bactrocera dorsalis (Diptera: Tephritidae). Ann. Entomol. Soc. America
88: 883-886.
SHELLY, T. E., AND A. DEWIRE. 1994. Chemically mediated mating success in male ori
ental fruit flies, Bactrocera dorsalis (Diptera: Tephritidae). Ann. Entomol. Soc.
America 87: 375-382.
SHELLY, T. E., AND K. Y. KANESHIRO. 1991. Lek behavior of the oriental fruit fly, Da
cus dorsalis, in Hawaii (Diptera: Tephritidae). J. Insect Behav. 4: 235-241.
SHELLY, T. E., AND E. M. VILLALOBOS. 1995. Cue lure and the mating behavior of male
melon flies (Diptera: Tephritidae). Florida Entomol. 78: 473-482.
SHELLY, T. E., T. S. WHITTIER, AND E. M. VILLALOBOS. 1996. Trimedlure affects mat
ing success and mate attraction in male Mediterranean fruit flies. Entomol.
Exp. Appl. 78: 181-185.
ZAR, J. H. 1974. Biostatistical analysis. Prentice-Hall, Inc. Englewood Cliffs, NJ.


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December, 1996
















Florida Entomologist 79(4)


COMPARISON OF CONVENTIONAL AND BIOLOGICAL
CONTROL INTENSIVE PEST MANAGEMENT PROGRAMS ON
EGGPLANT IN NEW JERSEY

GEORGE C. HAMILTON AND JAMES LASHOMB
Department of Entomology, P.O. Box 231, Cook College
Rutgers University, New Brunswick, NJ 08903

ABSTRACT

Adoption of biological control and Integrated Pest Management programs by grow
ers depends on adequate control of pests while remaining cost effective. Some New
Jersey eggplant growers follow a biological control intensive pest management
(BCIPM) program, utilizing the egg parasitoid Edovum puttleri Grissell for the con
trol of Colorado potato beetle. This study evaluates the profitability of the BCIPM pro
gram based on comparisons of planting and insecticide application costs, and yield
information from conventional and BCIPM growers during the 1993 and 1994 grow
ing seasons. On average, BCIPM growers utilized less insecticide and made fewer ap
plications than conventional growers to control Colorado potato beetles. Differences
for the control of aphids, eggplant flea beetles, and two-spotted spider mites were less


December, 1996

















Hamilton & Lashomb: Conventional and BCIPM Programs 489

evident. Each year, BCIPM growers harvested increased levels of higher quality fruit
when compared with conventional growers, while incurring similar production costs.
These differences resulted in higher per hectare crop values, increased monetary re
turns, and a more environmentally friendly production system for BCIPM growers.

Key Words: Eggplant, Colorado potato beetle, Edovum puttleri, BCIPM, profitability


RESUME

Los granjeros adoptan programs de control biol6gico e integrado de plagas
cuando dichos programs produce un adecuado control de las plagas a un costo efec
tivo. Algunos productores de berenjena de New Jersey siguen un program intensive
de control biol6gico e integrado, utilizando el parasitoide de huevos Edovum puttleri
Grissell para el control del escarabajo de la papa de Colorado. En este studio se eva
lua la rentabilidad del program de manejo integrado, sobre la base de comparaciones
de costo de plantaci6n, aplicaci6n de insecticides y rendimiento, en granjeros conven
cionales y en granjeros que aplican el program de manejo integrado para el control
del escarabajo de Colorado. Las diferencias en el control de afidos, crisomelidos, y aca
ros de dos manchas fueron evidentes. Cada ano, los granjeros que utilizaron el pro
grama de manejo integrado aumentaron la producci6n de frutos de alta calidad en
comparaci6n con los granjeros convencionales, incurriendo en los mismos costs de
producci6n. Los granjeros con manejo integrado tuvieron mas altos valores de produce
ci6n por hectarea y mayor rentabilidad, ademas de un sistema producci6n ambiental
mente mas sano.





New Jersey is a major producer of vegetables in the United States. In 1990, 404.7
hectares of eggplant (Solanum melongena L.) were planted with yields averaging
848.11 kg per hectare (NJ Dept. Agriculture 1991). Of the eleven most common vege
tables grown in New Jersey during 1990, eggplant ranked second in total dollar value
($2,188,000). The use of pesticides is also correspondingly high (Hamilton & Meyer
1992). This use pattern represents primarily insecticides applied to control the major
insect pest in eggplant, the Colorado potato beetle, Leptinotarsa decemlineata (Say),
and various fungicides. Feeding by larval and adult Colorado potato beetles can result
in significant plant injury and yield losses (Cotty & Lashomb 1982).
Conventional control of Colorado potato beetles on eggplant and potato has been
accomplished by weekly applications of insecticides. Beginning in the 1970's, this led
to resistance by Colorado potato beetles to nearly all of the chemicals available (For
gash 1985). Despite the development of new insecticides, this situation further inten
sified during the 1980's. In response, a biological control intensive pest management
program (BCIPM) was developed utilizing the egg parasitoid Edovum puttleri Gris
sell (Lashomb 1989). The program relies on bi-weekly scouting of fields, six weeks of
parasitoid releases, and limited insecticide usage to maintain Colorado potato beetle
populations below economically damaging levels. To date, the program has been im
plemented by the New Jersey Department of Agriculture on 10% of New Jersey's total
eggplant acreage.
To gain acceptance of any pest management program, growers must have confi
dence that it will work and be cost effective (Headley 1975). The BCIPM program has
been shown to effectively control Colorado potato beetles (Lashomb 1989), but a prof
itability comparison with conventional practices has not been conducted. This study
provides the cost/return information needed to make this comparison.

















Florida Entomologist 79(4)


MATERIALS AND METHODS

In 1993 and 1994, all growers participating in the eggplant BCIPM program (10 in
1993; 8 in 1994) and seven conventional growers were asked to participate in the
study. Conventional growers were selected based on their geographic proximity to
BCIPM growers and the forecast of planting 'Harris Special' eggplant (industry stan
dard). Each year prior to planting, growers provided the numbers of hectares of 'Har
ris Special' eggplant that would be grown and agreed to supply application records
[date, pest(s) treated for, material and rate used, total amount applied, and number
of hectares treated] for all insecticides applied during the growing season. Growers
also agreed to provide harvest information, i.e., number of boxes packed per hectare
by grade class (#1, #2, and large) for each harvest date.


Production Costs

Standard production costs per hectare for plant material ($220.20), fertilizer
($46.97), lime ($9.70), supplies ($408.12), and labor ($563.03-planting, fertilizer and
lime applications, and harvesting) were obtained from information developed by
Dhillon & Latimer (1986) for New Jersey eggplant production. Standard costs for
BCIPM growers also included a $40.47 per hectare charge for the parasitoid. This
charge is mandatory for growers in the program and is assessed to cover the cost of
parasitoid rearing, weekly parasitoid-releases (2,700 per ha), and bi-weekly scouting
of fields.
Cost data for the insecticide applied each year were developed from information
(dollars per kg AI) supplied by 3 local pesticide distributors. Product costs were calcu
lated on a per hectare basis for azinphos methyl ($3.31 Guthion", Bayer, Kansas
City, MO), Bacillus thuringiensis tenebrionis (Btt) ($5.66-M-One", Mycogen, San Di
ego, CA; $8.01-Novodor", Novo-Nordisk, Franklinton, NC), cryolite ($0.89-Kryo
cide", Elf Atochem, Philadelphia, PA), endosulfan ($2.72-Thiodan", FMC,
Philadelphia, PA), esfenvalerate ($82.55-Azana XL", E.I. Dupont, Wilmington, DE),
fenbutatin oxide ($18.06-Vendex", E.I. Dupont, Wilmington, DE), methomyl
($4.54-Lannate L", E.I. Dupont, Wilmington, DE), mevinphos ($10.16-Phosdrin",
Amvac Chemical, Los Angeles, CA), oxamyl ($5.87-Vydate L", E.I. Dupont, Wilming
ton, DE), PBO ($4.91-Butoxide", Fairfield American, Frenchtown, NJ), permethrin
($24.05-Ambush", Zeneca, Wilmington, DE; $38.25-Pounce", FMC, Philadelphia,
PA), pyrethrins/rotenone ($10.22-Pyrellin", Webb Wright Corp., Ft. Myers, FL), and
rotenone ($2.30-Rotenox", Fairfield American, Frenchtown, NJ). Labor costs associ
ated with the application of insecticides were set at $15 per hectare per application
(Dhillon & Latimer 1986).
Seasonal eggplant prices were determined using weekly pricing data for the years
1980 to 1994 obtained from the New Jersey Department of Agriculture, Agricultural
Statistics office. Using this information, mean market prices were set at $8.00 per box
for #1 fruit, $4.00 per box for #2 fruit, and $6.00 per box for large fruit.


Statistical Analysis

The data collected each year were analyzed using analysis of variance (ANOVA).
Mean separation tests (LSD; P<0.05) were conducted to determine differences be
tween the two farming regimes (SAS 1994). An economic analysis, using per hectare
costs and returns, was conducted to assess the differences in profitability between
each system.


December, 1996

















Hamilton & Lashomb: Conventional and BCIPM Programs 491

RESULTS AND DISCUSSION

A total of 19.83 (1.98 ha per grower) and 14.73 (2.10 ha per grower) hectares were
grown by BCIPM and conventional growers, respectively, in 1993. Comparable acre
ages were again grown by both groups the following year (BCIPM-22.87 ha, 2.87 ha
per grower; conventional-21.04 ha, 2.99 ha per grower).
Conventional growers applied a total of 52.81 kg AI per hectare of insecticide/aca
ricide in 1993 and 17.84 kg AI per hectare in 1994 (Table 1). Growers in the BCIPM
program utilized lower total amounts each year, applying 30.50 kg AI per hectare and
14.07 kg AI per hectare in 1993 and 1994, respectively. These materials were applied
to control four pests: Colorado potato beetle; green peach aphid, Myzus persicae
(Sulzer); eggplant flea beetle, Epitrixfuscula Crotch; and two-spotted spider mite, Tet
ranychus urticae (Koch). Each year, the amount applied to control Colorado potato
beetles were higher for conventional growers. Conventional growers also applied
higher amounts to control aphids, flea beetles and two-spotted spider mite than
BCIPM growers in 1993 but applied similar amounts in 1994. The difference in the to
tal amounts applied is due to the types of insecticides used. The data show that con
ventional growers apply a wider variety of materials, while BCIPM growers restricted
their applications for Colorado potato beetle control to primarily the use of rotenone
and PBO. Rotenone and PBO are less harmful to Edovum puttleri than other avail
able insecticides (Hamilton et al., in press) and are recommended once parasitoid re
leases are begun.
BCIPM growers made significantly fewer applications (about 2.0 during parasitoid
releases) and treated significantly fewer hectares to control Colorado potato beetle
than conventional growers (Table 2). BCIPM growers also applied less active ingredi
ent, both in terms of seasonal amounts and amounts per hectare. The total seasonal
costs associated with these applications were significantly lower for BCIPM growers
each year; however, the per hectare costs were significantly lower in 1994 only. Unlike
the applications made to control Colorado potato beetles, those made to control
aphids, flea beetles, and mites varied between years. BCIPM growers made more ap
plications and applied more material per hectare in 1993 but treated less acreage us
ing less material per hectare in 1994. Both years, BCIPM growers treated less acreage
and applied lower total amounts. The cost of these applications was also different.
Each year, while the total cost incurred by conventional growers was higher, the per
hectare costs were lower.
BCIPM growers experienced higher yields than conventional growers, harvesting
significantly more #1 and #2 eggplants in 1993 and 1994 (Table 3). Conventional
growers, however, produced more large fruit. The difference in yields of #1 and #2 fruit
indirectly suggests that BCIPM growers produced higher quality fruit. Grade levels
in eggplant are determined by several factors including fruit size, fruit color and the
absence of damage. Visible feeding damage as small as one bite to the flesh or calyx
of the fruit causes a fruit to be culled. Less frequent occurrence of culling in BCIPM
fields due to reduced Colorado potato beetle populations would explain the yield dif
ferences observed. The higher number boxes produced per hectare by BCIPM trans
lated into gross profits for BCIPM growers as well. Each year the per hectare crop
value was significantly higher for BCIPM growers (+$521.40 in 1993, +$442.27 in
1994).
Standard costs (i.e., plant material, fertilizer, etc.) for the two programs were as
sumed identical except for the added cost incurred by BCIPM growers for scouting
and rearing/release of the parasitoid (Table 4). Total insecticide costs (AI and labor
costs) were different each year between the two groups. In 1993, BCIPM growers
spent $92.00 more per hectare than conventional growers; however, in 1994 BCIPM























Florida Entomologist 79(4) December, 1996




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Hamilton & Lashomb: Conventional and BCIPM Programs 495

TABLE 4. PROFIT/LOSS ANALYSIS FOR CONVENTIONAL AND BCIPM GROWERS, 1993 AND
1994.

Cost-Value (dollars) per Hectare

1993 1994

Item Conventional BCIPM Conventional BCIPM

Costs
Standard 1,250.02 1,290.49 1,250.02 1,290.49
Insecticides 195.90 288.20 208.90 115.30

Total 1,445.92 1,578.69 1,458.92 1,405.79
Crop Value 2,902.47 3,423.87 2,450.21 2,892.48
Profit 1,456.55 1,845.18 1,041.10 1,486.69


growers spent $93.60 less. Using the costs and crop values calculated for the 1993 and
1994 growing seasons, an analysis of profit or loss showed that BCIPM growers made
a greater profit than conventional growers. The profit level was 27% and 43% higher
in 1993 and 1994, respectively.
A valuable outcome of an effective IPM program can be a reduction in pesticide us
age (Pedigo 1996). This effect has been documented for IPM programs in several other
crops including anturiums and tomato (Hara et al. 1990; Trumble & Alvarado-Rod
riguez 1993). The data reported here show that this reduced insecticide use is occur
ring with the BCIPM program for eggplant. Overall, 42.2% and 21.1% more pesticides
were applied by conventional growers in 1993 and 1994, respectively. Accordingly,
growers in the BCIPM program on average treated their crop 42.4% and 59.1% fewer
times in 1993 and 1994, respectively, for Colorado potato beetle control than conven
tional growers.
In determining the benefits of an BCIPM program, yield levels and costs must be
evaluated. If reducing pesticide usage results in reduced profitability, growers will have
little incentive to adopt a new program (Rajotte 1993). This study provides evidence
that an advantage, other than reduced pesticide levels, is gained by participating in the
BCIPM program. Each year, BCIPM growers produced more fruit per hectare and ex
perienced higher net profits (value of fruit at harvest minus production cost) when com
pared to conventional growers. Trumble & Alvarado-Rodriguez (1993) report similar
results for an IPM program developed for tomatoes. Their program, which uses inten
sive sampling, parasitoid releases, and selective use of pesticides, resulted in higher net
profits ($304-$579 per ha) when compared to standard control practices.
The differences in the input (i.e., standard costs, scouting, insecticides, etc.) and
profits shown between the two programs would not justify using conventional prac
tices as opposed to enrollment in the state BCIPM program. The data indicates that
growers involved in the state BCIPM program can spend less time and money on pes
ticide applications and incur higher returns on their investment.


ACKNOWLEDGMENTS

The authors thank Wayne Hudson of the New Jersey Department of Agriculture,
Phillip Alampi Beneficial Insect Laboratory for help in data collection, Rachael Di

















Florida Entomologist 79(4)


Palma for data entry, and Randy Gaugler for his critical review of this manuscript.
This study was supported by USDA CSREES PIAP Special Project Agreement 93
EPIX 1 00116. New Jersey Agricultural Experiment Station Publication Number D
08930-12-95, supported by state funds and U.S. Hatch Act.


REFERENCES CITED

COTTY, S., AND J. LASHOMB. 1982. Vegetative growth and yield response of eggplant
to varying first generation Colorado potato beetle densities. J. New York Ento
mol. Soc. 90:220-228.
DHILLON, P. S., AND R. G. LATIMERR 1986. Costs of producing fresh market vegetables
in southern New Jersey-1986 update. New Jersey Agricultural Experiment
Station Bulletin P-02131 1 86. 65 pp.
FORGASH, A. J. 1985. Insecticide resistance in the Colorado potato beetle, pp. 33-53.
in D. N. Ferro and R. H. Voss [eds.], Proceedings of the symposium on Colorado
potato beetle. XVIIth International Congress of Entomology. Research Bulletin
#704, Massachusetts Agricultural Experiment Station, Amherst, MA.
HAMILTON, G. C., J. H. LASHOMB, AND J. M. PATT. In Press. Impact of selected insec
ticides used in eggplant production on Edovum puttleri Grissell (Hymenoptera:
Eulophidae). J. Entomol. Sci.
HAMILTON, G. C., AND L. MEYER 1992. Agricultural pesticide use in New Jersey-a
survey of private applicators in 1985 and 1988. Rutgers Cooperative Extension
Bulletin E155. 12 pp.
HARA, A. R., W. T. NISHIJIMA, J. D. HANSEN, B. C. BUSHE, AND T. Y. HATA. 1990. Re
duced pesticide use in an IPM program for anthuriums. J. Econ. Entomol. 83:
1531-1534.
HEADLEY, J. C. 1975. The economics of pest management, pp. 75-99 in R. L. Metcalf
and W H. Luckman [eds.], Introduction to insect pest management. John Wiley
& Sons, NY. 587 pp.
LASHOMB, J. 1989. Use of biological control measures in the intensive management of
insect pests in New Jersey. American J. Alternative Agric. 3: 7783.
NEW JERSEY DEPARTMENT OF AGRICULTURE. 1991. Annual Report Agricultural Sta
tistics. Trenton, NJ. 96 pp.
PEDIGO, L. 1996. Entomology & Pest Management. Prentice Hall, Upper Saddle
River, NJ. 679 pp.
RAJOTTE, E. G. 1993. From profitability to food safety and the environment: Shifting
the objectives of IPM. Plant Dis. 77: 296-299.
SAS INSTITUTE. SAS/STAT guide for personal computers. 1994. Cary, NC. 378 pp.
TRUMBLE, J. T., AND B. ALVARADO-RODRIGUEZ. 1993. Development and economic
evaluation of an IPM program for fresh market tomato production in Mexico.
Agric., Ecosystems and Environ. 43: 267-287.


December, 1996

















Hu & Frank: Effect ofArthropod Community on Horn Flies 497

EFFECT OF THE ARTHROPOD COMMUNITY ON
SURVIVORSHIP OF IMMATURE HAEMATOBIA IRRITANS
(DIPTERA: MUSCIDAE) IN NORTH CENTRAL FLORIDA

G. Y. Hu AND J. H. FRANK
Department of Entomology and Nematology, University of Florida
Gainesville, FL 32611-0620, USA

ABSTRACT

Field mortality of horn flies caused by the arthropod community was tested by
seeding colony-reared horn fly (Haematobia irritans L.) eggs underneath artificial
cattle pats placed in the field and collecting the emerging flies using cone traps. Mean
numbers of horn flies that emerged from pats exposed to the whole arthropod commu
nity during the developmental period of the immature stages were significantly lower
than those from pats isolated from all members of the community except Solenopsis
invicta Buren. The community-caused mortalities of horn flies were 75.9% and 66.7%
in July and August 1992, respectively, with an overall average of 71.3%. Predation by
S. invicta raised mortality to at least 93.9%. These results suggest that the other ar
thropods in cattle dung played an important role in reducing horn fly populations in
north-central Florida.

Key Words: Fire ants, insect community, mortality, cattle dung, horn fly

RESUME

Fue evaluada la mortalidad de la mosca Hematobia irritans L. causada por artr6
podos depredadores en esti6rcol rociando huevos de H. irritans en tortas de esti6rcol
artificial. Las tortas de esti6rcol fueron luego expuestas a la comunidad de artr6podos
o aisladas de forma que los artr6podos, con la excepci6n de Solenopsis invicta Buren,
no tuviesen acceso a ellas. Las moscas sobrevivientes de cada una de las tortas fueron
capturadas en trampas de embudo. El numero promedio de moscas obtenidas en las
tortas de esti6rcol expuestas a toda la comunidad de artr6podos fue significativa
mente mas baja que el de las tortas aisladas de la comunidad de artr6podos. La mor
talidad de campo causada por artr6podos fue de 75.9% y 66.7% en Julio y Agosto de
1992, respectivamente, con una mortalidad promedio total de 71.3%. La depredaci6n
por S. invicta aument6 la mortalidad al nivel del 93.9% por lo menos. Los resultados
obtenidos sugieren que otros artr6podos en el esti6rcol juegan un papel muy impor-
tante en el control poblacional de la mosca en la region norte centro de la Florida.





The horn fly, Haematobia irritans L., is a widespread, economically important pest
of cattle (Morgan & Thomas 1974, 1977). The blood loss and annoyance due to bites of
the adult flies cause a reduction of weight gain to cattle. Annual losses to the cattle in
dustry in the United States attributed to this pest have been estimated to reach $870
million (Kunz et al. 1991). In Florida, Butler (cited in Hogsette & Koehler 1986) esti
mated an annual loss of about $61 million from horn flies. Control of this pest typi
call has been by using chemical insecticides, but widespread insecticide resistance
has occurred throughout the country (Sheppard 1990). In addition, residues from
feed-through insecticides used for controlling dung-inhabiting flies adversely affect
the abundance of biological control agents in dung (e.g., Scarabaeidae and Staphylin
idae) (Fincher 1992, Madsen et al. 1990, Wall & Strong 1987).

















Florida Entomologist 79(4)


Horn fly larvae are coprophagous and develop only in fresh cattle dung (Macqueen
& Beirne 1975, Skidmore 1991). The dung arthropod community has been shown to
reduce horn fly populations in the USA (Blume et al. 1970, Thomas & Morgan 1972,
Kunz et al. 1972, Roth 1989), Canada (Macqueen & Beirne 1975) and Australia (Fay
et al. 1986, 1990). In Florida, Escher (1977) and Butler et al. (1981) reported parasit
ism of horn flies, but there have been no studies on the effect of the whole arthropod
community on horn fly survivorship. During a survey of the arthropod community in
cattle dung in Florida pastures, more than 220 species of arthropods were collected
(Hu 1995). The objective of this study was to estimate the effect of the arthropod com
munity on survivorship of immature horn flies in north central Florida.

MATERIALS AND METHODS

Laboratory Studies on Horn Fly Survivorship

Survivorship of horn flies was studied in the laboratory before initiating field stud
ies. Horn flies were obtained from the colony maintained by J. F. Butler, Department
of Entomology /Nematology, University of Florida. Standard colony rearing methods
were developed by Greer (1975) and modified by Okine & Butler (1995). Constituents
of the larval medium included cow manure which had been frozen and then allowed
to thaw, and pelleted peanut hulls. Adults were fed bovine blood and maintained in an
environmental chamber at 27+3'C and 75+5% RH with continuous light.
Manure used for experiments was collected within 30 min after its deposition and
frozen until needed. Manure processed this way contained no living insects when held
>3 wk at 25'C.
Artificial pats were prepared by following the procedure of Thomas & Morgan
(1972). Horn fly eggs <4 hr old were suspended in water and pipetted onto paper towel
strips (6 cm long x 2 cm wide; 25 eggs per strip) moistened with water. A metal hoop,
20.3 cm diam and 5.1 cm high, was placed on a grass turf in a large metal pan. The
area within the hoop was moistened with water. Four paper towel strips (100 total
eggs) were placed on the grass and spaced equally around the perimeter of the hoop.
The area within the hoop was covered with manure which had been taken from stor
age and thawed under room temperature. The hoop was removed, leaving a simulated
manure pat approximately 25 cm diam x 5 cm high. The simulated manure pats were
held in a rearing room for 7-8 days and then covered with cone traps (see below) to col
lect emerging horn flies. Six replicates were made. Parameters measured were per
cent egg hatch after 24 h, and adult survival based on the original number of eggs.

Field Studies on Horn Fly Mortality

Field mortality of the horn fly was evaluated during July and August 1992 in a beef
range where an arthropod survey was conducted at the same time. Horn fly eggs from
the laboratory colony were used. The manure collection and artificial pat formation
techniques used for laboratory survival studies were also used in the field studies. Fe
male horn flies oviposit only on fresh cattle droppings (Bruce 1964, Skidmore 1991),
so artificially formed pats had no attraction to horn flies. No horn flies were found to
land on artificially formed pats in the fields.
Two trials were conducted, one each in July and August 1992. Twenty simulated
manure pats were formed for each trial. They were placed in a line outside the fence
surrounding the pastures (3 pastures in total) that contained cattle. Adjacent pats
were separated by 10 m. Egg-seeding procedures (100 eggs per pat) followed those for
laboratory survival studies. Ten pats (odd numbers) were at first left uncovered to al


December, 1996

















Hu & Frank: Effect ofArthropod Community on Horn Flies 499

low other arthropods to come to the dung and then covered by cone traps on the 8th
day after egg-seeding; the other 10 (even numbers) were covered immediately after
egg-seeding. The arrangement of the pats was a a randomized complete block design,
each pair of pats (adjacent to each other) containing a covered (treatment) and an un
covered (control) pat.
The cone traps (Fig. 1) used for covering the seeded cattle pats were constructed of
a wire frame and wrapped with a fine Saran" screen of 2 mesh per mm. Traps were 30.5
cm diam (bottom) and 50.8 cm high. A circular hole (5 cm diam) was cut through the
screen on the top of the trap, and an 8.9 cm high 5.1 cm diam vial was screwed on (the
lid of the vial was perforated, then glued and riveted to the trap) to collect horn flies
that emerged from the pat. The mouth of the vial was fitted with a Sararf screen fun
nel to prevent insects from escaping back into the trap. The vials were checked daily
from the 8th day after egg-seeding until two days after the last horn flies were found.
The cone traps excluded insects that flew to the dung pats. Because they were slightly
embedded in soil, they excluded insects that walked, but not those that tunneled.
Differences in horn fly emergence between treatments were analyzed by a paired
Student's t test (SigmaPlot 1994). Before the t test was conducted, the numbers of
horn flies were transformed by log (n+1) to satisfy equal variance and normality re
quired by the t test (Marks 1990).

RESULTS AND DISCUSSION

Laboratory Horn Fly Survival

Hatch of horn fly eggs ranged from 78 to 94%, with an average of 85.7+4.1% (SE)
when the eggs were distributed on paper towel strips inserted into the artificial pat


Fig. 1. Cone traps used for covering cattle pats to collect horn flies and other flies
that emerged from the pats.
















Florida Entomologist 79(4)


for 24 hours. Survival of the eggs to the adult stage ranged from 22-41%, with an av
erage of 29.8+6.15.

Fauna-induced Field Horn Fly Mortality

July 1992 trial. Horn flies emerged from the 9th to 13th day after their eggs were
seeded under the artificial pat, with peak emergence occurring on the 10th and 11th
day. An average of 2.90.95 (SE) horn flies emerged from the pats covered by cone
traps (range 0-8); an average of 0.70.3 (SE) horn flies emerged from the pats exposed
to other arthropods (range 0-3). This difference was significant (t3.09, df=9, P<0.01;
Fig. 2). Horn fly numbers were reduced by an average of 75.86% in the uncovered pats
compared with the covered ones.
August 1992 trial. An average of 3.00.56 (SE) horn flies emerged from the pats
covered by cone traps (range 0-5); an average of 1.00.26 (SE) flies emerged from the
pats exposed to other arthropods (range 0-2). This difference was also significant
(t=5.48, df=9, P<0.01; Fig. 2). Horn fly numbers were reduced by 66.7% in the uncov
ered pats compared with those in the covered pats. Combined data from July and Au
gust 1992 showed that the dung arthropod community caused 71.26% mortality to
immature horn flies in artificially formed cattle pats.
The estimates of mortality in the field relied on the contrast between numbers of
flies trapped in artificial pats that were (a) covered immediately with cone traps, and
(b) left uncovered until just before adult flies began to emerge. Mortality was under
estimated to the extent that some predatory or parasitic insects were not excluded by
the cone traps. Damaged adult horn flies were observed in the vial at the top of some
cone traps in both treatments, giving evidence that Solenopsis invicta Buren, red im


Covered Uncovered


Fig. 2. Horn flies (avg.SE) emerged from covered and uncovered cattle pats in a
north-central Florida pasture in 1992 (n=10 for each treatment). Different letters
above bars indicate significant differences within each trial (P<0.05).


December, 1996

















Hu & Frank: Effect ofArthropod Community on Horn Flies 501

ported fire ant (RIFA), succeeded in tunneling underground to reach the cone traps.
A study in the same pasture, but using different methods, showed that RIFA caused
an average of 78.6% mortality to immature horn fly when it was deliberately allowed
access to dung pats (Hu & Frank 1996). Faced with the evidence, we treated the data
as if S. invicta was not excluded by the cone traps.
Horn fly survivorship in our laboratory was about 29.8% without predators, para
sitoids and competitors. Unknown causes of death may have included genetic degra
dation of the laboratory colony (Barlett 1984), desiccation of eggs, inability of some
neonate larvae to enter dung pats, and physiological death (Thomas & Morgan 1972).
High daytime temperatures in the field may have further increased mortality. The
combined effects of these causes and predation by RIFA reduced horn fly numbers
from 100 eggs to an average of 2.95 emerged adults per covered dung pat. In the pats
that were left uncovered to allow access by other components of the fauna, the number
of adults that emerged per pat was reduced to an average of 0.85, a reduction of 71.3%
compared with covered in the field.
Another set of experiments in the same pasture, but not at the same time, used
other methods to exclude RIFA (Hu & Frank 1996). The combined effects of mortality
due to unknown causes and mortality caused by other components of the fauna re
duced horn fly numbers from 100 eggs to an average of 2.42 adults emerged per pat.
In the pats to which RIFA was allowed access, the number of adults that emerged per
pat was reduced to an average of 0.59, a reduction of 78.6% (Hu & Frank 1996).
Although RIFA reduced numbers of several members of the dung fauna, including
some predatory beetles (Hu 1995), its combined effects on horn flies were additional
to the effects of other components of the fauna. Even when constrained by the pres
ence of the other mortality components, RIFA exerted 78.6% mortality, and the other
natural enemies likewise exerted 71.3%. A minimal estimate of their combined effect
is 93.9%, calculated as 100 (100x(1-0.713)x(1-0.786); the actual level of fauna-caused
horn fly mortality may have been considerably higher. Contributions of the arthropod
community in pastures to horn fly mortality in Texas were reported as 87.9% (Roth
1989) and 90% (Kunz et al. 1972), in Missouri 97.7%(Thomas & Morgan 1972), and in
Australia 79-84% (Fay et al. 1990). The mortality of immature horn flies caused by the
dung fauna in the present study was within the range of mortalities reported else
where.


ACKNOWLEDGMENTS

We thank J. F Butler, Entomology & Nematology Dept., University of Florida, for
providing access to his horn fly colony, P. Dixon, IFAS Beef Research Unit, University
of Florida, for use of IFAS beef pastures for this study, C. Geden and J. Hogsette for
review of this manuscript. Yasmin Cardoza kindly translated the abstract into Span
ish. This is Florida Experiment Station Journal Series No. R-05167.


REFERENCES CITED

BARLETT, A. C. 1984. Genetic changes during insect domestication, p. 2-8 in E. G. King
and N. C. Leppla [eds.] Advances and Challenges in Insect Rearing. U.S. Dept.
Agric., Agric. Res. Serv.
BLUME, R. R. 1970. Insects associated with bovine droppings in Kerr and Bexar Coun-
ties, Texas. J. Econ. Entomol. 63: 1023-1024.
BRUCE, W G. 1964. The history and biology of the horn fly, Haematobia irritans (Lin
naeus); with comments on control. North Carolina Agric. Exp. Tech. Bull. 157:
1-33.

















Florida Entomologist 79(4)


BUTLER, J. F, R. L. ESCHER, AND J. A. HOGSETTE. 1981. Natural parasite levels in
house flies, stable flies, and horn flies in Florida, p. 61-79 in R. S. Patterson
[ed.]: Status of Biological Control of Filth Flies. Proceedings of a Workshop. U.S.
Dept. Agric. Sci. Education Administ. Gainesville, Florida.
ESCHER, R. L. 1977. Pupal parasites of the horn fly, Haematobia irritans (L.) (Diptera:
Muscidae) in north-central Florida. Thesis, Department of Entomology and
Nematology, University of Florida, Gainesville, 88 p.
FAY, H. A. C. 1986. Fauna-induced mortality in Haematobia thirouxi potans (Bezzi)
(Diptera: Muscidae) in buffalo dung in relation to soil and vegetation type, p.
142-149 in R. S. Patterson and D. A. Rutz [eds]: Biological Control of Muscoid
Flies. Entomol. Soc. America Misc. Publ. 61.
FAY, H. A. C., A. MACQUEEN, AND B. M. DOUBE. 1990. Impact of fauna on mortality and
size of Haematobia spp. (Diptera: Muscidae) in natural dung pads in Australia
and South Africa. Bull. Entomol. Res. 80: 385-392.
FINCHER, G. T 1992. Injectable ivermectin for cattle: Effects on some dung inhabiting
insects. Environ. Entomol. 21: 871-876.
GREER, N. I. 1975. Effect of insect growth regulations on the bionomics and control of
the horn fly, Haematobia irritans (L.). Ph. D. dissertation, University of Flor
ida, Gainesville, 103 p.
HOGSETTE, J. A., AND P. G. KOEHLER 1986. Biology and control of horn flies, house flies
and stable flies on cattle in Florida. Livestock Production Pointers, University
of Florida-IFAS. 18: 1-11.
HU, G. Y. 1995. The arthropod community in pastures and its biocontrol potential for
the horn fly, Haematobia irritans (L.) in north-central Florida. Ph. D. disserta
tion, University of Florida, Gainesville, 170 p.
HU, G. Y., AND J. H. FRANK. 1996. Effect of the red imported fire ant (Hymenoptera:
Formicidae) on the horn fly and other dung-inhabiting arthropods in north cen
tral Florida. Environ. Entomol. (in press).
KUNZ, S. E., K. D. MURRELL, G. LAMBERT, L. F JAMES, AND C. E. TERRILL. 1991. Esti
mated losses of livestock to pests, p. 69-98 in D. Pimentel [ed.]: CRC Handbook
of Pest Management in Agriculture. Vol. 1, CRC, Boca Raton, Florida.
KUNZ, S. E., B. F HOGAN, R. R. BLUME, AND J.L. ESCHLE. 1972. Some bionomical as
pects of horn fly populations in central Texas. Environ. Entomol. 1: 565-568.
MACQUEEN, A., AND B. P. BEIRNE. 1975. Influence of other insects on production of
horn fly, Haematobia irritans (Diptera: Muscidae), from cattle dung in south
central British Columbia. Canadian Entomol. 107: 1255-1264.
MADSEN, M., B. OVERGAARD NIELSEN, P. HOLTER, O. C. PEDERSEN, J. BROCHNER JES
PERSON, K. M. VAGN JENSEN, P. NANSEN, AND J. GRONVOLD. 1990. Treating cat
tle with ivermectin: Effects on fauna and decomposition of dung pats. J. Appl.
Ecol. 27: 1-15.
MARKS, R. G. 1990. Analyzing Research Data. Robert E. Krieger Publ. Co., Malabar,
Florida.
MORGAN, C. E., AND G. D. THOMAS. 1974. Annotated bibliography of the horn fly, Hae
matobia irritans (L.), including references on the buffalo fly, H. exigua (de
Meijere), and other species belonging to the genus Haematobia. US. Dept. Ag
ric. Misc. Pub. 1278, 134 p.
MORGAN, C. E., AND G. D. THOMAS. 1977. Supplement I: Annotated bibliography of the
horn fly, Haematobia irritans (L.), including reference in the buffalo fly, H. ex
igua (de I. y. I. I and other species belonging to the genus Haematobia, U.S.
Dept. Agric. Misc. Publ. 1278, 38 p.
OKINE, J. S., AND J. F BUTLER 1995. Effect of bovine blood plasma and erythrocyte di
ets on adult horn fly, Haematobia irritans (L.) (Diptera: Muscidae) mortality
and oogenesis. J. Agric. Entomol. 12: 111-117.
ROTH, J. P. 1989. Field mortality of the horn fly on unimproved central Texas pasture.
Environ. Entomol. 18: 98-102.
SHEPPARD, D. C. 1990. Insecticide resistance in horn flies in USA. p. 1216-1222 in
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SIGMAPLOT. 1994. User's Manual: SigmaPlot Scientific Graphing Software for Win
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SKIDMORE, P. 1991. Insects of the British cow-dung community. Field Studies Council,
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THOMAS, G. D., AND C. E. MORGAN. 1972. Field-mortality studies of the immature
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WALL, R., AND L. STRONG. 1987. Environmental consequences of treating cattle with
the antiparasitic drug ivermectin. Nature 327: 418-421.

















Okine et al.: Diadegma insulare Viability after Cold Storage 503


LOW TEMPERATURE EFFECT ON VIABILITY OF DIADEGMA
INSULARE (HYMENOPTERA: ICHNEUMONIDAE) PUPAE AND
EFFECT OF THIS PARASITOID ON FEEDING RATE OF
DIAMONDBACK MOTH LARVAE (LEPIDOPTERA:
PLUTELLIDAE)

J. S. OKINE', E. R. MITCHELL AND G. Y. HU'
'Department of Entomology and Nematology, University of Florida
Gainesville, FL 32611

2Center for Medical, Agricultural and Veterinary Entomology
Agricultural Research Service, U.S. Department of Agriculture
Gainesville, FL 32608

ABSTRACT

Laboratory tests with Diadegma insulare (Cresson), a parasitoid of the diamond
back moth (Plutella xylostella (L.)), were conducted to evaluate the viability of cocoons
stored at 4 C for varying lengths of time and also the effects of parasitism by D. insu
lare on the feeding rate of diamondback moth larvae. The percentage of adults emerg
ing from cocoons declined steadily with time spent in storage at 4 C and was
predictable (r =0.9603; Y 98.3-2.06X; P<0.01). No emergence of D. insulare was ob
served after 49 d in storage. There was a significant difference in feeding rate of par
asitized larvae and non-parasitized larvae. Consumption of collard foliage by
parasitized larvae (86.25% of them were parasitized) the first day after stinging was
about the same as for non-parasitized larvae; but the parasitized larvae then became
sluggish and fed very little on days 2-5 when the experiment was terminated.

Key Words: Biological control, parasitoid, parasitism, Brassica oleracea, Conura side

RESUME

Fueron conducidos ensayos de laboratorio con Diadegma insulare (Cersson), un
parasitoide de Plutella xylostella (L.). Se evalu6 la viabilidad de los capullos almace
nados a 4 C durante diferente tiempo y los efectos del parasitismo por D. insulare en
la tasa de alimentaci6n de las larvas de P xylostella. El porcentaje de adults emergi
dos de capullos decline establemente con el tiempo de almacenaje a 4 C y fue prede
cible (r =0.9603; Y 98.3 2.06X; p<0.01). No fue observada emergencia de D. insulare

















Florida Entomologist 79(4)


despues de 49 dias de almacenaje. Hubo diferencia significativa en la tasa de alimen
taci6n de las larvas parasitadas y no parasitadas. El consume de follaje de acelga por
las larvas parasitadas (86.25% de ellas fueron parasitadas) el primer dia despues de
ser picadas fue casi el mismo que el de las larvas no parasitadas, pero las larvas pa
asitadas se volvieron lentas y se alimentaron muy poco en los dias 4-5 cuando el ex
perimento estaba terminando.





The diamondback moth, Plutella xylostella (L.), is the most important pest of cab
bage and other cruciferous crops worldwide (Muckenfuss et al. 1990). Because the lar
vae attack crops from seedling to harvest stage, virtually all cabbage crops are treated
with insecticides during the growing season. Larval control with chemical pesticides
started failing in the 1980s and insecticide resistance has since spread to Bacillus
thuringiensis spp. kurstaki Berliner (McLaughlin & Mitchell. 1993, Tabashnik et al.
1990, Shelton & Wyman 1992). Coupled with resistance, the increasing cost of pesti
cides and environmental awareness has encouraged the search for alternative man
agement strategies (Ooi & Sudderuddin 1978).
Integrated pest management provides the most viable alternative to the heavy re
liance on pesticides. An integrated approach to control lepidopterous pests in cabbage
using multiple tactics is described by Biever et al. 1994. The system has had some suc
cess in the Rio Grande Valley of Texas and in Central America. For diamondback
moth control, this involves scouting, limiting the use of conventional pesticides, more
reliance on B. thuringiensis-based insecticides, and parasitoids. Of the parasitoids at
tacking the diamondback moth, C. plutellae Kurdjumov, Diadegma insulare (Cresson)
and D. semiclausum (Hellen) show the most promise (Ooi & Lim 1989, Ooi 1990,
Tabashnik et al. 1990).
D. insulare is the most important parasitoid of diamondback moth in North Amer
ica (Latheef & Irwin 1983, Pimentel 1961, Oatman & Platner 1969, Harcourt 1960,
1963, 1986, Losata & Kok 1986, Horn 1987), with parasitism rates of >90% reported
in untreated fields (Muckenfuss et al 1990). To integrate D. insulare into diamond
back moth management systems, more information is needed on its biology, ecology
and effect on diamondback moth.
The purpose of this study was to evaluate the survival of field-collected D. insulare
pupae stored at a low temperature (4'C) for varying lengths of time, and the effect of
D. insulare parasitism on feeding by host larvae.


MATERIALS AND METHODS

Viability of D. insulare Pupae Stored at Low Temperature

Pupae of D. insulare were collected from collard plants (Brassica oleracea var.
acephala L.) serving as a trap crop between 2 commercial fields of cabbage (Brassica
oleracea var. capitata) in Bunnell, Florida in mid-May 1995 (E. R. Mitchell et al., un
published data). No attempt was made to cold-adapt parasitoids before use in exper
iments. High D. insulare parasitism levels were recorded for diamondback larvae on
the collards during the growing season.
For the study, collard plants were uprooted, bagged, and transported to the labor
tory where D. insulare cocoons were collected. The cocoons were inspected carefully to
exclude empty cocoon cases, held in 250-ml waxed paper DixieTM cups with ventilated
lids and stored in a Nor lakeTM walk-in environmental chamber maintained at 4C and


December, 1996

















Okine et al.: Diadegma insulare Viability after Cold Storage 505

70+10% RH with continuous fluorescent lighting. For 7 consecutive wk after the co
coons were collected, varying numbers were removed from cold storage and put into
fresh Dixie'T cups with ventilated lids. The cups were then set up in the laboratory un
der ambient conditions of 252C, 70-80% RH and under continuous fluorescent light.
A water-soaked cotton ball and light smears of honey on the inside of the cup served as
water and food sources for emerging parasitoids. Adult emergence was checked daily
by opening the cups in a screened cage. Emerged adults were aspirated and sexed. A
control group from the same initial collection of pupae not subjected to cold storage also
was set up under ambient laboratory conditions and followed for emergence.
Adult emergence was recorded for 25 d after initial set up of each batch of pupae.
Unemerged cocoons were examined for evidence of parasitism using a dissecting mi
croscope. Conura (Spilochalcis) side (Walker) (Hymenoptera: Chalcidae) and dipteran
parasitoids emerged from some of the cocoons. Their numbers are recorded but not
used in the calculation of the percent emergence. Regression analysis was performed
(y percent emergence; x=days in storage) using Sigma Plot' (ver. 3.0, Jandel Corp.,
San Rafel, CA).

Effect of D. insulare Parasitism on Feeding Rate of Diamondback Moth

Diamondback moth eggs were obtained by exposing collard plant leaves in a
screened cage containing several hundred moth adults for 24 h. The leaves with eggs
were transferred into DixieTM cups with ventilated lids. Young collard leaves from collard
plants uprooted from the field and stored at 4 C were added, and the eggs were held un
til hatch for 3 d under ambient laboratory conditions of 252 C, 70-80% RH and contain
uous fluorescent light. Two days after hatch, 20 second instar larvae were carefully
picked with flexible forceps and put into each of 8 DixieTM cups with ventilated covers.
One group of 4 cups was used as the treatment parasitismm), and the other half
served as the control. Young collard leaves were introduced into each cup. Five 4-d-old
mated female D. insulare from field-collected cocoons were released by aspirator into
the treatment cups through a hole on the side that was then plugged with cotton. The
larvae were exposed to attack by the parasitoids for 24 h. Water soaked cotton balls
and smears of honey on the inside of the cups served as water and food sources for the
parasitoids. After 24 h, the parasitoids were released by opening the cups in screened
cages. Old collard leaves were removed and replaced with fresh ones. The larvae cling
ing to the old leaves were brushed gently onto the fresh leaves. The cups were held in
the laboratory under ambient conditions as described previously. Collard leaves were
replaced daily to provide an adequate supply of leaf material for the developing lar
vae. Leaf consumption rate for each replicate was determined by measuring con
sumed areas of the leaves with a mm2 plastic grid under a dissecting microscope. No
attempt was made to correct for leaf shrinkage or expansion. Observations were made
daily until no feeding was observed or until pupation of either diamondback moth or
D. insulae larvae. Percent parasitism, mean feeding rate per replicate per day, and
percent mortality were calculated at the end of the trial. Experimental and control
group results were compared by analysis of variance (ANOVA) and the means were
separated using the Ryan-Einot Gabriel-Welsch multiple range test (REGWQ)
(P 0.05; SAS Institute, 1988).

RESULTS AND DISCUSSION

Results of the pupal viability test indicated that adult emergence decreased with
long term storage at 4C (Fig. 1). Percent emergence from the cocoons decreased lin
early with increasing storage time (r2 0.9603; Y 98.3-2.06X; P<0.01). No emergence
















Florida Entomologist 79(4)


100




80 Y=98.3 2.06X
5 R2= 0.96, P < 0.01



60



E
W 40




20




0-


0 10 20 30 40 50

Days in storage at 4C

Fig. 1. Percent emergence of Diadegma insulare adults from cocoons stored at 4C
for varying lengths of time.


of D. insulaewas observed after 49 d in storage. The highest emergence of 82% was ob
trained from cocoons stored for 14 days compared to 92% for cocoons in the control that
were not subjected to cold storage. More males than females (127:71) emerged from
cocoons stored at 4C. However, the sex ratio of 19:1.796 was only slightly higher
than that of the control group which was 1 1: 1.5 6. The sex ratio for parasitoids emerg
ing from cocoons stored at 4C possibly was skewed by the low numbers of individuals
that emerged after extended periods of cold storage. Data from cocoons collected from
the collards in March had a sex ratio of almost 1 : 1 : (Mitchell et al., unpublished
data). The change in sex ratio from March to May suggests that environmental factors
and/or increased population pressure favored a shift in favor of male D. insulare. The
skewed sex ratio favoring males is consistent with those obtained for Fl and subse
quent generations when reared in the laboratory (unpublished data), and it is a sig
nificant factor in attempts to rear the parasitoid in the laboratory for extended
periods.
Conura (Spilochalcis) side (Walker) and a dipteran parasitoid emerged from some
of the cocoons even when the hosts appeared to be no longer viable, indicating that the


December, 1996















Okine et al.: Diadegma insulare Viability after Cold Storage 507

300



250-
a

S200 Unparasitized



S150-

E

c 100- b



50 Parasitized
a
a\
0- 2
0 1 2 3 4 5
Days after parasitism
Fig. 2. II, i I.. I..,: rate of diamondback moth larvae parasitized by Diadegma in-
sulare. Means on the same day with different letters are significantly different (Ryan
Einot Gabriel-Welsch multiple range test).

parasitoids perhaps were more cold tolerant than D. insulare. Dissections of une
merged cocoons showed dead pharate D. insulare adults. The inability of fully formed
adults to emerge from their cocoons may be attributed to a lowering of the metabolic
rate when exposed to 4C which resulted in reduced I II II.1. .. i : to break through
the cocoon. Because D. insulare overwinters as a pupa (Harcourt 1960), information
obtained could be important in providing insight about the fate of cocoons released
during cold spells in the field. The length of time at which viability is maintained also
is important with respect to storage of cocoons for use in experiments during periods
when D. insulare are not readily available in the field.
Figure 2 depicts the effect of D. insulare parasitism on feeding rate of diamond
back larvae. There was a significant difference in the foliage consumption rate be
tween parasitized and non-parasitized larvae during the period of the experiment
(F-143.97; df=30; df=39; P<0.05). The multiple range test showed no significant dif
ference in foliage consumption between the parasitized and unparasitized larvae one
day after parasitism. The parasitized larvae then became sluggish and fed very little.
There were significant differences in feeding rate between the two groups on days 2

















Florida Entomologist 79(4)


through 4. There was no significant difference on day 5 because most of the larvae or
parasitoids had pupated. Idris & Grafius (1993b) also reported less feeding by para
sitized larvae compared with non-parasitized ones. Parasitism was 85.25%, which
was less than the 93% observed by Goodwin (1979) in field settings for other species
of Diadegma and the 95% reported by Muckenfuss et al. (1990) for D. insulare.
In the control group, leaf consumption was high for 3 days after set-up and then
dropped dramatically. This was attributed to the insects' preparation for pupation. No
mortality was recorded in the control group.
Because development of D. insulare is highly synchronized with diamondback
moth development and the parasitoid has excellent searching ability (Idris & Grafius
1993a), it is a good candidate for use in IPM programs for control of diamondback
moth in cabbage. The information reported here will be useful in developing state
gies for managing natural populations of D. insulare using various tactics including
trap crops, mating disruption (McLaughin et al. 1994) and pesticides with low envi
ronmental impact such as Bacillus thuringiensis-based products (Biever et al. 1994).


ACKNOWLEDGMENTS

We appreciate the assistance of W Copeland, N. Doran, R. Furlong, J. Gillett, J.
Leach, E. Lanehart, and J. Rye (IABBBRL, USDA-ARS, Gainesville, FL) in planting
and harvesting the collards and collecting cocoons; of G. S. Evans (Department of En
tomology/Nematology, University of Florida, Gainesville) for identifying parasitoids;
and of R. Hawkins, T Turner, R. Mitchell, and Q. Emery (Flagler County, FL.) for the
use of their cabbage crop and land.
This article reports the results of research only. Mention of a proprietary product
does not constitute an endorsement or the recommendation for its use by USDA.


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BIEVER, K. D., D. L. HOSTETTER, AND J. R. KERN. 1994. Evolution and implementation
of a biological control-IPM system for crucifers: 24-year case history. American
Entomol. 40: 103-108.
GOODWIN, S. 1979. Changes in numbers in the parasitoid complex associated with the
diamondback moth Plutella xylostella (L.) (Lepidoptera) in Victoria. Australian
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HARCOURT, D. G. 1960. Biology of the diamondback moth, Plutella maculipennis
(Curt) (Lepidoptera: Plutellidae) in eastern Ontario III. Natural enemies. Ca
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HARCOURT, D. G. 1963. Major mortality factors in population dynamics of the dia
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nadian Entomol. Soc. Mem. 32: 55-66.
HARCOURT, D. G. 1986. Population dynamics of the diamondback moth in southern
Ontario, pp. 1-15 in N. S. Talekar and T D. Griggs [eds.], Diamondback moth
management. Proc. 1st Inter. Workshop at Asian Veg. Res. and Dev. Center, 11
15 March 1985, Shanhua, Taiwan.
HORN, D. J. 1987. Vegetational background and parasitism of larval diamondback
moth on collards. Entomol. Exp. Appl. 43: 300-303.
IDRIS, A. B., AND E. GRAFIUS. 1993a. Field studies on the effect of pesticides on the di
amondback moth (Lepidoptera: Plutellidae) and parasitism by Diadegma insu
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IDRIS, A. B., AND E. GRAFIUS. 1993b. Pesticides affect immature stages of Diadegma
insulare (Hymenoptera: Ichneumonidae) and its host, the diamondback moth
(Lepidoptera: Plutellidae). J. Econ. Entomol. 86: 1203-1212.


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LASOTA, J. A., AND L. T. KOK. 1986. Diadegma insularis (=insulare) (Hymenoptera:
Ichneumonidae) parasitism of the diamondback moth (Lepidoptera: Plutel
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LATHEEF, M. A., AND R. D. IRWIN. 1983. Seasonal abundance and parasitism of lepi
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MCLAUGHLIN, J. R., AND E. R. MITCHELL. 1993. Integration of mating disruption to
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pheromones and other semiochemicals in integrated control-Pheromone tech
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Inst., Chatham, England.
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mondback moth (Lepidoptera: Plutellidae) in cabbage: Reduction of mating
and suppression of larval populations. J. Econ. Entomol. 8: 1198-1204.
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Florida Entomologist 79(4)


IMPACT OF THE MIRID BUG CAPSODES INFUSCATUS
(HEMIPTERA: MIRIDAE) ON FRUIT PRODUCTION OF THE
GEOPHYTE ASPHODELUS AESTIVUS: THE EFFECT OF
PLANT DENSITY

IDO IZHAKI', NOA MAESTRO, DALIT MEIR AND MEIR BROZA
Department of Biology, University of Haifa at Oranim, 36006 Tivon, Israel

'Present address: Dept. of Zoology, 223 Bartram Hall, Univ. of Florida
Gainesville, FL 32611, USA

ABSTRACT

The leaf, stalk, flower, and fruit of the geophyte Asphodelus aestivus Brot. (Lili
aceae) in east Mediterranean mesic habitats are mainly attacked by the monopha
gous mirid bug Capsodes infuscatus Brulle (Hemiptera: Miridae). The sexual
reproductive performance of A. aestivus was examined under natural levels of insect
herbivory at three different host densities at the same site. Plants in the low and me
dium density plots were heavily attacked by C. infuscatus and failed to produce fruits,
while plants from high density plots were less intensively attacked and produced
some fruits. The observed inversely density-dependent damages are discussed with
respect to plant compensation, population dynamics, and sexual vs. asexual reproduc
tion.

Key Words: Insect herbivory, plant density, mirid bug, fruit production, geophyte, Is
rael

RESUME

La hoja, el tallo, la flor y el fruto de Asphodelus aestivus Brot. (Liliaceae) en el Me
diterraneo Oriental son atacadas por el mirido mondfago Capsodes infuscatus Burlle
(Hemiptera: Miridae). La capacidad sexual reproductive de A. aestivus fue examinada
bajo niveles naturales de herbivoria por insects a tres densidades diferentes de hos
pedante en el mismo lugar. Las plants en las parcelas con densidades baja y media
fueron fuenrtemente atacadas por C. infuscatus y no produjeron frutos, mientras que
las plants de parcelas con alta densidad fueron menos intensamente atacadas y pro
dujeron algunos frutos. Los danos densodependientes observados son discutidos con
respect a la compensacidn de las plants, dinamica de poblacidn y reproducidn sexual
vs. asexual.





Crawley (1989) claimed that plants have more impact on the population dynamics
of insects than insects have on the population dynamics of plants. In general, monoph
agous insects tend to have little impact on equilibrium plant abundance even when
the insects are food-limited (Crawley 1983). However, several studies have suggested
that herbivorous insects have a great impact on the evolution and population dynam
ics of plants (Blais 1983, Stalter & Serrao 1983, Twery & Patterson 1984, Berryman
et al. 1985). In this case, herbivorous insects may reduce the reproductive success of
their host-plants either by direct predation on flowers (e.g. Louda 1982, Hendrix &
Trapp 1989) and seeds (e.g. Louda 1982) or indirectly by feeding on other plant parts
such as foliage (e.g. Rausher & Feeny 1980) and roots (e.g. Gange & Brown 1989).


December, 1996

















Izhaki et al.: Mirid-Bug Herbivory and Fruit Production 511

This study deals with the effects of a monophagous insect on the sexual reproduc
tive success of its geophyte host in Mediterranean habitats. The female mirid bug,
Capsodes infuscatus Brulle (Hemiptera: miridae), deposits eggs inside the inflores
cence stalk of its host (Asphodelus aestivus Brot. = A. microcarpus Salzm. = A. ramo
sus Viv.) in spring. Developing nymphs as well as adults feed on this plant. Different
structures of A. aestivus are consumed by the bugs including leaves, flower stalks,
buds, flowers and fruits (Ayal & Izhaki 1993). C. infuscatus nymph feeding may kill
young inflorescences, or suppress the development of the inflorescence branches and
kill all its flowers while adult feeding may also kill green fruits (Ayal 1994). The geo
phytes also reproduce vegetatively and are distributed in clones (for more detailed de
scription of plant phenology see Schuster et al. 1993, and for the life cycle of the bug
see Ayal & Izhaki 1993).
Several authors reported that high-density host plants are subjected to greater
herbivore attack than low-density plants (Dethier 1959; Orians et al. 1975). Under
such circumstances, the herbivorous insect may regulate plant density. Other studies,
however, point out that isolated plants have been attacked by more herbivorous in
sects than high-density stands (Pimental 1961, Heathcote 1969, Jones 1977). If this
is true, insect attack may act to promote a local increase in plant density rather than
to limit it (Rausher & Feeny 1980). In some cases there was no evidence to different
ate the degree of damage on the reproductive success between plants growing in high
and low-densities (e.g., Rausher & Feeny 1980).
The goals of this study were to: (a) estimate the damage to fruit production of the
host-plant clones caused by C. infuscatus in its natural habitat, and (b) detect corre
nations between the clone density and the reduction in its reproductive success due to
C. infuscatus feeding.

MATERIALS AND METHODS


Study Area

The study was conducted at the western end of Yizrael valley, 1 km south of Kiryat
Tivon, Israel (32 42'N, 35 07'E, 100 m altitude). The annual mean temperature is
20 C, and the mean relative humidity is 75%. The mean annual precipitation is 600
mm, and there are 240 dew days per year (Atlas of Israel 1985). The 5000 m2 study
area was intensively grazed by sheep and goats before and during the study. However,
these herbivorous domestic mammals did not consume Asphodelus aestivus, probably
due to high amounts of secondary compounds in its tissues (Zohary 1962). Therefore,
A. aestivus is common and locally dominant in large areas in the Mediterranean re
gion which are now, and have been overgrazed for a long time (Schuster et al. 1993).
The study began in December before the first nymph emerged and continued until the
end of the fruiting season (March).


Study Plots

The study area was covered by several patches of A. aestivus clones at different
densities which were sampled along randomly-chosen transects. A total of 6 samples
were taken at 30 m intervals along each of 5 transects. Each sample unit was 4 x 4 m.
Clone density within the samples was categorized as: (a) low (< 1 clone per m2), (b) me
dium (1-3 clones per m2) and (c) high (>3 clones per m2). We sampled until each of the
above density categories was represented twice in each transect. Thus, 30 plots were
established, 10 for each clone density. Each clone and inflorescence stalk in each plot

















Florida Entomologist 79(4)


were marked and numbered. The diameter of each clone was measured at the begin
ning of the study and the surface area of each clone was calculated. The phenological
status of A. aestivus, insect density, and damage were observed twice a month as de
scribed below.


Bug Density

When only a few bugs were present (< 10 per plant), they were visually counted on
the plant. When a large number of bugs were present, a 50 x 30 cm plastic tray was
placed beneath each clone and the observer hit the clones until the bugs fell into the
tray where they were counted. The bugs were relocated on the same clone immedi
ately after counting. The average number of bugs per clone per plot was calculated
and compared within each sample date among the three clone densities using one-way
ANOVA followed by Duncan's Multiple Range Test (P<0.05, SAS 1988).


Damage Estimation

Leaves and flowers. Damage to A. aestivus leaves was recorded for each clone and
was classified into four categories: 0-no damage, 1 scattered yellow spots on the leaf
area due to bug feeding, 2-the leaf end had turned yellow due to bug feeding, and 3
most of the leaf area had turned yellow due to bug feeding. The average damage cat
egory was calculated for each plot, for each date and was compared among the three
densities by Kruskal-Wallis one-way ANOVA (SAS 1988).
During flowering, the number of A. aestivus inflorescences with flowers were
counted and their proportion among all inflorescences in each plot was calculated. The
mean proportion of flowering inflorescences was compared between the three densi
ties by one-way ANOVA after arcsin square root transformation.
Fruits. Several A. aestivus clones without damage were randomly sampled at the
end of the fruiting season for the number of fruits and the inflorescence stalk diam 5
cm above the ground. We assumed that the lack of attack in these plants did not rep
resent differences in reproductive effort. On the basis of the correlation between stem
diam and fruit production in these clones, a regression equation was established to
predict the potential fruit production from the stalk diam. The diam of the inflores
cence stalk from damaged plants in the study plots was recorded and the expected
fruit production was calculated from this equation and compared to actual fruit pro
duction (Ayal & Izhaki 1993). Because fruit production in low and medium density
plots was zero, this procedure was carried out for high clone density plots only. The dif
ference between observed and predicted fruit production was used as an estimate of
insect damage.


RESULTS


Clone Density

The average number of A. aestivus clones per plot was significantly different be
tween the three defined densities with 3.2 at low density plots, 20.8 at medium den
sity and 73.6 at high density The size of the clone in terms of the surface area it
occupied on the ground, and the number of inflorescences per clone were independent
of clone density (Table 1). However, the density of inflorescences at the high density
plots was 15 and 3 times more than at the low and medium density plots, respectively.


December, 1996


















Izhaki et al.: Mirid-Bug Herbivory and Fruit Production 513

TABLE 1. COMPARISON OF PLANT AND INFLORESCENCE DENSITY, FLOWERING, AND
FRUIT PRODUCTION OF A. AESTIVUS IN THREE DIFFERENT CLONE DENSITIES.
ALL RATIOS WERE ARCSIN SQUARE ROOT TRANSFORMED BEFORE STATISTICAL
ANALYSIS.

Plant Density
Mean+SE'

Low Medium High
n=10 n 10 n 10 df F2

Number of clones 0.2+0.03' 1.3+0.12b 4.60.31' 2,26 228.6***
per m2
The area of clone
(cm2) 1594+239' 1082+125' 1493+196' 2,24 2.03 ns
Number of
inflorescences
per clone 4.0+0.8' 3.1+0.1' 2.90.6' 2,24 0.77 ns
Number of
inflorescences
per m2 0.8+0.2' 3.7+0.4b 12.12.1' 2,24 60.87***
Proportion of
inflorescences
with mature
flowers 0.13+0.09b 0.01+0.01b 0.220.06' 2,24 5.85**
Number of fruits 0" 0" 5.4+4.6" 2,26 2.11 ns
per clone

'Means followed by same letter in rows are not significantly different as determined by Duncan's Multiple
Range Test (P<0.05).
2**0.01

Bug Density

The number of C. infuscatus nymphs per clone was greater in the low A. aestivus
density plots than in the high density plots during two sample dates (Fig. 1). During
the first three observations, there were no differences between the number of nymphs
per clone among the low and medium densities. However, at the end of January and
at the beginning of February, when peak C. infuscatus infestation occurred, the num
ber of nymphs in the low density plots was much higher than in the medium density
plots. At the end of the study, no differences could be detected between the number of
nymphs among the three densities.


Infestation Level

The majority of the clones in low density plots were already infested at the begin
ning of the season, reaching 100% infestation from mid-January (Fig. 2). Although the
mean proportion of infested clones in medium density plots was lower than in the low
density clones, the differences were insignificant. The proportion of infested clones in
high density plots was much lower (<40%) throughout most of the study. The proper
tion of infested clones in the high density plots decreased during the first half of the
study (until January 29) but increased later on.

















Florida Entomologist 79(4)


125
C BA

100 -
U

a 75

CBA
S 50- BAB A BAA BAA


S25


0
12/22 1/8 1/16 1/29 2/9 2/19 3/1
DATE

HIGH M IvEDIUM I i I LOW
DENSITY DENSITY DENSITY

Fig. 1. Densities+SE of C. infuscatus on A. aestivus clones at three different clone
densities. Differences in densities were analyzed using one-way ANOVA. Different
letters above bars indicate significant difference as determined by Duncan's Multiple
Range Test (P<0.05).

Damage to Foliage

The mean damage rank to A. aestivus leaves increased throughout the study in the
low and medium clone densities, while in the high density plots, it increased only in
the second half of the study period (from February 9, Fig. 3). Leaf damage in low and
medium density plots was similar and much higher than in the high density plots.
There was a positive correlation between the damage rank and the number of bugs
per clone when pooling the data from the three densities in different dates (r=0.62,
P<0.001,n=155).

Damage to Flowers and Fruits

Only 1% of A. aestivus inflorescences at medium density and 13% at low density
produced flowers, but these two values were not significantly different (Table 1). In
contrast, the mean proportion of inflorescences in high density plots which produced
flowers (22%) was significantly higher than the other plots. Total failure in fruit pro
duction was observed in the low and medium density plots. However, the very low and
varied fruit production (Coefficient of variation=254%) detected in the high density
plots was not significantly different than in the other two densities.
Two linear equations were calculated to predict the number of fruits as a function
of inflorescence stalk diam in (a) uninfested clones; and (b) damaged clones in the high
density plots (Fig. 4). The actual fruit production of the damaged plants was much
lower than that of the uninfested clones. The significant differences between these
two equations (t=3.72, d.f. 125, P<0.001) presumably represents the actual damage
in fruit production to plants in the high density plots. Therefore, the actual damage


December, 1996

















Izhaki et al.: MiridBug Herbivory and Fruit Production 515


1.20
12 BAA CBA BAA BAA BAA
o 1.00 .. ..


0.80

0.60


0.40


020 /
0 t 00

12/22 1/8 1/16 1/29 2/9 2/19
DATE

S HIGH MEDIUM I I LOW
DENSITY DENSITY DENSITY

Fig. 2. Proportions of clones+SE of A. aestivus infested by C. infuscatus at three dif
ferent clone densities. Differences in arcsin square root transformed proportions were
analyzed using one-way ANOVA. Different letters above bars indicate significant dif
ference as determined by Duncan Multiple Range Test (P<0.05). The proportion of in
fested clones in medium density was not measured in 2/19.


in terms of number of fruits per stalk (Y) was also a linear function of stalk diam (X):
Y 11.63X+16.65.

DISCUSSION

Inverse Density Dependent Damage

The colonization behavior of an herbivore is determined by the spatial and tempo
ral availability of its host plants and the dispersion, behavior and abundance of its en
emies and competitors (Cromartie 1975). The proportion of infested A. aestivus clones
at the beginning of the season, before C. infuscatus nymphs had the ability to move
between clones (personal observation), was much higher in low and medium than in
high density plots. Therefore, adult females at the end of the previous year probably
deposited eggs in inflorescences of clones at low density but only in 40% of the clones
at high density. The proportion of infested clones in high density plots increased
throughout the second half of the season, when the nymphs became more mobile, but
remained high at the plots of low and medium densities throughout the season.
Several studies have demonstrated that hosts of several neotropical Euptychiine
butterflies (Nymphalidae: Satyrinae) are more likely to bear eggs or larvae if they are
scarce and isolated than if they are clumped and abundant (Mackay & Singer 1982
and reference therein). Flower attack rates can also be inversely density dependent
(De Steven 1983, Crawley & Pattrasudhi 1988). These similar observations could
arise from several causes such as different plant quality (size, chemistry, etc.) among

















Florida Entomologist 79(4)


3.50

y 3.00 ** - * -* *-* -*** *x

S 2.50

I 2.00

S 1.50

4 1.00 .

0.50 -

0.00
12/22 1/8 1/16 1/29 2/9 2/19 3/1
DATE

S HIGH EDIUM I I LOW
DENSITY DENSITY DENSITY

Fig. 3. Foliage damage rankSE of A. aestivus caused by C. infuscatus in three dif
ferent clone densities. Differences in damage ranks were analyzed by Kruskal-Wallis
One-way ANOVA. Significance is indicated on each date by: *P<0.05, **P<0.01,
***P<0.001.


densities or an active preference of insects for isolated clones. But, host plant search
by herbivorous insects may be initiated at random, or at least without reference to lo
cal plant density. If this is the case, each plant is at high risk when an insect starts
searching in an area of low density. Thus, the high risk of isolated plants may be a side
effect of the random initiation of search, rather than the result of active preference on
the part of the insect (Mackay & Singer 1982, Thomas 1989). Whatever the primer of
insect behavior, A. aestivus plants at relatively low density were at high risk to be col
onized by C. infuscatus while over 60% of the clones at high density escaped bug col
onization.

Damage to Sexual Reproduction

This study also revealed that A. aestivus plants at low and medium densities could
not produce fruits, presumably due to intensive bug herbivory This failure in fruit
production contrasted the success of several clones in high density plots that did pro
duce fruits. Hence, mirid bugs may act as selective agents favoring sexual reproduc
tion if members of A. aestivus clumps are more prolific sexually than isolated clones.
Herbivory by other monophagous insects on different perennials were also found
to reduce the number and size of seeds produced (Louda 1982, Waloff & Richards
1977). It was also demonstrated that feeding on buds and flowers by mirid bugs can
cause a heavy loss of fruit production in sainfoin (Onobrychis viciifolia, Morrill et al.
1984). Mirids feeding on the flower stalks of grasses can cause silver top in which an
entire panicle of unfilled seeds is produced as a result of a blockage of the phloem
(Wagner & Ehrhardt 1961).
Direct attack on ripening fruits by adult mirid bugs (Lygus borealis and Adelpho
coris lineolatus, Hemiptera: Miridae) causes a more or less linear decline in seed pro


December, 1996

















Izhaki et al.: Mirid-Bug Herbivory and Fruit Production


300


240


180 -


120 -


60 F


6 9 11 14

INFLORESCENCE STALK DIAMETER (mm)


* INFESTED
CLONES


o UNINFESTED
CLONES


Fig. 4. Relationships between the number of mature fruits of A. aestivus as a func
tion of the diameter of inflorescence stalks in (a) infested clones in high density plots
(R2 0.21, n 83, P<0.001) and (b) uninfested clones in the study area (R2 0.41, n46,
P<0.001).The difference between these two lines represents the damage caused to
fruit production by C. infuscatus.


duction in sainfoin as the number of insects increases (Morrill et al. 1984). However,
all stages of C. infuscatus feed upon A. aestivus; nymphs consume leaves early in the
season, but as they develop they feed preferably on inflorescence stalks, flowers, and
fruits (Ayal & Izhaki 1993). Therefore, reduced fruit production in this study may be
an indirect result of feeding damage on leaves as well as direct damage to flowers and
fruits. A positive correlation between the number of young nymphs of C. infuscatus
per clone early in the season, long before fruit appearance, and the resulting damage
to fruit production in A. aestivus was previously demonstrated in a desert habitat
(Ayal & Izhaki 1993).

Compensation and Reproduction

The relation between timing of insect damage and plant phenological stage is usu
ally critical for understanding compensation responses, at least in annual species
(Trumble et al.1993). However, Capsodes attacks A. aestivus shortly after the first
leaves appear until the above ground parts dry-up. Such continuous pressure can be
extremely detrimental to the plants, as they may not recover reproductive potential
in the same season. However, reallocation of available assimilates from flowers and
fruits to storage in the tuber may result in compensation. This can result in increased
sexual and asexual reproductive efforts in the next growing season or increased life
span of the individual (Hendrix 1988). Therefore, it is suggested that isolated clones
which are heavily attacked by bugs reallocate more reserves to the tuber than high


- 27.88


I


Y = 18.1X 11.23 o 0


o ooo > oo


0 o

Y =o @7

Y = 6.47X

















Florida Entomologist 79(4)


density clones which suffer less massive attack. As growth continues and clones come
to occupy large areas, opportunities for seedling establishment are reduced. This fa
vors further reduction in sexual reproduction as well as increased dispersal and/or
dormancy (Waller 1988). However, this study revealed that the bugs intensively at
tacked isolated plants and reduced their chance to disseminate seeds when the envi
ronmental conditions favored seed establishment. Only later, when the conditions
favored asexual reproduction, did some plants escape the bug's herbivory and have
the potential to reproduce sexually.

Population Dynamics of the Plant

Intense feeding by herbivores can result in a 99% reduction in host plant popular
tion reproduction (Huffaker et al. 1983); however, a selective pressure that reduces
parent fitness by even 1% can be important and result in significant changes in the
host population in just a few generations (Crow & Kimura 1970). Furthermore, pop
ulation dynamics of other plant species have been affected by much lower percent re
ductions in seed yield due to insect damage (e.g., Louda 1982). Although many
examples can be found in which herbivory leads to reduction or even extinction of
plant species, other plants, despite visible impact on primary production, do not seem
less successful than plants with less herbivore damage (Meijden et al. 1988). Because
the activity of C. infuscatus reduces plant growth and seed production, but does not
result in the mortality of the plant, the effects of their feeding may be manifested only
as reductions in the population size of subsequent generations. Therefore, the actual
effects of the mirid bug herbivory on population dynamics can only be assessed prop
erly when studied over several generations. (e.g., Verkaar 1987).

ACKNOWLEDGMENTS

We are grateful to Y. Ayal and three anonymous reviewers for valuable comments
on earlier draft of the manuscript.

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BERRYMAN, A. A., B. DENNIS, K. F. RAFFA, AND N. C. STENSETH. 1985. Evolution of op
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Florida Entomologist 79(4)


DIEL HOST-SEEKING ACTIVITY OF CHRYSOPS CELATUS
(DIPTERA: TABANIDAE) IN NORTHWEST FLORIDA

J. E. CILEK AND E. T. SCHREIBER
John A. Mulrennan, Sr. Arthropod Research Laboratory, Florida A & M University
4000 Frankford Avenue, Panama City, FL

ABSTRACT

Diel host-seeking activity of adult Chrysops celatus Pechuman was studied in
northwestern Florida during June 1993 and 1994. Primary peak activity occurred at
0645 h (CST) with a secondary peak at 1945 h. Host-seeking behavior was correlated
with relative humidity but not temperature and light intensity. No host-seeking ac
tivity was observed at darkness. In all studies, the majority of flies initially marked
and released were not recaptured in the area. Anthrone assays from C. celatus col
elected adjacent to the immediate study area revealed that approximately 96% had fed
on fructose, while parity assays indicated about 92% of host-seeking adults were nul
liparous.

Key Words: Chrysopinae, annoyance, behavior, population ecology

RESUME

Fue estudiada la actividad de bfsqueda de hospedante en adults de Chrysops ce
latus Pechuman en Florida noroccidental durante Junio de 1993 y 1994. La actividad
primanria pico ocurri6 a las 0645 h horaa standard central) con un pico secundario a
las 1945 h. La bfsqueda del hospedante estuvo correlacionada con la humedad rela
tiva pero no con la temperature y la intensidad de luz. No fue observada actividad de
busqueda en la obscuridad. En todos los studios, la mayoria de las moscas inicial
mente marcadas y liberadas no fueron recapturadas en el area. Ensayos con anthrone
en C. celatus colectados junto al area de studio revelaron que aproximadamente el
96% se habia alimentado con fructosa, mientras que ensayos ovoparidad indicaon que
alrededor del 92% de los adults buscando hospedante fueron nuliparos.


Many species of horse flies and deer flies (Diptera: Tabanidae) can be serious eco
nomic and nuisance pests in various portions of the U.S. (Harwood & James 1979). In


December, 1996

















Cilek & Schreiber: Tabanid Host-Seeking Activity


northwest Florida the deer fly, Chrysops celatus Pechuman, can be abundant enough
in residential and recreational areas to be considered a serious biting pest of humans.
This species has been reported to occur during March through November with peak
seasonal abundance from mid-May through June in Florida (Jones & Anthony 1964).
The bite of Chrysops spp. can be painful and has been reported to cause severe reac
tions in some individuals (Mease 1943). Larval control using insecticides has proven
to be difficult because of developmental site patchiness and environmental concern for
the impact insecticides might impose on nontarget organisms in wetland habitats
where most Chrysops species develop (Jones & Anthony 1964). Additionally, the use
of insecticides for area-wide adult tabanid control has met with limited success
(Anderson 1985).
The purpose of this study was to determine the diel host-seeking activity of adult
C celatus so periods for maximum exposure to control procedures against pestiferous
populations could be identified. Additionally, we wanted to be able to recommend pe
riods during the day when persons engaged in outdoor recreation or work-related ac
tivities could avoid these pests.


MATERIALS AND METHODS

The study was conducted on June 11, 12, 1993 and June 3, 6, 8, 11, 12, 1994 in Wal
ton County near Grayton Beach, Florida, USA. Sampling commenced during these
two weeks because it is the usual period that seasonal peak abundance for adult C.
celatus has been observed previously in north Florida (unpublished observation). The
16 ha study area, located adjacent to a black needlerush (Juncus roemerianus
Scheele) marsh on Choctawhatchee Bay, was once a commercial pine bottomland for
est containing slash pine (Pinus elliotiiEx. Chapm.). This forest also contained a mix
ture of magnolia (Magnolia grandiflora L.) and live oak (Quercus virginiana Mill.).
Host-seeking C. celatus were collected using a 32 cm diam aerial insect net. Four
staked 30 m by 4 m wide transects were used: 2 near the edge of a forest along a dirt
road and 2 through the forest canopy Transects were separated by at least 50 m. Each
sample consisted of continually making figure eight sweeps in front of and behind the
head, shoulders, and legs while walking slowly along each transect for 1.5 min. Two
persons simultaneously sampled one inner and outer transect. Sampling was con
ducted so that no one person consecutively sampled the same pair of transects at any
given interval. Collections in each transect were conducted hourly, starting 1 h before
sunrise and ending 1 h after sunset. In addition, collections were taken 1/2 h before
sunrise and after sunset to include crepuscular periods. Sunrise occurred at about
0545 and sunset at about 1945 hours CST Each day contained 19 collection intervals
in each of the four transects.
Flies captured at each transect were recorded, identified and released. To prevent
biases in sampling previously collected flies, a small dot of brightly colored paint was
placed on the dorsum of the thorax of each fly the first time it was captured. A differ
ent color was used for each time period and day. All flies were released after marking
near their collection site. Marked flies recaptured were recorded as such and not in
cluded in final data to determine total abundance at each time interval.
Air temperature, relative humidity, wind speed and direction were recorded dur
ing each collection period. During 1994, light intensity (lux) was also recorded in each
transect using a handheld light meter (capable of recording <1 to 107,589 lux obtained
from A. W. Sperry Instruments, Inc., Hauppauge, NY,). Each light measurement was
a mean of these transect readings with the photocell pointed towards the sky, perpen
dicular to the ground. Percent cloud cover was estimated subjectively and generally

















Florida Entomologist 79(4)


did not exceed 10%. On 6 June 1994, it rained from 0400 through 1500 hours with
100% cloud cover during the majority of that day
In 1994, additional aerial net samples of C. celatus were taken at least 50 m from
the main sampling transects during the same time periods for determination of parity
and fructose-feeding. All flies collected for this purpose were placed on dry ice imme
diately after capture and kept frozen at 0C until gonotrophic dissection and fructose
assays were performed. Dissections and fructose assays were performed within one
week of collections. Thoraces were excised and assayed for presence or absence of a
fructose meal using the methods of Van Handel (1972). Results were recorded at 1 h.
Abdomens were excised during the same time fructose assays were conducted and
placed in a drop of saline solution on a slide to determine parity Parity was based on
presence or absence of tracheal dilations at the base of ovarioles (Detinova 1962). Fe
males were classified as parous (had oviposited) or nulliparous (not oviposited).
Data from collections of road and forest canopy transects were subjected to
ANOVA (PROC GLM, SAS Institute 1990). Fly collections were transformed via xx+l
prior to statistical analyses. A Student-Newman-Keuls test was used to determine
differences (P<0.05) in total fly abundance between transects (Sokal & Rohlf 1981).
Step-wise regressions were performed separately on 1994 mean light intensity
(lux) data and on pooled data means for 1993 and 1994 using relative humidity and
temperature as independent variables (Sokal & Rohlf 1981). Relative humidity and
light intensity data were log transformed prior to regression analyses.


RESULTS

A total of 521 C. celatus host-seeking females were collected during this study. The
earliest collection of C. celatus occurred during the crepuscular period one half hour
before sunrise (0530) with a primary peak at 0645 (Fig. 1). A second peak of lesser
abundance occurred at 1945 hour. In between peak periods, flies were generally
present in lower numbers. No fly activity was observed during darkness.
Chrysops celatus was found to be present and actively biting during diurnal rain
episodes on 6 June. On that day, peak activity of host-seeking flies shifted two hours
later in the morning (0845) and five hours earlier (1445) in the afternoon compared
with non-rain dates and minimal cloud cover. Relative humidity on that date ranged
from 99 to 100%, while temperature ranged from 21 to 22 C.
No significant location effects were observed for either year when total fly abun-
dance per location was compared between collections from dirt road transects and for
est canopy transects (1993-F 3.22, d.f.75, P 0.08; 1994-F 0.96, d.f. 151, P 0.33).
Of the total C. celatus marked during 1993 and 1994, 4.8% (n=25) were recaptured.
The overall majority of C. celatus (95.8%, i.e., 181 out of 189) collected near sample
transects had fed on a fructose source, while 92.1% (i.e., 174 out of 189) from these col
elections were nulliparous. Most nullipars (95.4%, i.e., 166 out of 174) were also posi
tive in the anthrone test for a fructose meal. One individual fly collected at 0545 hour
contained blood in its diverticulum.
Hourly temperature and humidity cycles appeared to coincide with peak periodic
ity of host-seeking activity of C. celatus (Fig. 1). When all three environmental param
eters: relative humidity, temperature and light intensity, were regressed against total
number of flies, the total model explained approximately 45% of the variation in diel
biting activity (Y 13.40+3.46X,-0.05X2-0.03X,, P 0.0001). Relative humidity ex
plained 93.3% of the variation in the above model (P 0.03). Light intensity (P=0.42)
was not a significant contributing factor nor was temperature (P=0.56). Similar
trends were observed with biting data from the rain date collection, however in this


December, 1996

















Cilek & Schreiber: Tabanid Host-Seeking Activity


case, relative humidity was not significant (P=0.09). Wind speed during studies from
both years did not exceed 1.6 km/h and analysis of this parameter's effect on biting ac
tivity was not conducted.

DISCUSSION

No previous reports on diel host-seeking periodicity of C. celatus exist. However,
the biphasic behavior pattern of this species was similar to that reported for C. atlan
ticus Pechuman in Connecticut (Anderson 1973) and New Jersey (Thorpe & Hansens
1978), C. flavidus Weidemann (Roberts 1974) in Mississippi, and C. dimidata Wulp
and C. silacea Austen in British Cameroons (Duke 1959). In each instance, one peak
feeding period was identified shortly after sunrise and a second peak two hours before
sunset with host-seeking activity terminating at darkness.
Temperature and humidity have been reported to influence host-seeking activity
of a variety of tabanids (Corbet 1964, Dale & Axtell 1975, Alverson & Noblet 1977,
Strickman & Hagan 1986). Chrysops celatus showed a statistically significant associ
ation with hourly humidity levels but not temperature.
We found no significant statistical association of C. celatus host-seeking behavior
with relative light intensity (P=0.78), even though light intensity has been reported
to influence the flight activity for other Chrysops spp. (Roberts 1974, Dale & Axtell
1975). However, host-seeking activity of C. celatus was prolonged the morning of 6
June 1994 (rain date) by two hours and appeared five hours earlier in the afternoon
when 100% cloud cover prevailed. These shifts are in agreement with reports by Fair


0446 0646 0746 0945 1146 1346 1546 1745 1946 2046
Time (hours)

Fig. 1. Diel host-seeking activity of Chrysops celatus and associated environmental
parameters. Total flies captured per time period (]), mean % relative humidity (-),
mean temperature C (-+-), and mean light intensity (lux -*-) from 0445 hour to 2045
hours (CST) during June 1993 and 1994, Grayton Beach, Walton Co., Florida.

















Florida Entomologist 79(4)


child & Weems (1973) and Alverson & Noblet (1977) that cloudy days often obscure ac
tivity peaks by prolonging host-seeking compared with sunny days.
On average, 4.8% (25 of 521) C celatus initially marked were recaptured. We be
lieve that the low recapture rate was not due to "panic flights" away from the sam
pling area. Rather, the majority of C celatus may have flown out of the area, after
release, to resume seeking a suitable host rather than remain in the immediate area
for another to appear. A study in Louisiana, by Foil (1983), reported that 65% of
marked Chrysops spp. (i.e., 134 out of 206) were recaptured on the same tethered
horse after being interrupted from completing a blood meal, marked in a similar fash
ion, and released 0.31 m away
It was not unusual that the majority of C. celatus collected had obtained a fructose
meal, for carbohydrates have been reported as important dietary components for ta
banids (Magnarelli et al. 1979, Magnarelli 1981) presumably to restore depleted en
ergy reserves during flight. Magnarelli et al. (1979) also reported that female C.
atlanticus and C. fuliginosus Wiedemann fed on similar reducing sugars throughout
the day. However, ground searches in our immediate area for possible fructose sources
for C. celatus revealed only sporadic blossoms of a few eastern redbud (Cercis ca
nadensis L.) and magnolia. We acknowledge that C. celatus adults may have fed on
other sources (such as cryptic extrafloral nectaries, especially in the upper canopy) at
this, and other locations, before flying into our sampling area.
The importance of identifying diel host-seeking activity is crucial if one is to nar
rowly target time intervals for control of adult C celatus. Insecticide applications ap
plied during early morning hours may partially reduce the population but because of
the apparent high mobility of these pests, new individuals probably would enter an
area soon after spraying. Although the use of traps may be considered (e.g., Snoddy
1970, Cilek 1993, French & Hagin 1995), an alternative solution, and more prudent
economical or environmentally sensitive strategy than using insecticides, would be to
avoid areas where this pestiferous tabanid is abundant during early morning and late
afternoon hours.

ACKNOWLEDGMENTS

We thank M. A. Tidwell, Department of Environmental Health, University of
South Carolina, School of Public Health, Columbia, SC for identification of Chrysops
celatus. We also acknowledge those persons that contributed critical reviews of previ
ous manuscript drafts.

REFERENCES CITED

ALVERSON, D. R., AND R. NOBLET. 1977. Activity of female Tabanidae (Diptera) in re
nation to selected meteorological factors in South Carolina. J. Med. Entomol. 14:
197-200.
ANDERSON, J. F. 1973. Biting behavior of saltmarsh deer flies (Diptera: Tabanidae).
Ann. Entomol. Soc. America. 66: 21-23.
ANDERSON, J. F. 1985. The control of horse flies and deer flies (Diptera: Tabanidae).
Myia 3: 547-598.
CILEK. 1993. The yellow-biting flies of Florida. J. A. Mulrennan, Sr. Arthropod Res.
Lab., Florida A & M Univ. Ent. Guide #1. 3 pp.
CORBET, P. S. 1964. Nocturnal flight activity of sylvan Culicidae and Tabanidae
(Diptera) as indicated by light traps: a further study. Proc. Royal Entomol. Soc.
London Ser. A 39: 53-57.
DALE, W. E., AND R. C. AXTELL. 1975. Flight of the salt marsh Tabanidae (Diptera),
Tabanus nigrovittatus, Chrysops atlanticus and C. fuliginosus: correlation with
temperature, light, moisture and velocity. J. Med. Entomol. 12: 551-557.


December, 1996

















Cilek & Schreiber: Tabanid Host-Seeking Activity


DETINOVA, T. S. 1962. Age-grouping in Diptera of medical importance. World Health
Org. Monog. Ser. 47.
DUKE, B. O. L. 1959. Studies on the biting habits of Chrysops. VI. A comparison of the
biting habits, monthly biting densities and infection rates of C silacea and C.
dimidata (Bombe form) in the rain forest of Kumba, Southern Cameroons, U. U.
K. A. Ann. Trop. Med. Parasitol. 53: 203-214.
FAIRCHILD, G. B., AND H. V. WEEMS. 1973. Diachlorus ferrugatus (Fabricius), a fierce
biting fly (Diptera: Tabanidae). Florida Dept. Agric. Consum. Serv., Div. Plant
Industry, Entomol. Circ. 139.
FOIL, L. 1983. A mark-recapture method for measuring effects of spatial separation of
horses on tabanid (Diptera) movement between hosts. J. Med. Entomol. 20:
301-305.
FRENCH, F. E., AND D. V. HAGAN. 1995. Two-tier box trap catches Chrysops atlanticus
and C fuliginosus (Diptera: Tabanidae) near a Georgia salt marsh. J. Med. En
tomol. 32: 197-200.
HARWOOD, R. F., AND M. T. JAMES. 1979. Entomology in human and animal health.
Macmillan Publishing Company, New York.
JONES, C. M., AND D. W. ANTHONY. 1964. The Tabanidae (Diptera) of Florida. USDA,
Agric. Res. Serv. Tech. Bull. 1295.
MAGNARELLI, L. A. 1981. Sugar feeding by female tabanids (Diptera: Tabanidae) and
its relation to gonotrophic activity. J. Med. Entomol. 18: 429-433.
MAGNARELLI, L. A., J. F. ANDERSON, AND J. H. THORNE. 1979. Diurnal nectar-feeding
of salt marsh Tabanidae. Environ. Entomol. 8: 544-548.
MEASE, J. A. 1943. Deer fly desensitization. J. American Med. Assoc. 122: 227.
ROBERTS, R. H. 1974. Diurnal activity of Tabanidae based on collections in Malaise
traps. Mosq. News 34: 220-223.
SAS INSTITUTE. 1990. SAS user's guide: statistics, version 6 ed. SAS Institute, Cary,
NC.
SNODDY, E. L. 1970. Trapping deer flies with colored weather balloons (Diptera: Ta
banidae). J. Georgia Entomol. Soc. 5: 207-209.
SOKAL, R. R., AND F. J. ROHLF. 1981. Biometry (2 ed.), W H. Freeman and Co., San
Francisco.
STRICKMAN, D., AND D. V. HAGAN. 1986. Seasonal and meteorological effects on activ
ity of Chrysops variegatus (Diptera: Tabanidae) in Paraguay. J. American Mosq.
Control Assoc. 2: 212-216.
THORPE, K. W., AND E. J. HANSENS. 1978. Diurnal activity of Chrysops atlanticus:
some questions concerning sampling techniques. Environ. Entomol. 7: 871-873.
VAN HANDEL, E. 1972. The detection of nectar in mosquitoes. Mosq. News 32: 458.

















Florida Entomologist 79(4)


SPINOSAD BAIT FOR THE CARIBBEAN FRUIT FLY
(DIPTERA: TEPHRITIDAE)

JIMMIE R. KING AND MICHAEL K. HENNESSEY
USDA-ARS, Subtropical Horticulture Research Station, Miami, FL

ABSTRACT

The establishment of the Caribbean fruit fly, Anastrepha suspense (Loew), in Flor
ida resulted in the need for quarantine treatments of citrus for shipment to certain
states and countries. The state of Florida has established a fly-free protocol that per
mits shipment from areas in compliance without further treatment. One option of the
protocol calls for the use of a toxic bait cover spray; however, sprays containing
malathion are required to contain 190,000 ppm active ingredient. Thus, alternative
pesticides are needed because of environmental, human health, and property damage
concerns with malathion. Spinosad, an extract of a bacterial broth, is a contact and
stomach poison for target pests. It was combined with a sugar-yeast hydrolysate mix
ture and tested as a bait spray on colony-reared adult flies in a no-choice test. The EC,9
values were estimated to be 9.4 and 5.8 ppm for sexually mature females and males,
respectively. These relatively low values indicate that spinosad is an excellent candi
date for field testing.

Key Words: Pesticide, Anastrepha suspense, citrus, quarantine

RESUME

El establecimiento en la Florida de la mosca de la fruta del Caribe., Anastrepha
suspense (Loew), ha hecho que las frutas citricas enviadas a ciertos estados y paises
reciban tratamientos cuarentenarios. El estado de la Florida ha establecido un proto
colo para areas libres de moscas que permit el envio de frutas de las areas que cum
plan con el mismo, sin requerir tratamiento. Una opci6n del protocolo es la de cubrir
las frutas con un cebo t6xico. Sin embargo, es requerido que la cubierta contenga
190,000 ppm de malathion como ingredient active. Por lo tanto, se necesitan otras al
ternativas en cuanto a insecticides porque el uso del malathion es danino al ambiente
y la salud humana. Spinosad, un extract de caldo de bacteria, es un veneno de con
tacto y estomacal para esta plaga. El Spinosad fue combinado con una mezcla de azu-
car y levadura hidrolizada y probado como cebo de aspersion en moscas adults de
una colonia de laboratorio, en una prueba sin opcidn. Los valores de EC,, fueron esti
mados en 9.4 y 5.8 ppm respectivamente para hembras y machos maduros sexual
mente. Estos valores relativamente bajos indican que el Spinosad es un excelente
candidate para pruebas de campo.





Florida citrus exported to foreign countries and domestic citrus producing areas
must meet certain quarantine requirements to prevent the spread of the Caribbean
fruit fly, Anastrepha suspense (Loew)(Diptera:Tephritidae). The Florida caribbean
fruit fly protocol is a body of regulations that allows fresh citrus fruit to be certified
free of the Caribbean fruit fly and shipped to Japan, California, Texas, Bermuda, and
Hawaii. One option of the certification procedure requires that a bait spray, composed
of 20% technical grade malathion (typically 95% purity) and 80% Nulure" by volume
(190,000 ppm malathion), be aerially applied to groves every 7-10 days during harvest


December, 1996

















King & Hennessey: Spinosad-Caribbean Fruit Fly Bait 527

to eradicate adults (Riherd et al. 1994). The use of malathion bait in Mediterranean
fruit fly, Ceratitis capitata (Wiedemann), eradication programs has met with much
criticism by the public because of concerns about damage to automobile finishes in
Florida (Anonymous 1992) and human health risks in California (Kahn et al. 1992,
Russell et al. 1994). These problems with the usage of malathion indicate that an al
ternative bait is needed.
Spinosad is the common name of a mixture of Spinosyn A and Spinosyn D with
CAS Registry numbers of 131929-60-7 and 131929-63-0, respectively The spinosyns
are a naturally-derived group of molecules from a bacteria, Actinomycetes: Saccha
ropolyspora spinosa (Mertz & Yao 1990).


MATERIALS AND METHODS

The methodology generally followed is that previously reported for Caribbean fruit
fly bioassays of abamectin in bait (Hennessey & King 1996). The flies were from a col
ony which has been maintained since 1971 at the Miami ARS laboratory (24-27 C, 70
85% RH) and protected from exposure to insecticides. The flies used in this study were
reared as larvae on agar-based diet (Hennessey 1994) and fed as adults on a mixture
consisting of 25% yeast hydrolysate enzymatic powder (ICN Biochemicals, Inc., Cleve
land, OH) and 75% sugar. Two-week-old males and females were removed from a
stock cage with a vacuum hose and placed in a test cage (0.16 m3, 9 12 flies per cage).
Female flies at two weeks of age were considered to be fertilized and ready to oviposit.
Tests were carried out over 48 h in an environmental chamber (28-30 C, 85-95% RH,
photoperiod 14:10 (L:D), fluorescent light). Flies were deprived of food, but not water
(agar-water gel), 1 2 h before testing. During testing, flies had access to agar-water gel
and spinosad bait in no-choice tests.
A sample (55 ml, Lot #B721-24, formulation NAF-85, DowElanco, Indianapolis,
IN) of spinosad, which was supplied by the manufacturer and specified to contain
45.9% active ingredient, was used in all tests. A stock solution (2.50 mg/ml) was pre
pared for each test by dilution of 544.7 mg of the above sample with 95% ethanol to
100 ml in a volumetric flask. Appropriate dilutions were prepared using 95% ethanol
such that 0.1 ml added to 5 g bait would give the desired test dose levels of 50, 25, 10,
7, 4, 2, 1, 0.5 and 0.1 ppm. The bait was essentially the same as the food used for feed
ing adult flies in the colony except for water content. Stock bait was prepared by com
bining 25 ml distilled water and 40 g sucrose in a 250 ml beaker and heating with
stirring until the sucrose dissolved. After cooling the solution to ambient tempera
ture, 10 g yeast hydrolysate was added to the solution and manually mixed with a
stirring rod until a homogeneous mixture was formed. For each dose level to be tested,
5 g of the stock bait was weighed into a 16 ml vial and 0.1 ml of test solution was added
using a dispensing pipette. The vial was sealed with a Teflon-lined cap and the con
tents of the vial were mixed by manual shaking and also by stirring just prior to spot
ting.
Bait was manually applied to the bottom of 15 cm glass petri dishes using dispos
able dropping pipets (20-30 droplets, 2-3 mm diam, 0.15 to 0.16 g total per dish). Two
dishes were prepared for each dose level (0, 0.1,0.5, 1,2, 4, 7, 10, 25, and 50 ppm). The
bait was allowed to dry at ambient temperature for 24 h before testing. At the begin
ning of each test, a petri dish was placed in each cage (droplet side down) and sup
ported by three small clothespins 2 cm above the floor of the cage. The top side of the
dish was covered with translucent brown masking tape to inhibit flies walking under
the dish from flying upward and getting stuck in the bait. Cages were randomly dis
tribute within the incubator with respect to dose.

















Florida Entomologist 79(4)


Irreversible knockdown followed by death (assessed visually) of the flies after 24
and 48 h exposure was the criterion used to determine the effective concentration
(EC). Five replications of the experiment, each conducted on a different date, with two
replicates of each spinosad concentration per date, were done for each sex. Sexes were
tested separately. Each test utilized a different generation (batch) of flies from colony
production. All test apparatus was thoroughly washed between tests. Values of EC,0s,
EC,,s, and 95% fiducial limits (FL) were calculated using probit analysis (SAS Insti
tute 1992). The LOG 10 option was used because it gave the best fit of the data.


RESULTS AND DISCUSSION

Adults were observed to feed on the bait droplets at all concentrations of spinosad
with no apparent repellency even at the maximum dose tested. It has been previously
documented that two-week-old Caribbean fruit flies consume sugar and protein at a
high rate and that protein feeding was higher at that age for females than for males
(Landolt & Davis-Hernandez 1993).
Mean percentages of female flies knocked down ranged from 2 to 99% at 24 h and
5 to 100% at 48 h for bait containing 0 to 50 ppm spinosad, respectively (Table 1). For
male flies knockdown ranges were 1 to 100% and 3 to 100% for exposures of 24 and 48
h, respectively (Table 1).
The EC,0 and EC,, predicted from probit analysis for females at 24 h were 4.6 and
23.8 ppm, respectively (Table 2). At 48 h the EC,, and EC,, were reduced to 2.6 and 9.4
ppm, respectively The fiducial limits were also reduced from 3.3-5.9 ppm and 14.3
81.5 ppm at 24 h to 1.7-3.4 ppm and 5.9-43.5 ppm at 48 h for the EC,0 and EC,,, re
spectively (Table 2). At 24 h the EC,0 (3.4 ppm) for males was slightly lower than for
females and the EC,, (27.1 ppm) was slightly higher but the fiducial limits overlapped
in both cases (Table 2). Previous results obtained using a similar bait with abamectin
showed that a lower dosage was required for an ECQ0 and EC,, for females than males
at 24 and 48 h (Hennessey & King 1996). At 48 h the values of both the EC,0 (1.2 ppm)
and EC,, (5.8 ppm) for males were slightly lower than the corresponding values for fe

TABLE 1. MEAN PERCENTAGES (+SEM) OF CARIBBEAN FRUIT FLIES IRREVERSIBLY
KNOCKED DOWN IN CAGE TESTS WITH SPINOSAD IN BAIT AT 10 CONCENTRA
TIONS.

Females Males
Concentration,
ppm 24 h 48 h 24 h 48 h

0 2.0+1.3 5.0+2.1 3.0+1.4 4.0+1.5
0.1 4.9+2.9 6.8+3.1 1.0+0.9 3.1+1.5
0.5 2.9+2.7 7.0+2.7 1.0+0.9 6.0+3.8
1 3.8+1.5 11.0+1.7 7.0+3.5 41.8+7.3
2 7.0+2.8 30.0+5.3 21.2+5.3 78.5+4.6
4 50.9+5.6 88.8+2.7 70.4+4.8 98.0+1.3
7 75.7+6.2 95.9+1.6 77.7+3.7 99.0+0.9
10 94.1+1.5 100+0 96.3+2.7 100+0
25 97.0+1.4 99.0+0.9 95.5+2.7 100+0
50 99.0+0.9 100+0 100+0 100+0


December, 1996

















King & Hennessey: Spinosad-Caribbean Fruit Fly Bait 529

TABLE 2. EC',, AND EC,, OF SPINOSAD IN BAIT AT 24 H AND 48 H TO FEMALE AND MALE
CARIBBEAN FRUIT FLIES IN CAGE TESTS.

Females

24 h 48 h

ECo, 4.6 2.6
95% FL 3.3-5.9 1.7-3.4
EC9, 23.8 9.4
95% FL 14.3-81.5 5.9-43.5

Males

24 h 48 h

ECo, 3.4 1.2
95% FL 2.5-4.3 1.1-1.4
EC9, 27.1 5.8
95% FL 15.9-75.3 4.6-8.1

1Effective concentration, ppm.


males (Table 2). The probit curves of predicted knockdown versus the logarithm (base
10) of concentration exhibits an unusually high slope and indicates that spinosad con
centrations in the low ppm range will be suitable at 24 or 48 h for >99% mortality (Fig.
1).
Compared to the present protocol which requires 190,000 ppm of malathion in bait
in the Caribbean fruit fly-free spray program, spinosad offers a very promising alter
native since a dose of only 100 ppm is an order of magnitude greater than that re
quired for an EC of 99% for females or males. Spinosad (NAF-85) has been shown to
have LC,0 levels of >200 ppm when tested as a contact and stomach poison against se
elected hemipteran, coleopteran, neuropteran, and acarine beneficial species
(Schoonover & Larson, 1995). Additional data, provided by DowElanco (Spinosad
Technical Guide), indicates that the effects of spinosad, relative to the environment,
mammals, birds, fish, various aquatic organisms, and beneficial insects, are favorable.
The acute oral toxicity for mice, rats, bobwhite quail, and mallard ducks, based on
LD0o values, were all >2000 mg/kg. The acute dermal toxicity for rabbits was also
>2000 mg/kg. Spinosad is highly toxic to honey bees when administered as a topical
application, but when toxicity was evaluated in field-sprayed apple blossoms no sta
tistical difference in mortality was observed between the treated and control groups.
Assessments of potential exposures and risks to workers using spinosad to spray cot
ton at a level of 202.3 g active ingredient per acre indicated a margin of exposure of
1,800 for the worst case, i.e. the mixer and loader for aerial spraying. The application
of 12 ounces of spray bait with 100 ppm active ingredient, which is 10 times the max
imum required to achieve an LD,, mortality observed in this study, requires only 0.034
g spinosad per acre and the safety factor is even greater. These considerations, plus
the low dosage requirements,justify field tests to determine more precisely those con
centrations of spinosad that will be effective for fruit fly control under grove condi
tions.














Florida Entomologist 79(4)


100-

90-

80-

70-

60-

50-

40-

30-

20-

10-

0-


/








Ii


7


i.ii 141 IlilIj III '11111111 II II I I I


0 10


Concentration, ppm
Fig. 1. Probit curve of predicted percentage knockdown and death of Caribbean
fruit flies at various concentrations of spinosad after exposure times of 24 and 48 h.

ACKNOWLEDGMENTS
We thank Pauline Mendez, Gordon Millard, Elena Schnell, and Wilhelmina Wasik
for assistance with experiments. Mention of a proprietary product does not constitute
its endorsement by the USDA.

REFERENCES CITED
ANONYMOUS. 1992. Questions and answers on malathion. Florida Dept. Agric. and
Consumer Services, leaflet. 3 pp.
HENNESSEY, M. K. 1994. Depth of pupation of Caribbean fruit fly (Diptera: Tephriti
dae) in soils in the laboratory. Environ. Entomol. 23: 1119-1123.
HENNESSEY, M. K., AND J. R. KING. 1996. Abamectin bait for Caribbean fruit fly
(Diptera: Tephritidae). J. Econ. Entomol. 88: 000-000.
KAHN, E., M. BERLIN, R. J. JACKSON, AND J. W. STRATTEN. 1992. Assessment of acute
health effects from the medfly eradication project in Santa Clara County, Cali
fornia. Arch. Environ. Health 47: 279-284.
LANDOLT, P. J., AND K. M. DAVIS-HERNANDEZ. 1993. Temporal patterns of feeding by
Caribbean fruit flies (Diptera: Tephritidae) on sucrose and hydrolyzed yeast.
Ann. Entomol. Soc. America 86: 749-755.


Female 48 h
........ Male 48 h

SFemale 24 h
---- Male 24 h


___


December, 1996


"1 . . I ........." ""11 T I I.. I

















King & Hennessey: Spinosad-Caribbean Fruit Fly Bait 531

MERTZ, F. P., AND R. C. YAO. 1990. Saccharopolyspora spinosa sp. nov. isolated from
soil collected in a sugar mill rum still. Int. J. Syst. Bacteriol. 40: 34-39.
RIHERD, C., R. NGUYEN, AND J. R. BRAZZEL. 1994. Pest free areas, pp. 213-223 in J. L.
Sharp and G. J. Hallman [eds.], Quarantine treatments for pests of food plants.
Westview, Boulder, CO.
RUSSELL, H., A. M. FAN, M. DIBARTOLOMEIS, C. ARNESEN, J. STRATTON, AND R. J.
JACKSON. 1994. Integrating risk in management and risk communication into
a risk assessment of a medfly eradication project in California. J. Hazard. Ma
trials 39: 267-278.
SAS INSTITUTE. 1992. SAS user's manual version 6.04. SAS Institute, Cary NC.
SCHOONOVER, J. R., AND L. L. LARSON. 1994. Laboratory activity of spinosad on non
target beneficial arthropods. Arthropod Management Tests 20: 357.
SPINOSAD TECHNICAL GUIDE. DowElanco, Indianapolis, IN.


++++++++++++++++++++++++++++++++++++++++++++++++++++
















Lobinske et al.: Chironomidae in Wekiva Tributaries


QUALITATIVE AND QUANTITATIVE STUDIES ON
CHIRONOMIDAE (DIPTERA) AND SELECTED
PHYSICO-CHEMICAL PARAMETERS IN TWO TRIBUTARIES
OF THE WEKIVA RIVER, CENTRAL FLORIDA

RICHARD J. LOBINSKE'.2, ARSHAD ALI' AND I. JACK STOUT2
'University of Florida, Institute of Food and Agricultural Sciences
Central Florida Research and Education Center, 2700 East Celery Ave.
Sanford, FL 32771

2University of Central Florida, Department of Biology, 4000 Central Florida Blvd.
Orlando, FL 32816.

ABSTRACT

Aquatic midge (Chironomidae: Diptera) larval densities, 24-h adult emergence,
and larval and adult dry biomass were estimated monthly for two years in two tribu
taries of the Wekiva River, central Florida, along with selected physico-chemical wa
ter parameters. Twenty-four genera of midges were identified in Blackwater Creek
and 26 in Rock Springs Run, with subfamily Chironominae dominating the midge
fauna. Larval densities in the former stream ranged from 56 to 757 per m2, with 24-h
periods adult emergence ranging from 0 to 95 per m2. The latter stream supported 138
to 1277 larvae per m2 with 0 to 68 emergent adults per m2 taken during 24-h periods.
Mean larval biomass in Rock Springs Run (42 mg per m2) was significantly (P<0.05)
higher than in Blackwater Creek (27 mg per m2), while mean adult biomass in both
habitats was essentially identical (1.1 mg per m2). Annual midge productivity esti
mates (1.12 g dry wt per m2) in each stream indicated that both were oligotrophic. Wa
ter volume was the overriding abiotic factor noted in both habitats, influencing many
of the observed water parameters and altering the midge generic composition, espe
cially in Blackwater Creek.

Key Words: Chironomidae, midges, populations, productivity, seasonal changes,
streams, physico-chemical parameters

















Florida Entomologist 79(4)


RESUME

Las densidades larvales de moscas de agua (Chironomidae: Diptera), la emergen
cia de adults en 24 horas, y la biomasa larval y de adults, asi como parametros fi
sico-quimicos de agua seleccionados, fueron determinados mensualmente durante dos
anos en dos tributaries del rio Wekiva, en Florida Central. Fueron identificados 24 g6-
neros de moscas de agua en el arroyo Blackwater y 26 en Rock Springs Run, con la
subfamilia Chironominae dominando la fauna de moscas de agua. Las densidades lar
vales en la primera corriente estuvieron en el rango de 56-757 por m2, con adults
emergidos en 24 h en el rango de 0-65 por m2. La ultima corriente tuvo 138-1277 lar
vas por m2 con 0-68 adults emergentes por m2 tomados durante periods de 24 h. La
biomasa media larval en Rock Springs Run (42 mg por m2) fue significativamente
(P<0.05) mas alta que en el arroyo Blackwater (27 mg por m2), mientras que la bio
masa de adults en ambos habitats fue esencialmente id6ntica (1.1 mg por m2). Los es
timados de producci6n annual (1.12 g de peso seco por m2) en cada corriente indicaron
que ambas fueron oligotr6ficas. El volume de agua fue el factor abi6tico mas impor
tante encontrado en ambos habitats, inluenciando muchos de los parametros de agua
observados y alterando la composici6n generica de las moscas de agua, especialmente
en el arroyo Blackwater.





In inland aquatic ecosystems, Chironomidae (Diptera) often are among the domi
nant macroinvertebrates and one of the most important components of aquatic food
chains (Tokeshi 1995a). This is particularly true for Florida, where almost 25% of the
state's land is covered with swamps (Ewel 1990), marshes (Kushlan 1990), lakes
(Brenner et al. 1990) or streams (Nordlie 1990). Although chironomid midges are re
garded as important organisms in all of these ecosystems, very little information on
their quantitative or qualitative composition is presently available, and this is specif
ically true for lotic systems.
The present investigation was undertaken in two tributaries of the Wekiva River,
central Florida. Qualitative and quantitative samples of midge larvae and emergent
adults were collected monthly from each stream for two years to assess the midge lar
val and adult densities and productivity. Selected physico-chemical parameters in
both habitats were also measured to elucidate their influence on the midge popular
tions.


METHODS AND MATERIALS

The study streams were in the Wekiva River basin (a part of the St. Johns River
basin) in central Florida (Fig. 1). Blackwater Creek is about 40 km long second order
sand bottom stream with both calcareous and swamp-bog stream aspects (Beck 1965).
Rock Springs Run is a first order calcareous stream (Beck 1965) about 14.5 km long.
Water current in both streams varied from 2-50 cm per sec; local variation in current
velocity resulted in substrates which varied from exposed sand to thick deposits of de
tritus and silt.
For sampling chironomid larvae and adults and for measuring selected physico
chemical parameters, 10 sampling stations were selected in each stream. The exact loca
tions of the sampling stations were determined by coordinates using a Panasonic model
LX-G5500 Global Positioning System receiver (Panasonic Company, Secaucus, NJ).
Each stream was sampled (for 2 days) monthly from February 1993 to January
1995. Each sample series was collected between 0830 and 1230 local time. On day 1,


December, 1996















Lobinske et al.: Chironomidae in Wekiva Tributaries


0 1 23 45
Kilometers

St. Johns River



Sulfur Run f


Rock


Little Wekiva River


Wekiwa Springs


Fig. 1. Map of the Wekiva River Basin, central Florida, with Blackwater Creek and
Rock Springs Run study areas marked by boxes. Relative location of area map is
shown on outline map of Florida.


a 0.25 m2 emergence cone trap (Ali 1996) was randomly placed on the stream bottom
at each location. Also, selected physical and chemical parameters were measured in
situ close to the sediment/water interface at or very near each sampling station with
portable meters or appropriate field kits. The parameters included: current velocity

















Florida Entomologist 79(4)


(Model 2030R mechanical flowmeter, General Oceanics Company, Miami, FL), pH
(Model 107 pH meter, Corning Glass Works, Corning, NY), dissolved oxygen (Model
54A dissolved oxygen meter, Yellow Springs Instrument Company Inc., Yellow
Springs, OH), turbidity (Model DRT 1000 nephelometer, HF Instruments, Bolton, On
tario or a Mini 20 portable spectrophotometer fitted with a nephelometer module, Mil
ton Roy Company, Rochester, NY), nitrate-N (Model NCR kit, LaMotte Company,
Chestertown, MD), conductivity and water temperature (Model 140 conductivity-tem
perature-salinity meter, Orion Research Inc., Boston, MA). Secchi disk transparency
was measured with a 20 cm Secchi disk connected to a vertical steel rod. For statisti
cal analysis, pH was converted to H' concentration.
On day 2 of monthly samplings, chironomid larval and adult samples were col
elected. One benthic sample was collected from each station at about 1 m or less up
stream of the cone sample area with a 15 x 15 x 15 cm Ekman dredge mounted on a
1.5 m steel pole (APHA 1992). Benthic samples were immediately washed through a
350 pm pore screen and stored on ice until returned to the laboratory. Adult samples
were collected from the cone traps using the procedure of Mulla et al. (1974).
All benthic and adult samples were examined for Chironomidae and analyzed
within 48 h using standard methods, (APHA 1992, Ali et al. 1977). Midge larvae were
identified (under 40-400x magnification) to genus using the keys of Epler (1992),
while the adults were examined under 40x magnification to determine their subfam
ily or tribe using the keys provided by Weiderholm (1989). Time constraints and dam
age to specimens during drying for biomass determination purposes prevented
further identification of adults. Larval as well as adult dry biomasses were deter
mined using the method of Dermott & Paterson (1974).
Rainfall data (30-day cumulative) provided by the Florida Department of Environ
mental Protection, Division of Recreation and Parks for Wekiwa Springs State Park
(1800 Wekiwa Circle, Apopka, FL) were used to estimate water inputs to Rock Springs
Run. Water volume for Blackwater Creek was estimated from 30-day mean water el
evation data provided by the United States Geologic Survey, Water Resources Divi
sion (224 W Central Parkway, Altamonte Springs, FL) from gauging station
02235200.
Productivity of midges was estimated using the formula of Iwakuma (1986).
Statistical analysis of collected data and their graphical presentation was made by
utilizing Instat V. 2.04 (Graphpad Software, Inc., San Diego, CA) and SlideWrite Plus
V. 6.0 (Advanced Graphics Software, Inc., Carlsbad, CA).


RESULTS

Larvae of 24 chironomid genera belonging to subfamilies Chironominae (tribes
Chironomini and Tanytarsini), Tanypodinae and Orthocladiinae were identified in
Blackwater Creek whereas 26 genera occurred in Rock Springs Run (Table 1). Trends
of monthly mean midge larval densities, emergent adults and dry biomass for both
streams are shown in Fig. 2. Midge larval density in Blackwater Creek ranged from
56 to 757 per m2 and emergent adults from 0 to 95 per m2: Rock Springs Run from 138
to 1277 per m2 (larvae) and from 0 to 68 per m2 (adults). Midge dry biomass in Black
water Creek varied from 0.9 to 88.8 mg per m2 (larvae) and 0.0 to 2.5 mg per m2
(adults) and in Rock Springs Run from 13.3 to 114.4 mg per m2 (larvae) and 0.0 to 2.6
mg per m2 (adults).
Members of the tribe Chironomini were the most abundant midges, comprising
47.0% of total midge larvae (n=1926) during the study period in Blackwater Creek
(BC) and 55.8% of the total (n=2473) in Rock Springs Run (RSR). This was followed


December, 1996

















Lobinske et al.: Chironomidae in Wekiva Tributaries


TABLE 1. LIST OF CHIRONOMID LARVAL GENERA AND PERCENT COMPOSITION OCCUR
RING IN BLACKWATER CREEK AND ROCK SPRINGS RUN, CENTRAL FLORIDA
(FEBRUARY 1993 TO JANUARY 1995).

Blackwater Creek Taxon Percent Rock Springs Run Taxon Percent


Chironomini
Chironomus
Cryptochironomus
Cryptotendipes
Demicryptochironomus
Dicrotendipes
Fissimentum
Paracladopelma
Paralauterborniella
Phaenopsectra
Polypedilum
Pseudochironomus
Stenochironomus
Stictochironomus
Tanytarsini
Cladotanytarsus
Paratanytarsus
Tanytarsus
Tanypodinae
Ablabesmyia
Clinotanypus
Paramerina
Procladius
Tanypus
Orthocladiinae
Cricotopus-Orthocladius
Epoicacladius
Thienemanniella


Chironomini
Apedilum
Chironomus
Cryptochironomus
Cryptotendipes
Demicryptochironomus
Dicrotendipes
Fissimentum
Microtendipes
Paracladopelma
Paralauterborniella
Phaenopsectra
Polypedilum
Pseudochironomus
Stelechomyia
Stenochironomus
Tanytarsini
Cladotanytarsus
Paratanytarsus
Tanytarsus
Tanypodinae
Ablabesmyia
Clinotanypus
Paramerina
Procladius
Tanypus
Orthocladiinae
Cricotopus-Orthocladius
Epoicacladius
Thienemanniella


by Tanytarsini (33.6% BC and 31.6% RSR), Tanypodinae (15.4% BC and 8.1% RSR)
and Orthocladiinae (4.0% BC and 4.5% RSR). Tanytarsus van der Wulp was the most
common genus (29.7% of total larvae) in Blackwater Creek, followed by Fissimentum
Cranston & Nolte (15%) and Polypedilum Kieffer (11.9%). Fissimentum was recently
described by Cranston & Nolte (1996) from the previously described larval taxon, Chi
ronomini Genus A Roback. In Rock Springs Run, Polypedilum was the most common
midge (21.4% of total midges), followed by Cladotanytarsus Kieffer (16.4%), Tanytar
sus (13.7%), and Pseudochironomus Malloch (13.4%).
























Florida Entomologist 79(4)


December, 1996


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ANOVA of chironomid subfamily or tribe abundance with the Friedman nonpara
metric repeated measures test found significant (P<0.0001) differences in Blackwater
Creek (Fr 49.19) and Rock Springs Run (Fr 57.96). Based on Dunn's Multiple Com-
parison as the post test, Chironomini were significantly (P<0.001) more numerous
than all other higher taxa and Tanytarsini were significantly (P<0.001) more number
ous than Orthocladiinae in both streams. Rock Springs Run supported a significantly
(P<0.05) greater mean larval dry biomass (Student's test, t=2.13, n=21).
Among emergent adults, Chironomini were the most common, comprising 56.3%
and 61.3% of total for Blackwater Creek (n 1866) and Rock Springs Run (n 1812), re
spectively This was followed by Tanytarsini (32.8% BC and 24.2% RSR), Tanypodinae
(7.7% BC and 10.3% RSR), and Orthocladiinae (3.2% BC and 4.3% RSR). Significant
(P<0.001) differences were found in abundance among higher taxa in Blackwater
Creek (Fr=56.57) and Rock Springs Run (Fr=53.15) using the Friedman repeated
measures test. Post tests revealed densities of Chironomini and Tanytarsini signifi
cantly (P<0.001) higher than Orthocladiinae in both streams, Tanytarsini higher
(P<0.05) than Tanypodinae in Rock Springs Run and Tanypodinae higher (P<0.05)
than Orthocladiinae in Blackwater Creek.
Trends of selected physico-chemical water parameters in both habitats are shown
in Fig. 3. Water volume in both streams significantly influenced some parameters, as
indicated by inverse correlations (Pearson r) with dissolved oxygen, nitrate-N, and pH
in both streams. Water elevation was inversely correlated with conductivity and Sec
chi disk transparency in Blackwater Creek, and rainfall was correlated with turbidity
in Rock Springs Run (Table 2).
Mean midge larval density and dry biomass were analyzed by linear correlation
(Pearson r) against monthly mean physico-chemical parameters. Chironomini in both
streams were significantly (P<0.05) correlated with current, with pH in Rock Springs
Run and inversely correlated with temperature in Blackwater Creek (Table 3). Tany
tarsini were inversely correlated with temperature in Blackwater Creek. Tanypodi
nae were inversely correlated with current in both streams, as well as conductivity
and nitrate-N in Blackwater Creek and correlated with water elevation in Blackwater
Creek. Orthocladiinae were correlated with pH in both streams and inversely corre
lated with water elevation in Blackwater Creek. Mean total larval density and larval
biomass were inversely correlated with temperature in Blackwater Creek.
For both streams the Iwakuma (1986) formula gave an overall mean chironomid
productivity value of 1.1+0.8 g dry wt per m2 per year. The P/B ratios of midges in
Blackwater Creek and Rock Springs Run were 40.7 and 26.2, respectively.

DISCUSSION

Based on the criteria of Tokeshi (1995b), the study streams were considered olig
otrophic because of their low (1.1 g per m2) annual chironomid productivity. The re
corded water nitrate-N levels, generally in the oligotrophic-mesotrophic range
(Wetzel 1983), and low recorded conductivity values further support this classifica
tion. This is in agreement with the findings of Duarte & Canfield (1990) for Rock
Springs Run. The high seasonal and geographic variability found in the midge larval
and adult data can be attributed to a number of sources. Microhabitat differences,
random disturbances, seasonal changes and resource partitioning all contribute to
very heterogenous distributions of midge populations (Rae 1985, Schmid 1993, Ruse
1994). Sampling deficiencies, such as possible larval loss due to washing, as well as
the limited sample size and number may have contributed to the variability. To date,
no definite means are available to accurately estimate benthic chironomid larval den
sity (Tokeshi 1995c).





















Florida Entomologist 79(4)


December, 1996


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Lobinske et al.: Chironomidae in Wekiva Tributaries


TABLE 2. MATRIX OF SIGNIFICANT (P<0.05) PEARSON CORRELATION COEFFICIENTS OF
30-DAY MEAN WATER ELEVATION (FOR BLACKWATER CREEK) AND 30-DAY CU
MULATIVE RAINFALL (FOR ROCK SPRINGS RUN) WITH SELECTED PHYSICO
CHEMICAL WATER PARAMETERS FOR BLACKWATER CREEK AND ROCK SPRINGS
RUN, CENTRAL FLORIDA (FEBRUARY 1993 TO JANUARY 1995).

Water Elevation Cumulative Rainfall
Parameter Blackwater Creek Rock Springs Run

Dissolved Oxygen 0.609 0.723
Specific Conductivity 0.706 ns
Nitrate-N 0.789 0.559
pH 0.794 0.721
Secchi Disk Transparency 0.773 ns
Turbidity ns 0.407

ns Not significant (P>0.05)


Soponis (1980) reported 42 chironomid genera identified from pupal exuviae in
Turkey Creek, a first order spring run in north Florida (Gadsden County) and Matt
son et al. (1995) reported 68 from the Suwannee River basin in north central Florida.
The 24-26 midge genera found in the present study are considerably less than the
number reported for parts of north Florida, but greater than the 10 genera reported
by Cowell & Carew (1976) in a tributary of the Hillsborough River south of the study
area in west central Florida. While smaller numbers of genera may be expected in a
smaller sample area, the peninsula effect may also influence the faunal diversity of
these study streams (Webb 1990). Nevertheless, the generic paucity in the study
streams is compatible with the 26 chironomid genera found by Ferrington etal. (1993)
in a second-order rainforest stream in El Verde, Puerto Rico.
Chironomid populations at middle latitudes show a direct correlation with water
temperature (Pinder 1995) as also noted in Rock Springs Run. The inverse relation
ship of chironomids with water temperature in Blackwater Creek is unusual but not
unprecedented. Ferrington et al. (1993) reported a similar response with chironomid
emergence in Puerto Rico. Beck (1977) reported that species of several chironomid
genera (also found in the present study) have winter emergence in the southeastern
United States.
Water volume appeared to be the dominant abiotic factor influencing midge popu
nations during the study period, especially in Blackwater Creek. Changes in water vol
ume significantly altered the physico-chemical conditions of the streams (probably by
dilution), consequently influencing midge populations.
The abundance of Chironomini in faster currents in both streams was anticipated.
Many Chironomini use spun nets to capture food. Faster currents increase the effi
ciency of the nets, thus allowing better feeding and survival (Walshe 1951). Tanypod
inae larvae tend to be free-living, thus more susceptible to drift in faster currents
(Pinder 1995), as depicted by inverse correlations of these larvae with current velocity
in both habitats.
Many chironomids are sensitive to acidification (Beck 1977). Evidence of this reac
tion was found for Orthocladiinae in both streams, and Chironomini in Rock Springs
Run. Beck (1977) reported many species of genera found in these systems to be alka
liphilous.




















Florida Entomologist 79(4)


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Lobinske et al.: Chironomidae in Wekiva Tributaries


Chironomids are a critical component of the benthos of these streams. Even at an
oligotrophic level, midge productivity for an entire stream becomes very important.
Using a hypothetical 5 m width, Rock Springs Run would have an annual midge pro
ductivity of 81 kg dry wt and Blackwater Creek 226 kg dry wt. The high P/B ratios
noted indicate a rapid overturn of biomass by these organisms. This secondary pro
ductivity represents a tremendous potential for nutrient cycling and energy flow. No
published data on productivity of chironomids in other streams in Florida are avail
able at present for comparison.
This study provides an initial database on lotic chironomid production in two Flor
ida streams. These streams were relatively unpolluted and of oligotrophic nature,
with year-round chironomid activity. This investigation warrants further laboratory
and/or field studies to discern the influences of environmental and chemical parame
ters in regulating spatial and seasonal changes of chironomid populations in the two
habitats.

ACKNOWLEDGMENTS

Gratitude is expressed to Joe Bishop and Jon Blanchard, Florida Department of
Agriculture and Consumer Services, Division of Forestry (Withlacoochee District) and
to Parks Small, Barry Birch and Jim Gibson, Florida Department of Environmental
Protection, Division of Recreation and Parks (Wekiwa Springs Geopark). We thank
King's Landing Canoe Rentals for assistance in sampling Rock Springs Run. This is
Florida Agricultural Experiment Station Journal Series R-05045.

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Florida Entomologist 79(4)


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midae: Ecology, Systematics, Cytology and Physiology. Pergamon Press. Oxford
and New York.
TOKESHI, M. 1995a. Species interactions and community structure, pp 297-338 in P.
D. Armitage, P. S. Cranston, and L. C. V. Pinder [eds.], The Chironomidae: The
biology and ecology of non-biting midges. Chapman and Hall. London.
TOKESHI, M. 1995b. Production Ecology, pp. 269-296 in P. D. Armitage, P. S. Cranston,
and L. C. V. Pinder [eds.], The Chironomidae: The biology and ecology of non
biting midges. Chapman and Hall. London.
TOKESHI, M. 1995c. Life cycles and population dynamics, pp. 225-268 in P. D. Armit
age, P. S. Cranston, and L. C. V. Pinder [eds.], The Chironomidae: The biology
and ecology of non-biting midges. Chapman and Hall. London.
WALSHE, B. M. 1951. The feeding habits of certain chironomid larvae (subfamily Ten
dipedinae). Proc. Zool. Soc. London 121: 63-79.
WEBB, S. D. 1990. Historical Biogeography, pp. 70-102 in R. L. Myers and J. J. Ewel
[eds.], The Ecosystems of Florida University of Central Florida Press. Orlando.
WETZEL, R. G. 1983. Limnology 2nd Ed. Saunders College Publishing. Philadelphia
and New York.
WIEDERHOLM, T. [ed.]. 1989. Chironomidae of the Holoarctic Region. Keys and Diag
noses. Part 3. Adult Males. Entomol. Scandinavica Suppl. 34.


December, 1996

















Lobinske et al.: Hexagenia limbata Life History


LIFE HISTORY AND PRODUCTIVITY OF HEXAGENIA
LIMBATA (EPHEMEROPTERA: EPHEMERIDAE) AND
SELECTED PHYSICO-CHEMICAL PARAMETERS IN TWO
TRIBUTARIES OF THE WEKIVA RIVER, CENTRAL FLORIDA

RICHARD J. LOBINSKE'.2, ARSHAD ALI' AND I. JACK STOUT2
1University of Florida, Institute of Food and Agricultural Sciences
Central Florida Research and Education Center, 2700 East Celery Ave.
Sanford, FL 32771

University of Central Florida, Department of Biology, 4000 Central Florida Blvd.
Orlando, FL 32816

ABSTRACT

Nymphal densities and size frequency distribution of Hexagenia limbata (Ser
ville), a burrowing mayfly, were determined monthly for two years in two tributaries
of the Wekiva River, central Florida, along with selected physico-chemical water pa
rameters. Blackwater Creek supported a mean number of 112 (range 0-434) and Rock
Springs Run 89 nymphs per m2 (range 11-258). The mayfly species displayed a univol
tine life history with adult emergence peaking in August. Productivity in Blackwater
Creek was estimated at 4.688 g per m2 and in Rock Springs Run at 3.123 g per m2. Pro
ductivity/biomass ratios were estimated at 4.09 and 4.59 in Blackwater Creek and
Rock Springs Run, respectively. The nymphal densities in both streams were posi
tively correlated with water pH and negatively correlated with water volume. Appar
ently, water volume was the overriding abiotic factor in both streams, influencing
several measured water parameters and as well as nymphal populations during the
study period.

Key Words: Mayfly, life history, streams, size frequency distribution, physico-chemical
parameters, productivity

RESUME

Las densidades ninfales y la distribuci6n de frecuencia de tamano de la efimera
Hexagenia limbata (Serville), asi como parametros fisico-quimicos de agua selecciona
dos, fueron determinados mensualmente durante dos anos en dos tributaries del rio
Wekiva, en Florida Central. El arroyo Blackwater tuvo un promedio de 112 (rango 0
434) y Rock Springs Run 89 ninfas por m2 (rango 11-258). Las species de efimeras
mostrtaron un ciclo de vida univoltino con el pico de emergencia de los adults en
Agosto. La productividad del arroyo de Blackwater fue estimada en 4.688 g por m2 y
en Rock Springs Run en 3.123 g por m2. Las tasas de productividad/biomasa fueron es
timadas en 4.09 y 4.59 en los arroyos Blackwater y Rock Springs Run, respective
mente. Las densidades ninfales en ambas corrientes estuvieron positivamente
correlacionadas con el pH del agua y negativamente correlacionadas con el volume
de agua. Aparentemente, el volume de agua fue el factor mas important en ambas
corrientes, influenciando various de los parametros de agua medidos asi como las po
blaciones ninfales durante el period de studio.

















Florida Entomologist 79(4)


Hexagenia limbata (Serville) (Ephemeroptera: Ephemeridae) is one of the most
geographically widespread mayflies in North America. It is found from coast to coast
as well as from Florida to Canada and often constitutes an important part of the mac
robenthos of both lotic and lentic aquatic habitats (Berner & Pescador 1988, Hunt
1953). High densities and productivity rates of mayflies such as H. limbata may con
stitute a significant component of nutrient and energy cycling within their aquatic
habitats and adjacent terrestrial systems. This would be especially true for Florida,
where almost one quarter of the state's land is swamps (Ewel 1990), marshes (Kush
lan 1990), lakes (Brenner et al. 1990) or streams (Nordlie 1990).
Hexagenia limbata has been extensively studied in terms of life history and pro
ductivity, but mostly in the northern part of its ecological range. The present study on
H. limbata was conducted in two tributaries of the Wekiva River, central Florida, to
determine its productivity and life history in peninsular Florida and to elucidate the
effects of selected environmental conditions. Quantitative samples of H. limbata
nymphs were collected monthly from each stream for two years for these purposes. Se
elected physico-chemical parameters in both streams were also measured to determine
any relationships of these parameters with spatial and seasonal changes of H. lim
bata populations.

METHODS AND MATERIALS

The study streams were located in the Wekiva River basin (a part of the St. Johns
River basin), central Florida (Fig. 1). Blackwater Creek is about 40 km long and is a
second order sand bottom stream with both calcareous and swamp-bog stream as
pects (Beck 1965). Rock Springs Run is a first order calcareous stream (Beck 1965)
about 14.5 km long. Water current in both streams varied from 2-50 cm per sec; local
variation in current velocity resulted in substrates which varied from exposed sand to
thick deposits of detritus and silt.
For sampling H. limbata nymphs and for measuring selected physico-chemical pa
rameters, 10 sampling stations were selected in each stream. These stations were ap
proximately 400 m apart in Blackwater Creek and 1200 m apart in Rock Spring Run.
The exact locations of the sampling stations were determined by coordinates using a
Panasonic model LX-G5500 Global Positioning System receiver (Panasonic Company,
Secaucus, NJ). Each stream was sampled on a monthly basis from February 1993 to
January 1995. Samples were collected between 0830 and 1230 hours local time each
sample day
Selected physical and chemical parameters were measured in situ close to the sed
iment-water interface at, or very near, each sampling station with portable meters or
appropriate field kits. The parameters included: current velocity, water pH, dissolved
oxygen, turbidity, nitrate-N, conductivity, water temperature and secchi disk trans
parency. Water volume in the streams was estimated using mean water elevation
(Blackwater Creek) or cumulative rainfall (Rock Springs Run) for 30 days previous to
a sampling date. Details concerning the various meters, field kits, determination of
water volume and data handling were presented in Lobinske et al. (1996).
For quantitative sampling of H. limbata, one benthic sample was collected from
each station with a 15 x 15 x 15 cm Ekman dredge mounted on a 1.5 m steel pole
(APHA 1992). Samples were washed immediately using a sieve bucket with a 350 pm
pore screen and the collected material appropriately labeled and stored on ice until re
turned to the laboratory.
All collected samples were examined and analyzed within 48 hours. The mayfly
nymphs were identified to species using the keys of Berner & Pescador (1988) and
length of each determined to the nearest mm under 2-40X magnification. Wet weight


December, 1996
















Lobinske et al.: Hexagenia limbata Life History


6 *1 1 I* *
0 1 23 45
Kilometers

St. Johns River



Sulfur Run f


Rock


Little Wekiva River


Wekiwa Springs


Fig. 1. Map of the Wekiva River Basin, central Florida, with Blackwater Creek and
Rock Springs Run study areas marked by boxes. Relative location of the general study
area is marked on outline map of Florida.

of nymphs was determined from length using the formula of Heise et al. (1988) and
dry weight determined using the formula of Hudson & Swanson (1972). Productivity
was estimated using the size-frequency method (Hynes & Coleman 1968, Hamilton
1969). Voucher specimens were deposited with the University of Central Florida Col
election of Arthropods, Orlando, FL, and with the Florida State Collection of Arthro

















Florida Entomologist 79(4)


pods, Florida Department of Agriculture and Consumer Services, Division of Plant
Industry, Gainesville, FL.
Statistical analysis of collected nymphal and physico-chemical data and their
graphical presentation were made by utilizing Instat V. 2.04 (Graphpad Software,
Inc., San Diego, CA) and SlideWrite Plus V. 6.0 (Advanced Graphics Software, Inc.,
Carlsbad, CA). Where needed, data were transformed using log (n+1) transformation
to improve homoscedasticity

RESULTS

Overall density of H. limbata nymphs in Blackwater Creek was 112 per m2 and in
Rock Springs Run 89 per m2 for the 2-year study period. The density difference be
tween the two habitats was statistically not significant (P>0.05). Trends of nymphal
populations in each stream are summarized in Fig. 2. In Blackwater Creek, maxima
(434 nymphs per m2) were taken in September 1993, while the highest nymphal den
sity in Rock Springs Run (258 per m2) occurred in January 1994. Monthly densities
ranged from 11-258 nymphs per m2 in the latter habitat and from 0-434 nymphs per
m2 in the former. Heavy summer rains and Tropical Storm Gordon in November 1994
caused excessive flooding which seemed to have a decimating effect on H. limbata
populations, especially in Blackwater Creek where no nymphs occurred in the Janu
ary 1995 samples. Monthly size frequency distribution of H. limbata nymphs in the
two streams (Fig. 3) reveals a univoltine life cycle with peak emergence occurring in
mid-August. Productivity estimates of H. limbata in Blackwater Creek amounted to
4.688 g per m2 and 3.123 g per m2 in Rock Springs Run. Mean dry biomass was esti
mated at 1.146 g per m2 for Blackwater Creek and 0.681 g per m2 for Rock Springs
Run. The productivity/biomass (P/B) ratios of H. limbatawere 4.09 and 4.59 for Black
water Creek and Rock Springs Run, respectively.
Trends of selected physico-chemical parameters in each habitat during the study
period are shown in Fig. 4. Relationship of these parameters with the nymphal popu
lations examined by linear correlation analysis showed some significant relationships:
For example, water pH (r=0.62, P<0.01, n=23 for Blackwater Creek and r=0.61, P<0.01,
n=23 for Rock Springs Run), nitrate-N (r-0.63, P<0.01, n=21 for Blackwater Creek and
r=0.54, P<0.05, n=20 for Rock Springs Run) and water volume (r-0.60, P<0.01, n=24
for Blackwater Creek 30-day mean water elevation andr=-0.62, P<0.01, n=24 for Rock
Springs Run 30-day cumulative rainfall). No significant correlations were found be
tween nymphal populations and the other physico-chemical parameters shown in Fig.
4. Combined nymphal data from both streams also showed significant correlations with
combined water pH values (r=0.59, P<0.0001, n=46) but not with nitrate-N (P>0.05);
water elevation for Blackwater Creek and rainfall data for Rock Springs Run were not
possible to combine for the cumulative (combined) effect analysis.

DISCUSSION

The univoltine life cycle of H. limbata determined in the present study is in com
plete agreement with the previous observations noted by Berner & Pescador (1988) in
Florida, as is the emergence peak in August. The mean densities of H. limbata in
Blackwater Creek and Rock Springs Run are compatible with H. limbata density re
ports of 41 to 153 per m2 for Lewis and Clark Lake, South Dakota/Nebraska (Swanson
1967), and for South Indian Lake (20-130 per m2), Manitoba, Canada (Giberson &
Rosenberg 1994). However, some streams in the Eglin Air Force Base Reservation in
north Florida had supported <14 H. limbata nymphs per m2 (Scheiring et al. 1981,
Scheiring & Crews 1983).


December, 1996

















Lobinske et al.: Hexagenia limbata Life History


BLACKWATER CREEK


FMAMJ J ASONDJ FMAMJ JASON J


ROCK SPRINGS RUN


FMAMJ JASOND J F MAMJ JASON D J

Fig. 2. Monthly mean population trends of Hexagenia limbata nymphs in Black
water Creek and Rock Springs Run, central Florida (February 1993 to January 1995).


The H. limbata productivity rates of 4.688 g per m2 in Blackwater Creek and 3.123
g per m2 in Rock Springs Run were much higher than the 0.8 g dry wt per m2 measured
by the size frequency method in Savanne Lake, Ontario, Canada (Riklik & Momot
1982), 1.667 g dry wt per m2 in Lewis and Clark Lake (Hudson & Swanson 1972), and
<1.8 g dry wt per m2 (determined from <13 g wet wt per m2) in Dauphin Lake, Mani
toba, Canada (Heise et al. 1988). The resulting P/B ratios of H. limbata were also



















Florida Entomologist 79(4)


BLACKWATER CREEK


FE. 193


__--___---___----
u LM M I4II



SAPR. 193 APR. 11





-------
SAY. 1993 MY. 114



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- 10 JUL 9J3 IJL 1B4
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December, 1996


ROCK SPRINGS RUN

FB.1M FB.IAW



M.I lM liOU. 14





AFim IAm. 1I0
Bo-











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SEP.M I SEPR Il



OCT.f OCT.1994









L I.lIM JAIl I
111111I i W


<5 11 1 7110 3 4 1 3 11 1 i 23i U 2I s 4 11 417 a23 4 11 i411 233292
SIZE CLASS (MM)

Fig. 3. Monthly size frequency distribution of Hexagenia limbata nymphs in Black
water Creek and Rock Springs Run, central Florida (February 1993 to January 1995).



higher in the present study than the values of 2.6 (Riklik & Momot 1982) and 1.68 to
2.38 (Heise etal. 1988) reported from some northern habitats, although a higher value
of 5.7 (P/B ratio) was reported by Smock etal. (1985) for Cedar Creek, South Carolina.
The warmer water temperatures in the investigated streams is probably conducive to
more rapid development of H. limbata, as also shown experimentally by Fremling
(1967) and Giberson & Rosenberg (1992).
























Lobinske et al.: Hexagenia limbata Life History


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Florida Entomologist 79(4)


The significant relationships between H. limbata density and certain water pa
rameters were probably influenced by variations in water volume in the streams. The
inverse relationship between water elevation or rainfall and H. limbata populations
may be due to a direct flushing effect or due to an indirect effect through other water
parameters influenced by high water discharge. The positive correlations of H. lim
bata with nitrate-N seem to be coincidental, since this was not true for combined data
from both streams. The significant correlations with water pH, for each stream and
both combined, indicate a valid pH effect on nymphal density. The pH range (6.20-7.89
for Blackwater Creek and 6.89-7.98 for Rock Springs Run) at which H. limbata oc
curred in the study streams is in agreement with the water pH range of 6.0-7.9 for this
species reported by Roback (1974).
This study provides an initial database on the life history and productivity of H.
limbata in small lotic systems of peninsular Florida. This mayfly is an important com
ponent of the ecosystems studied. Using a hypothetical 5 m width, H. limbata s an
nual production for Blackwater Creek would be 937.6 kg dry wt and 226.4 kg dry wt
for Rock Springs Run. This, combined with the high P/B ratios, indicate that this may
fly contributes greatly to nutrient cycling and energy flow within these streams and
to adjacent terrestrial systems.


ACKNOWLEDGMENTS

Gratitude is expressed to Joe Bishop and Jon Blanchard, Florida Department of
Agriculture, Division of Forestry (Withlacoochee District), and to Parks Small, Barry
Birch and Jim Gibson, Florida Department of Environmental Protection, Division of
Parks and Recreation (Wekiwa Springs Geopark) for their cooperation and assistance
in the field. We thank King's Landing Canoe Rentals for assistance in sampling Rock
Springs Run. This is Florida Agricultural Station Journal Series R-05084.


LITERATURE CITED

APHA. 1992. Standard Methods for the Examination of Water and Wastewater. 18th
Ed. American Public Health Association. Washington, D. C.
BECK, W. M., JR. 1965. The streams of Florida. Bull. Florida State Mus. 10: 91-126.
BERNER, L., AND M. L. PESCADOR 1988. The Mayflies of Florida. University Presses
of Florida. Tallahassee and Gainesville.
BRENNER, M., M. W. BINFORD, AND E. S. DEEVEY. 1990. Lakes, pp. 324-391 in R. L.
Myers and J. J. Ewel [eds.], The Ecosystems of Florida. University of Central
Florida Press. Orlando.
EWEL, K. C. 1990. Swamps, pp. 281 323 in R. L. Myers and J. J. Ewel [eds.], The Eco
systems of Florida. University of Central Florida Press. Orlando.
FREMLING, C. R. 1967. Methods for mass-rearing Hexagenia mayflies
(Ephemeroptera: Ephemeridae). Trans. American Fish. Soc. 96: 407-410.
GIBERSON, D. J., AND D. M. ROSENBERG. 1992. Effects of temperature, food quantity,
and nymphal rearing density on life-history traits of a northern population of
Hexagenia (Ephemeroptera: Ephemeridae). J. N. American Benth. Soc. 11: 181
193.
GIBERSON, D. J., AND D. M. ROSENBERG. 1994. Life histories of burrowing mayflies
(Hexagenia limbata and H. rigida, Ephemeroptera, Ephemeridae) in a north
ern Canadian reservoir. Freshwater Biol. 32: 501-518.
HAMILTON, A. L. 1969. On estimating annual production. Limnol. Oceanog. 14: 771
782.
HEISE, B. A., J. F. FLANNAGAN, AND T. D. GALLOWAY. 1988. Production of Hexagenia
limbata (Serville) and Ephemera simulans Walker (Ephemeroptera) in Dau


December, 1996

















Lobinske et al.: Hexagenia limbata Life History


phin Lake, Manitoba, with a note on weight loss due to preservatives. Cana
dian J. Fish. and Aquat. Sci. 45: 774-781.
HUDSON, P. L., AND G. A. SWANSON. 1972. Production and standing crop of Hexagenia
(Ephemeroptera) in a large reservoir. Stud. Nat. Sci. 1: 142.
HUNT, B. P. 1953. The life history and economic importance of a burrowing mayfly,
Hexagenia limbata, in southern Michigan Lakes. Michigan Department of Con
servation, Bull. Inst. Fish. Res., No. 4. 151 pp.
HYNES, H. B. N., AND M. J. COLEMAN. 1968. A simple method of assessing the annual
production of stream benthos. Limnol. Oceanog. 13: 569-573.
KUSHLAN, J. A. 1990. Freshwater Marshes, pp. 324-363 in R. L. Myers and J. J. Ewel
[eds.], The Ecosystems of Florida. University of Central Florida Press. Orlando.
LOBINSKE, R. J., A. ALI, AND I. J. STOUT. 1996. Qualitative and quantitative studies
on Chironomidae (Diptera) and selected physico-chemical parameters in two
tributaries of the Wekiva River, central Florida. Florida Entomol. 79(4): 531
542.
NORDLIE, F. G. 1990. Rivers and Springs, pp. 392-425 in R. L. Myers and J. J. Ewel
[eds.], The Ecosystems of Florida. University of Central Florida Press. Orlando.
RIKLIK, L., AND W. T. MOMOT. 1982. Production ecology of Hexagenia limbata in Sa
vanne Lake, Ontario. Canadian J. Zool. 60: 2317-2323.
ROBACK, S. S. 1974. Insects (Arthropoda: Insecta), pp. 313-376 in C. W. Hart, Jr. and
S. L. Fuller [eds.], Pollution Ecology of Freshwater Insects. Academic Press.
New York and London.
SCHEIRING, J. F., R. C. CREWS, AND S. M. LEFSTAD. 1981. Benthic Macro-Inverte
brates of Rocky Creek, Eglin Air Force Base, Florida. Air Force Armament Lab
oratory, Eglin Air Force Base, FL. AFATL-TR-81 95.
SCHEIRING, J. F., AND R. C. CREWS. 1983. Benthic Macro-Invertebrates of Bull Creek
and Ramer Branch, Eglin AFB Reservation. Air Force Armaments Laboratory,
Eglin Air Force Base, FL. AFATL-TR-83-24.
SMOCK, L. A., E. GILINSKY, AND D. L. STONEBURNER 1985. Macroinvertebrate produce
tion in a southeastern United States Blackwater Stream. Ecology 66: 1491
1503.
SWANSON, G. A. 1967. Factors influencing the distribution and abundance of Hexage
nia nymphs (Ephemeroptera) in a Missouri River reservoir. Ecology 48: 216
225.

















Florida Entomologist 79(4)


OVIPOSITION PREFERENCE OF SPODOPTERA LATIFASCIA
(LEPIDOPTERA: NOCTUIDAE) FOR SORGHUM, MAIZE AND
NON-CROP VEGETATION


HECTOR E. PORTILLO', HENRY N. PITRE2, DAN H. MECKENSTOCK3
AND KEITH L. ANDREWS4
1BASF Agricultural Research Station, 103 BASF Road, Greenville, MS 38701

2Department of Entomology & Plant Pathology
Mississippi Agricultural and Forestry Experiment Station
Mississippi State University, Mississippi State, MS 39762

3Department of Soil and Crop Science, Texas A&M University
College Station, TX 77843

4Panamerican School of Agriculture, P O. Box 93, Tegucigalpa, Honduras


ABSTRACT

Oviposition preferences of Spodoptera latifascia (Walker) (Lepidoptera: Noctu
idae) for sorghum [Sorghum bicolor (L.) Moench (Poaceae)], maize [Zea mays (L.)
(Poaceae)], and various non-crop species were examined in field cage experiments. A
higher percentage (pooled means) of the total number of eggs per plant were laid on
Amaranthus sp. (probably A. hybridus L. or A. viridis L.) (Amaranthaceae) 24%,
maize 32%, and Ixophorus unisetus (Presl.) Schlecht (Poaceae) 26%, than on Ipomoea
sp. [(probably I. purpurea (L.) Jacq.] (Convolvulacea) 2%, Melampodium divaricatum
(Rich. ex pers.) Dc. (Asteraceae) 6%, Portulaca oleracea L. (Portulacaceae) 7%, and
sorghum 3%. Only maize had a significantly higher percentage of the total number of
eggs laid per plant than the other plant species in one of two experiments. Plant
growth stage (seedling vs. older) did not appear to influence oviposition on any of the
plant species tested. Moths exhibited a wide host oviposition range in our cage exper
iments. In contrast, eggs were collected only from Amaranthus sp., I. unisetus, and
maize in the field in southern Honduras, suggesting that S. latifascia oviposition re
sponse in nature may be somewhat restricted to certain non-crop species and maize.
Our data support results from previous investigations revealing the potential benefits
of non-crop host plants in reducing damage by S. latifascia to sorghum and maize in
intercropped production fields during the early growing season in southern Hondu
ras.

Key Words: Spodoptera latifascia, oviposition preference, sorghum, maize, non-crop
plants


RESUME

Las preferencias de ovoposicidn de Spodoptera latisfacia (Walker) (Lepidoptera:
Noctuidae) en sorgo [(Sorghum bicolor (L) Moench (Poaceae)], maiz [Zea mays (L)
Poaceae] y varias species de plants no cultivadas fueron examinadas en experiment
tos de campo enjaulas. Un porcentaje mas alto del numero total de huevos por plant
fue puesto en Amaranthus sp. (probablemente A. hybridus L. o A. viridis L.) (Amaran
thaceae), maiz, e Ixophorus unisetus (Presl.) Schlecht (Poaceae), con medias del 24%,
32% y 26%, respectivamente. En Ipomoea sp. [probablemente I. purpurea (L.) Jack.]


December, 1996

















Portillo et al.: Spodoptera latifascia oviposition


(Convolvulaceae), la media fue del 2%, en Melampodium divaricatum (Rich ex pers.)
Dc. (Asteraceae) del 6%, en Portulaca oleracea L. (Portulacaceae) del 7%, y en sorgo
del 3%. S61o en uno de los dos experiments el maiz tuvo un porcentaje de huevos sig
nificativamente mas alto. El estado de crecimiento (plantula o plant mas vieja) no
pareci6 influenciar la ovoposici6n en ninguna de las species probadas. Las polillas ex
hibieron un amplio rango de hospedantes de ovoposici6n en los experiments enjau
las. Los huevos fueron solo colectados de Amaranthus sp., I. insertus, y maiz en el
campo en el sur de Honduras, sugiriendo que la respuesta de ovoposicion de S. latis
facia en la naturaleza debe estar restringida a ciertas species no cultivadas y al
maiz. Los datos apoyan los resultados de investigaciones previas revelando el poten
cial benenficioso de las plants hospedantes no cultivadas en la reduccidn del dano al
sorgo y al maiz en la producci6n de campos intercosechados durante la estaci6n tem-
prana en el sur de Honduras.





The armyworm, Spodoptera latifascia (Walker), is an important insect pest of sor
ghum [Sorghum bicolor (L.) Moench (Poaceae)] and maize [Zea mays (L.) (Poaceae)]
seedlings in southern Honduras (Pitre 1988). This species, along with others in an in
sect pest complex including S. frugiperda (J. E. Smith) and Metaponpneumata rogen
hoferi (Moschler), can cause sorghum and maize seedling losses as high as 27% during
the first three weeks of crop growth (Portillo et al. 1994).
S. latifascia is a polyphagous species, the larvae of which are reported to feed on
and cause economic damage to cowpea, soybean, cotton, and young eucalyptus trees
in Brazil (Silva & Magalhaes 1980, Santos et al. 1980, Habib et al. 1983) and many
other crops in Honduras (Howell 1980, Passoa 1983) and Barbados (Ingram 1978).
Population dynamics studies of the langosta complex in southern Honduras revealed
that S. latifascia and M. rogenhoferi caused damage to sorghum and maize early in
the growing season; however, larvae were not found on sorghum or maize at other
times (Portillo et al. 1991). Results from the same study showed that S. latifascia lar
vae occurred in higher numbers on sorghum and maize in areas with weed control
than in areas with weeds.
The reasons for the sudden appearance and disappearance of S. latifascia and M
rogenhoferi from intercropped sorghum and maize fields in southern Honduras have
not been elucidated. There is insufficient evidence to suggest that predators and par
asitoids are responsible for the sudden disappearance of these two species (Portillo
1991). Laboratory feeding performance studies with S. latifascia indicated that some
broadleaf non-crop species common to southern Honduras were better hosts than sor
ghum or maize (Portillo 1991, 1994) and, furthermore, plant host phenology (seedling
versus older plants) significantly affected its biology. Laboratory studies showed that
non-crop plants were preferred by S. latifascia immatures over sorghum and maize,
and it was suggested that non-crop vegetation, particularly broadleaf weeds, in pro
duction fields may reduce crop damage by attracting larvae of this insect pest and
serving as hosts (Portillo et al. 1996). However, knowledge of the relative oviposition
preferences of this insect is lacking.
The objective of this study was to determine oviposition preferences of S. latifascia
for seedling (representing plant growth stages at the beginning of the season, e.g.,
when S. latifascia population peaks) and older plants (representing advanced plant
growth stages as they would appear later in the growing season, e.g., when S. latifas
cia population declines) of sorghum, maize, and five common non-crop plant species
present during the growing season in southern Honduras.

















Florida Entomologist 79(4)


MATERIALS AND METHODS

Adult Fecundity and Mortality
Information on the reproductive behavior of S. latifascia females is limited or un
available. Therefore, a preliminary study was conducted to obtain data on oviposition
patterns and adult mortality. This information served as a guide for selection of moths
of specific ages to be used in oviposition preference experiments.
A laboratory colony was initiated with 208 third and fourth-instar larvae col
elected in a maize field at El Conchal on the coastal plains (coordinates ca. 13'31' N,
87'43' W, at sea level) in the Department of Valle in southern Honduras in early to
mid-May, 1990. Newly emerged females (n=25) from the first laboratory generation
were placed individually in paper bags (13 x 8 x 27.3 cm) containing a single one to
two-day-old male and a honey-water food source (Portillo & Pitre 1992). Moths were
held at 24+5'C and 12:12 [L:D] photoperiod. Males were removed after 3 nights. Eggs
laid (masses) in the bags were counted every 2 to 3 days, at which time the female was
provided with a new bag and fresh food.

Cage Experiments

Four experiments were conducted in field cages during 1991 and 1992 at Zamo
rano, Honduras. Plant species common to southern Honduras, where S. latifascia lar
vae had been collected, were selected for the experiments. These species were also
present in the area around Zamorano. Plant species tested included sorghum, maize,
Ixophorus unisetus (Presl.) Schlecht (Poaceae) (the most prevalent grass species on
the coastal plains in southern Honduras), and four common non-crop broadleaf spe
cies that commonly inhabit production fields in southern Honduras. The broadleaf
species included Amaranthus sp. (probably A. hybridus L. or A. viridis L.) (Amaran
thaceae), Portulaca oleracea L. (Portulacaceae), Ipomoea sp. [(probably I. purpurea
(L.) Jacq.] (Convolvulaceae), and Melampodium divaricatum (Rich. ex pers.) Dc.
(Asteraceae). Two phenological growth stages, seedlings (2-4 leaves unfolded for grass
plants and 2-6 true leaves or leaf pairs unfolded for broadleaf plants which repre
sented the growth stage of crops and/or surrounding non-crop vegetation 1-3 weeks
after crops were planted, as well as the time when the S. latifascia population peaked)
and older plants (5-8 leaves unfolded for grass plants and from 9 true leaves or leaf
pairs unfolded to full bloom for broadleaf plants which represented the growth stage
of crops and/or surrounding non-crop vegetation 4-6 weeks after crops were planted,
and the time when the S. latifascia population declined) were included for each plant
species in experiments 1 and 2 (1991). Because seedlings of some species were not
available when plants were collected in the field, only one stage (4-6 leaves unfolded
for grass plants and 6-9 true leaves or leaf pairs unfolded for broadleaf plants) was in
cluded in experiments 3 and 4 (1992). To obtain plants at the desired test growth
stages, non-crop plant species in earlier growth stages than those desired for testing
were transplanted from the field into pots (11.5 cm diam and 25.5 cm height) and were
held in wet soil in a shade house for 2-4 days until they recovered from the stress
caused by transplanting. Sorghum and maize plants were obtained from staggered
plantings of landrace sorghum and maize (seeds obtained from farmers in southern
Honduras) in pots in the greenhouse. In Experiments 1 and 2, the test design was a
factorial with randomized complete blocks; factors included plant species (n=7) and
plant growth stages (n=2). In Experiments 3 and 4 the test design included only plant
species as treatments in a randomized complete block. A total of six (Experiments 1
and 2) and five (Experiments 3 and 4) plants were included per test species and
growth stage in each of 6 and 5 replications in Experiments 1 and 2, and Experiments


December, 1996

















Portillo et al.: Spodoptera latifascia oviposition


3 and 4, respectively. Potted plants were placed inside 1.8 x 1.8 x 1.8 m saran screen
cages (Chicopee Mfg. Co., Gainesville, GA 30503) set up in the field. Plants of each
species were placed in rows in a randomized complete block design, with growth
stages (Experiments 1 and 2) of each species placed side-by-side (Fig. 1).
The insect test colony for Experiments 1 and 2 was initiated with 295 third and
fourth-instar larvae collected from a maize field near El Conchal in late May, 1991.
Second laboratory generation adults from this field population were used in the ex
periment. A second colony was initiated with 194 third-and fourth-instar larvae col
elected in early June, 1992 from a maize field in the same location as in 1991, and
second laboratory generation adults of this colony were used for Experiments 3 and 4.
Newly emerged moths were placed in paper bags as described above, with each bag
containing two females and one male. Males were allowed to remain in the bags for
three nights. A mating success of 84% was achieved using this technique (as observed
in the adult fecundity and mortality study described above). Bags were held at 236C
(Experiments 1 and 2) and 226C (Experiments 3 and 4) and 12:12 [L:D] photoperiod
until females were seven-to-eight days old. Females were released into the saran
screen cages in the field for oviposition on the test plants between 1600-1700 hours.
Three replications (1 cage each) were used in Experiments 1 and 2. Fifteen seven-day
old females were released into each of three replications in Experiment 1 and 28
eight-day-old females in each of three replications in Experiment 2. A 30% honeywa
ter food source was made available to the moths by placing cotton balls soaked with
the honey solution inside a 30 ml plastic cup. Cups were hung at a height of about 1
m above the soil on the inside walls of the cages (2 per side) by hooking the cups to the
screen with paper clips. Females remained in the cages for 3 nights after which time
the cages were opened to flush the moths. Plants were removed from the cages and
searched for egg masses. Leaves with egg masses were removed from the plants and
the number of eggs per mass were counted under a stereoscope in the laboratory.
Moths were released in Experiment 1 on 15 July. On 19 July plants used in the first
experiment were returned to the cages (using test design described above) and moths
were released into the cages for Experiment 2. Moth ovipositional behavior bias due
to possible chemical markers on previously used test plants may have been minimal
because of the removal of egg masses along with the leaves on which they were laid.
Ambient conditions for both experiments were 23+7'C and 12:12 [L:D] photoperiod.
In Experiment 3, two replications were included in one cage in which 75 seven
day-old females were released on 31 July and confined for 3 nights. In Experiment 4
three replications were conducted (one per cage) and 38 seven-day-old females were
released in each cage on 3 August. Eggs in Experiment 4 had to be removed after two
nights instead of three to avoid losing the replications to rain expected on the third
night. In Experiment 1, moths laid a considerable number of egg masses on the cage
screen. Therefore, to compensate for egg masses laid on the screen instead of on the
plants, the number of moths released per cage was increased in the following experi
ments. Plants and experimental procedures utilized were as described for Experi
ments 1 and 2. Experiments were conducted at 22+7'C and 12:12 [L:D] photoperiod.
The average percentage of the total number of eggs laid per plant on each plant spe
cies and growth stage was analyzed by ANOVA and means were separated by Tukey's
HSD Method (SAS Institute 1985). Percent data were subjected to arcsin square root
transformation before analysis (Steel & Torrie 1980).

Field Observations

Crop and non-crop plants in and around intercropped sorghum and maize produce
tion fields on the coastal plains in southern Honduras were sampled for S. latifascia












Florida Entomologist 79(4)


_____ 1.8 m



Plant Species 1

00000000000000
000 0000000000
1 00000000000000
S00000000000O000
00000000000000
00000000000000

t l 2 3 4 5 6 7
Older
Seedling


< 1.8 m






0000000
1. 0000000
0000000
0000000
0000000
2 3 4 5 6 7

Plant Species I

Fig. 1. Field cage experimental layout of treatments (plant species/growth stage)
in oviposition preference experiments with Spodoptera latifascia. Panamerican
School of Agriculture, Zamorano, Honduras. Experiments 1 and 2 (top), Experiments
3 and 4 (bottom). Rows with the different plant species were randomized in each rep
location.


December, 1996

















Portillo et al.: Spodoptera latifascia oviposition


eggs in 1990, 1991, and 1992. Samples were not taken in the foothills (same coordi
nates as the plains but 52 m above sea level) because the density of non-crop species
was too low for comparisons to be made among species at the time this insect was a
problem in production fields. Plant species selected for the cage experiments were
given most attention in the sampling process. One hundred plants of each of the test
species were examined for S. latifascia egg masses in three fields during a three-week
period in June 1990. In 1991, 200 plants of each test species were sampled in each of
four fields during a 5-day period in mid-to-late May (May 17-21). In 1992, one hundred
plants of each test species were examined in each of four fields in June (June 9-11).
Egg masses collected were placed in 29.6 ml plastic cups filled with 2 ml of agar in the
bottom and transported to the laboratory. The egg masses then were placed in petri
dishes (1 egg mass per dish) with a damp paper towel in the bottom and identified by
source of collection. Neonate larvae were fed pinto bean artificial diet (Perkins 1979)
until attaining a size appropriate for species identification. Statistical analysis was
not performed on the data because of unequal densities of plant species in the crop
production areas. Thus, data are presented as collected for discussion.


RESULTS


Adult Fecundity and Mortality

In the preliminary study four females did not lay fertile eggs, therefore data from
these moths were excluded. An oviposition peak occurred on the seventh day after
moth emergence (Table 1). After a reduction in the number of eggs laid per moth from
days 9 to 13 following emergence, a second oviposition peak was observed 16 days af
ter moth emergence followed by a rapid decline in fecundity (Table 1). In studies with
a related species, S. frugiperda (J. E. Smith), Simmons & Rogers (1994) collected data
that showed two fecundity peaks (about 4 and 8 days after moth emergence) through
out the lifespan of female moths, with a sharp decline after the second peak. In our
study moth mortality began and rapidly increased after the second oviposition peak.
The second peak in oviposition observed in our study, and in fecundity observed by


TABLE 1. FECUNDITY AND MORTALITY OF SPODOPTERA LATIFASCIA FEMALES IN THE
LABORATORY.

No. Eggs Laid/Moth
Days After Moth Emergence (MeanSD) n % Mortality

4 136+349 21 0
7 504+1175 21 0
9 324+489 21 0
11 310+485 21 0
13 309+372 21 0
16 807+698 19 24
18 272+340 12 52
20 341+397 8 67
23 324+261 7 81
25 20+37 5 100

















Florida Entomologist 79(4)


Simmons & Rogers (1994), may be viewed as a result of a survival instinct through
which aging moths invest their last resources into reproduction. Female moths in our
study had an average longevity of 223 days. Habib et al. (1983) reported that S. lat
ifascia female moths held at 27+5'C had average (range) longevities of 13+1 (6-19)
and 121 (10-22) days when larvae were reared on cotton and soybean, respectively.
The lower average temperature (245C) at which moths were held in our study, and
a different larval host may have caused an increase in their average longevity A sig
nificant increase in Heliothis virescens (F) female moth longevity with a decrease in
temperature, moths living as long as 37+3 days when held at 15.6C, was reported by
Henneberry & Clayton (1991). In addition to this temperature effect, Nadgauda & Pi
tre (1983) reported significant differences in H. virescens female moth longevity when
larvae of this insect were reared on soybean, cotton or artificial diet. Based on these
preliminary results of S. latifascia female moth fecundity and longevity, 7 to 8 day-old
moths were selected for the oviposition preference experiments.


Cage and Field Oviposition Preference

S. latifascia moths laid eggs on only maize, Amaranthus sp., and I unisetus in Ex
periments 1 and 2 (Table 2). In contrast, eggs were laid on all test plant species in Ex
periments 3 and 4. A greater percentage of the total number of eggs were laid on
maize and I. unisetus than on the other test host plants. In Experiments 1 and 2, there
was no significant interaction between plant species and plant growth stage (F=0.67;
df=6; P=0.68 and F=0.57; df=6; P=0.75, respectively), and plant growth stage did not
influence the oviposition response of the moths (F=0.15; df=1; P=0.70 and F=0.59;
df=1; P=0.45). The ovipositional response of S. latifascia showed only a marginally
significant difference among the plant species in Experiment 1 (F=2.44; df=6;
P=0.053) but was significantly different in Experiment 2 (F 3.21; df=6; P=0.0169);
however, all plant hosts were similarly attractive for oviposition in Experiment 3
(F 0.56; df=6; P=0.75) and Experiment 4 (F=0.54; df=6; P=0.77).
A greater number of plants and fewer moths were used per replication in Experi
ments 1 and 2 (84 plants and 15-28 moths) than in Experiments 3 and 4 (35 plants
and 38 moths), thus there were fewer moths per plant in Experiments 1 and 2. A re
duction in the number of moths may have resulted in limited oviposition on the less
attractive hosts in Experiments 1 and 2. On the other hand, plant species not receive
ing eggs in Experiments 1 and 2 may have had eggs oviposited by chance in Experi
ments 3 and 4, since the number of moths per plant was increased. Egg masses laid
on the cage screen were not considered in the analysis.
In sampling for S. latifascia eggs in the field in 1990, four egg masses were found
on Amaranthus sp., two on maize, and one on I. unisetus. In 1991, one egg mass was
found on I. unisetus, five on maize, and none on other broadleaf species. S. latifascia
egg masses were not found on any of the plant species searched in 1992.


DISCUSSION

Previous larval feeding preference studies indicated that the same broadleaf spe
cies tested in this study were preferred by S. latifascia larvae over sorghum and maize
(Portillo et al. 1996). Furthermore, larval developmental performance studies indi
cated that the same broadleaf species were suitable hosts for S. latifascia develop
ment (Portillo 1994). Sorghum, maize, and the grass I. unisetus were viewed as poor
hosts and/or did not sustain S. latifascia larval growth, development, or ultimately re
production (Portillo 1994). However, in the present study S. latifascia moths showed


December, 1996






















Portillo et al.: Spodoptera latifascia oviposition


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Florida Entomologist 79(4)


similar oviposition preferences for maize as well as for the non-crop species Amaran
thus sp. and I. unisetus, thus, indicating that S. latifascia may not be very selective in
choosing a host for oviposition. The imperfect relationship between oviposition pref
erence for specific plant species and developmental performance of offspring on these
plants has been considered problematical in the theory of insect/plant interactions
(Wiklund 1974, Thompson 1988). Adult oviposition preference for and larval develop
mental performance on some plant species has been observed to have a close relation
ship (Singer et al. 1988). However, this favorable relationship between oviposition
preference and larval developmental performance was not observed in pierid butter
flies by Courtney (1981) or in Papilio machaon L. by Wiklund (1974). Although adults
used in our study were reared on pinto bean diet rather than on any of the hosts
tested, one might expect that adults would not consistently choose, as ovipositional
hosts, plants (i.e., maize and I. unisetus) that are fatal or at least not wholesome to the
immature stages. A review of the genetic covariance in preference and developmental
performance by Thompson (1988) indicated that these biological parameters can vary
either together or independently. The insect may have a wide host range for oviposi
tion, but satisfactory developmental performance may be limited to certain hosts,
which seems to occur with S. latifascia. It has been suggested that oviposition prefer
ence for a new host plant species may evolve before developmental physiology (of lar
vae) if the insect is exposed to abundant novel hosts (i.e., sorghum and maize in this
case) (Futuyma 1983).
Oviposition on I unisetus and Amaranthus sp. occurred at about the same fre
quency (percent of total eggs laid per plant) as on maize, and oviposition on the other
broadleaf species was similar to that on sorghum in the cage experiments, indicating
that non-crop species in production fields may be attractive for oviposition by S. lati
fascia females. With larvae preferring to feed on some non-crop species when com
pared with sorghum and maize, there should be an overall reduction in damage to the
crops if these hosts are abundant. Thus, weed management practices which promote
abundance of those species should contribute to lower insect damage to sorghum and
maize (Portillo 1994).
Since S. latifascia appears to have only one damaging generation annually on sor
ghum and maize in southern Honduras, the value of controlling the pest population
on non-crop plants is questionable. Agricultural practices in the sorghum and maize
agroecosystems in southern Honduras include limited weed control because most
farmers do not use chemical herbicides. However, the use of tractors and ox-pulled
plows in the preparation of fields for planting on the coastal plains and the slash and
burn practices in the foothills usually create conditions where crop emergence occurs
at the time when non-crop plants may not be present. These conditions usually are as
sociated with high insect damage to sorghum and maize, especially in the foothills.
Farmers who do not have money to purchase insecticides in areas where S. latifascia
and related species in the pest complex are limiting sorghum and maize production
might be advised to synchronize crop planting with emergence and establishment of
non-crop plants in fields prepared for planting. However, the implementation of this
practice may be difficult in most areas in southern Honduras where farmers are urged
to plant with the onset of rains in order to ensure seed germination and stand estab
lishment and reduce the probability of drought stress to crops as the season
progresses. Studies on the effects of delayed planting date on crop establishment and
yield are needed to elucidate the impact of this practice. Also, the impact of interspe
cific competition between weeds and crop plants on crop yield compared with the in
jury losses by insects during the growing season in delayed plantings needs
elucidation. A literature review by Andow (1991) indicated that net yield gains in
fields intermingled with weeds occurred only rarely and only when losses to insect in


December, 1996

















Portillo et al.: Spodoptera latifascia oviposition


jury were severe in monoculture. Severe crop damage by S. latifascia and other spe
cies in the pest complex is observed often in southern Honduras; thus, the benefit of
weeds in reducing pest damage to crops is likely to outweigh any reduction in crop
yield due to weed competition. However, the nature of these relationships needs fur
their investigation. Additionally, ovipositional preference studies with S. latifascia
and other species in this pest complex under field conditions are needed to confirm our
results.


ACKNOWLEDGMENTS

The authors thank Antonio Molina, botanist, Panamerican School of Agriculture,
Zamorano, Honduras for plant identifications and R. Brown, F Davis and J. Todd for
their comments on the manuscript. The research was supported in part by the govern
ment of Honduras, The United States Agency for International Development (US
AID), through the PL 480 Title I Program Agreement, the International Sorghum and
Millet Collaborative Research Support Program (INTSORMIL), USAID development
grant DAN 1254-G-00-0021-00, and Project Manejo Integrado de Plagas en Hondu
ras, Escuela Agricola Panamericana (EAP), Tegucigalpa, Honduras. It was conducted
under the memorandum of understanding between the Ministry of Natural Resources
(MNR) of the government of Honduras and INTSORMIL, Acuerdo No. 152, Teg
ucigalpa, D.C., 8 February 1983, and the memorandum of understanding between the
Escuela Agricola Panamericana and INTSORMIL, El Zamorano, 17 October 1988.
Joint contribution of MNR, EAP, Texas A&M University and Mississippi State Uni
versity. This research was conducted in partial fulfillment of requirements for the
Ph.D. degree in the Department of Entomology and Plant Pathology (Project MS
1509). Approved for publication as Journal Article No. J-8791 of the Mississippi Agri
cultural and Forestry Experiment Station, Mississippi State University.


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Environ. Entomol. 20: 1228-1235.
COURTNEY, S. P. 1981. Coevolution of pierid butterflies and their cruciferous host
plants. III. Anthocharis cardamines (L.). Survival, development, and oviposi
tion on different host plants. Oecologia 51: 91 96.
FUTUYMA, D. J. 1983. Selective factors in the evolution of host choice by phytophagous
insects, pp. 227-244 in S. Ahmad [ed.], Herbivorous insects: host-seeking be
havior and mechanisms. Academic Press, New York.
HABIB, M. E. M., L. M. PALEARI, AND M. E. C. AMARAL. 1983. Effect of three larval di
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HENNEBERRY, T. J., AND T. E. CLAYTON. 1991. Tobacco budworm (Lepidoptera: Noc
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HOWELL, H. N. 1980. Notes on the complex of cotton pests in Honduras, C.A.: their
ecology and control. CEIBA 22: 2933.
INGRAM, W. R. 1978. Cotton entomology in Barbados. Progress Report. London, UK.
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NADGAUDA, D., AND H. N. PITRE. 1983. Development, fecundity, and longevity of the
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selectos en Honduras. CEIBA 25:1 97.

















Florida Entomologist 79(4)


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Honduras. M.S. Thesis, Mississippi State University, Mississippi State, MS.
PORTILLO, H. E. 1994. Feeding performance and oviposition preference of Spodoptera
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PORTILLO, H. E., AND H. N. PITRE. 1992. Effect of four soybean genotypes on the de
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PORTILLO, H. E., H. N. PITRE, K. L. ANDREWS, AND D. H. MECKENSTOCK. 1994. The in
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December, 1996

















Tsai & Perrier: Leafhopper Internal Morphology


MORPHOLOGY OF THE DIGESTIVE AND REPRODUCTIVE
SYSTEMS OF DALBULUS MAIDIS AND GRAMINELLA
NIGRIFRONS (HOMOPTERA: CICADELLIDAE)

JAMES H. TSAI AND JOAN L. PERRIER
Fort Lauderdale Research and Education Center, University of Florida, IFAS
3205 College Avenue, Fort Lauderdale, FL 33314

ABSTRACT

The corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Homoptera: Cicadel
lidae) is the principal vector of maize rayado fino marafivirus, corn stunt spiroplasma
and maize bushy stunt phytoplasma in tropical and subtropical areas of the Western
Hemisphere. The black-faced leafhopper, Graminella nigrifrons (Fobes) (Homoptera:
Cicadellidae) is the principal vector of maize chlorotic dwarf waikavirus in North
America. The morphology of their digestive and reproductive systems was studied by
light microscopy, and illustrations were made to aid in dissection and injection of
pathogenic inoculum for various vector-pathogen relation studies. In both species, two
salivary glands, located one on each side of the head, extend into the mesothorax.
Each gland consists of principal and accessory glands. The former contains an ante
rior lobe and posterior lobe. Two types of acini are present in the anterior lobe,
whereas the posterior lobe has four acini. The accessory glands of D. maidis and G. ni
grifrons are very similar rod to elbow-shaped structures. The esophagus of both spe
cies is a narrow tube originating from the pharynx and extending to the anterior
midgut below the filter chamber. The anterior midgut is a large sac-like structure ex
tending from the metathorax through the entire length of the abdomen, and then as
cends backward to the anterior of the midgut to form the filter chamber. The filter
chamber of D. maidis has a more complex structure than that of G. nigrifrons. There
are two pairs of Malpighian tubules in both species. The central tubule is formed from
a pair of fused tubules within the filter chamber; the other tubules extend along the
front of the hindgut. In G. nigrifrons the three tubules run parallel to each other along
the top of the posterior midgut. In D. maidis, the central tubule and one tubule from
the other pair run along the interior of the deep loop of the posterior midgut; the other
tubule runs along the exterior of the loop. The ovaries of both species contain six ova
orioles. Each ovariole consists of a terminal filament, a germarium, developing oocytes
and eggs within follicles and a pedicle. The ovarioles contain six follicles. In G. nigri
frons each ovariole usually contains only one egg within the last follicle whereas the
ovarioles of D. maidis often contain two eggs. The ovarioles open into the lateral ovi
duct, common oviduct and the vagina. The spermathecae open into the common ovi
duct. A collateral gland and accessory glands are present. The male of both species
has two lateral testes each with six follicles. A pair of accessory glands arise at the
posterior of each seminal vesicle and open into the lateral ejaculatory duct.

Key Words: Internal morphology, anatomy, leafhopper, maize, corn stunt spiroplasma,
maize rayado fino marafivirus, maize bushy stunt phytoplasma, maize chlorotic dwarf
waikavirus

RESUME

Dalbulus maidis (DeLong y Wolcott) (Homoptera: Cicadellidae) es el principal vec
tor del marafivirus del rayado fino del maiz, del espiroplasma de la atrofia del maiz y
del fitoplasma de la atrofia ramificada del maiz en areas tropicales y subtropicales del
Hemisferio Occidental. Graminella nigrifrons (Fobes) (Homoptera: Cicadellidae) es el
vector principal del waikavirus del enanismo clor6tico del maiz en Norteam6rica. La
morfologia de sus sitemas digestive y reproductive fue estudiada mediante microsco

















Florida Entomologist 79(4)


pia de luz. Fueron hechas ilustraciones para ayudar la disecci6n y la inyecci6n de in6
culo patog6nico para studios sobre la relaci6n vector-pat6geno. En ambas species,
dos glandulas salivales, localizadas a cada lado de la cabeza, se extienden en el meso
t6rax. Cada glandula consiste de glandulas principles y accesorias. La iltimas con
tienen un 16bulo anterior y un 16bulo posterior. Dos tipos de acini estan presents en
el lobulo anterior, mientras que el 16bulo posterior tiene cuatro acini. Las glandulas
accesorias de D. maidis y G. nigrifrons son muy similares a bastones o a estructuras
en forma de codo. El es6fago de ambas species es un tubo estrecho que se original en
la faringe y se extiende hacia la parte anterior del intestine medio, bajo la camara fil
trante. La parte anterior del intestine medio es una estructura en forma de bolsa que
se extiende a todo lo largo del abdomen, a partir del metat6rax y asciende hacia la
parte anterior del intestine medio para former la camara filtrante. La camara fil
trante de D. maidis tiene una estructura mas compleja que la de G. nigrifrons. Hay
dos pares de tfbulos de Malpighi en ambas species. El tfbulo central esta formado
de un par de tfbulos fundidos dentro de la camara filtrante; los otros tfbulos se ex
tienden a lo largo del intestine posterior. En G. nigirifrons los tres tfbulos corren pa
ralelos a lo largo de la cima del intestine medio. En D. maidis el tfbulo central y un
tubulo del otro par corren a lo largo del interior de la curvatura de la parte posterior
del intestine medio; el otro tfbulo corre a lo largo del exterior de la curvatura. Los ova
rios de ambas species contienen seis ovariolas. Cada ovariola consisite de un fila
mento terminal, el germario, que desarrolla los oocitos y los huevos dentro de los
foliculos, y un pedfnculo. Las ovariolas contienen seis foliculos. En G. nigrifrons cada
ovariola usualmente contiene solo un huevo dentro del iltimo foliculo mientras que
las ovariolas de D. maidis a menudo conienen dos huevos. Las ovariolas se abren en
el oviducto lateral, el oviducto comfn y la vagina. La espermateca se abre dentro del
oviducto comfn. Una glandula collateral y una accesoria estan presents. El macho de
ambas species tiene dos testiculos, cada uno con seis foliculos. Un par de glandulas
accesorias se alza en la parte posterior de cada vesicula seminal y se abre en el con
ducto eyaculatorio lateral.





Maize (Zea mays L.) is the world's most widely grown crop. An average of 380 mil
lion tons are produced annually on 120 million ha in 53 countries in almost all tropical
areas of the world, including tropical highlands over 3000 m in altitude and temper
ate areas as far north as the 65th latitude. Because different ecological conditions ex
ist between the temperate areas and the tropics, disease agents and their insect
vectors also differ. To date, three important maize pathogens, maize rayado fino ma
rafivirus, corn stunt spiroplasma (Spiroplasma kunkelil) and maize bushy stunt phy
toplasma are known to be persistently transmitted by the corn leafhopper, Dalbulus
maidis (DeLong & Wolcott), the principal leafhopper vector in hot and humid tropics
as well as in the southern US (Chen & Liao 1975, Davis & Whorley 1973, Gamez 1973,
Nault & Bradfute 1979, Tsai & Falk 1988). This vector is found abundantly from the
southern US to Argentina (Nault 1980). In temperate areas, maize chlorotic dwarf
waikavirus is most prevalent and is transmitted semipersistently by the blackfaced
leafhopper, Graminella nigrifrons (Forbes) (Nault et al. 1973).
Because of the economic importance of these diseases in the Western Hemisphere,
maize pathogens and their vectors have been the subject of many studies. However,
only a few studies on the location of maize pathogens in various organs and tissues of
Auchenorrhynchous vectors have been conducted using electron microscopy and sero
logical techniques (Ammar 1985, 1987, Ammar & Nault 1985, 1991, Ammar et al.
1994, Childress & Harris 1989, Falk et al. 1988, Herold & Munz 1965, Falk & Tsai
1984, 1985, Nault & Gordon 1988). These studies involved dissections of insects to as
say for virus presence in different organs. Because it is difficult to perform these dis


December, 1996

















Tsai & Perrier: Leafhopper Internal Morphology


sections with accuracy, a guide to the internal morphology was needed. The
information on internal structures of the vectors of maize pathogens is scarce (Ammar
1985, 1986, 1987, Ammar & Nault 1991, Backus 1985, Childress & Harris 1989, Tsai
& Perrier 1993). Accordingly, we initiated this detailed study of the internal morphol
ogy of D. maidis and G. nigrifrons for the purpose of facilitating the study of the fate
of maize pathogens in their vectors.

MATERIALS AND METHODS

Dalbulus maidis was reared in the laboratory on corn, Zea mays L. (var. Saccha
rata "Guardian"). Graminella nigrifrons (Forbes) was reared on a combination of oats
(Avena sativa L.) and sweet corn in a growth room at 24+1'C and constant photope
riod of 12:12 (L:D). Approximately 300 adults of both sexes from both species were dis
sected. Insects were placed in a freezer at 0C for periods of one to two h, then were
dissected in a solution of 60 parts deionized water to 1 part safranin red 1%. The or
gans removed were left in the solution for 60 min, then were rinsed and observed with
a dissecting microscope and a compound microscope at magnifications from 10x to
400x. When stains were not used, the organs were placed on a black background in or
der to observe delicate structures. Observations of other fine structures (the salivary
glands, the filter chamber and its internal structure, the ovarioles, and various other
glands) were performed on cold-anesthetized insects kept at 7.6'C. The dissections
were performed in stain solutions of 120 parts Clarke's solution to 1 part neutral red
0.01% (Sogawa 1965) or 120 parts Clarke's solution to 1 part methelyne blue chloride
0.01%. Some of the finer details could be observed within the salivary glands by using
these stains together.

RESULTS AND DISCUSSION

Digestive System
Salivary glands. The salivary glands of G. nigrifrons and D. maidis, which are
present on each side of the thorax and head (Sg in Figs. 1 and 3), consist of principal
and accessory glands (Pg, Ag in Figs. 5 and 6). The principal gland contains an ante
rior lobe and a posterior lobe (Al, P1 in Figs. 5 and 6). Two types of acini, or follicles
were observed in the anterior lobe, along with a small spherical appendage (I, and Sa
in Fig. 5; I, II and Sa in Fig. 6). The posterior lobe contains four acini (III-VI in Figs.
5 and 6). The I and II cells and the spherical appendage open anteriorly into the prin
cipal salivary duct (I, II, Psd in Figs. 5 and 6); the III through VI cells open posteriorly
into the same duct (Fig. 6; III-VI, Psd). At this juncture the accessory duct (Asd in Fig.
6) joins the principal salivary duct. The two principal ducts unite to form the common
salivary duct (Sd in Fig 6) which extends into the head to the salivary syringe which
in turn opens into the salivary canal in the stylets (Ammar 1985, Backus 1985,
Sogawa 1965). In contrast, in Hecalus lefroyi Dist., these two principal ducts open sep
arately into the salivary syringe (Saxena 1955).
Sogawa (1965) states that the anterior lobe of Cicadellidae usually contain two dis
tinctly different types of bi-nucleate cells; the number, size and shape vary from spe
cies to species. We confirm this conclusion for these two species. The anterior lobe of
D. maidis (Al in Fig. 6) is large and translucent. The distal region, which contains the
I-cells (I in Fig. 6), consists of two to four large ovoid cells with large nuclei. A small
spherical appendage also arises from this region (Sa in Fig. 6). The I-cells emerge from
the center of the II-cells (II in Fig 6). This proximal area usually contains six smaller
cells arranged concentrically. The cytoplasm appears denser than that of the I-cells
and the nuclei are smaller. Both the I and II-acini are often smaller than those illus

















Florida Entomologist 79(4)


treated (I, II in Figs. 5 and 6). The anterior lobe of G. nigrifrons differs from that of D.
maidis in that it usually contains only one acinus type (II in Fig. 5). This acinus is a
tri-lobed group of cells containing one or two cells per lobe (II in Fig. 5)). The spherical
appendage arises from this structure (Sa in Fig. 5). Rarely, another group of cells, sim
ilar to the I-acinus of D. maidis, has been observed.
The posterior lobe of the Cicadellidae described by Sogawa (1965) contains acini
III through VI. These bi-nucleate cells are all arranged concentrically. There are six
III-type cells and varying numbers of IV-, V and VI-type cells. Both D. maidis and G.
nigrifrons have similar posterior lobes (PI in Figs. 5 and 6). The III-, IV, and V type
cells are all six in number. The VI-acinus contains three cells.
The III-type cells in D. maidis are large, translucent, and teardrop-shaped, and
are separate from one another. Their nuclei are large and pronounced (III in Fig. 6).
The rosette shaped IV acinus is the most noticeable in the salivary gland (IV in Fig.
6); the cytoplasm is dense and the large nuclei are faint. Approximately 70% of the IV
acini observed had this amorphous, swollen shape. Other IV type cells were more de
fined and separate from each other. The insects with the more defined IV cells had an
terior lobes that were reduced in size. The six V type cells of D. maidis are much
smaller than the IV type cells with smaller nuclei (V in Fig. 6). This acinus again var
ies in shape ranging from amorphous to well-defined teardrop-shaped cells. The VI
acinus, situated at the center of the V acini (IV in Fig. 6) is small, also tear drop
shaped and contains three indistinct cells.
The posterior lobe of G. nigrifrons is similar to that of D. maidis (PI in Fig. 5). The
III-type cells show no significant variation (III in Fig. 5). The IV acinus, however, is
much less pronounced than that of D. maidis (IV in Fig. 5). Its shape similarly ranges
from amorphous to well-defined cells. Approximately 50% of the G. nigrifrons ob
served had well defined IV type cells. Occasionally these cells had a hardened,
shrunken appearance. The only noticeable difference between the V and VI-acini of
the two insects was the smaller size of the V type cells of G. nigrifrons (V in Fig. 5).
The accessory glands of D. maidis and G. nigrifrons are very similar (Ag in Figs. 5
and 6) and range from rod to elbow-shaped. The size of the gland and the length of
the accessory salivary duct (Asg in Figs. 5 and 6) vary within species. The variation
in numbers and morphology of acini could be due to the age of the insect or to physi
logical factors. Because numerous fat bodies fill the head and surround the salivary
glands, it is sometimes difficult to separate the smaller and more translucent acini
from the fat bodies. In Nephotettix cincticeps Uhler, the principal gland has at least
five lobes and five cell types (I-V) (Nasu 1965) whereas only four lobes and four cell
types were reported in the principal gland of Empoasca fabae (Harris) (Berlin &
Hibbs 1963). Gil-Fernandez & Black (1965) reported that Agallia constricta (Van
Duzee) had four lobes and five acini in its principal gland. As many as 21 acini have
been observed in the principal gland of Cicadula sexnotata (Fallen) [=Macrosteles
quadrilineatus (Stal)] (Dobroscky 1931).
Foregut. Backus (1985) described the ciberial and esophageal regions of the
mouthparts of several leafhoppers. The foregut begins at the bases of the mandibular
and maxillary stylets with the precibarium. Fluid passes from the stylets to the pre
cibarium then into the cibarium (or sucking pump) and then to the esophagus. In both
D. maidis and G. nigrifrons the esophagus is a narrow tube that originates posteriorly
to the pharynx above the tentorial bar (Nault & Ammar, 1989); it continues posteri
orly until it enters the anterior midgut just below the filter chamber (E, Amg, Fc in
Figs. 1, 2, 3, and 4). Traversing parallel to the esophagus is a slender strand of cells
which is probably a suspensory ligament (Ammar 1985) (Sl in Figs. 1, 2, 3, and 4). This
strand originates near the esophageal valve (Ammar 1985) on the anterior midgut
and follows the esophagus into the head.


December, 1996
















Tsai & Perrier: Leafhopper Internal Morphology


Oe SI T
S S Mt -Oe
Pm
S Fc


Hg Am Am
Mt Mm Mm
Mt
Hg






Mt R
I



Fig. 1. G. nigrifrons. Dorsal view of digestive system of adult female. Sg, salivary
gland; Oe, esophagus; Sl, suspensory ligament; Fc, filter chamber; S, filter chamber
sheath, Mt, Malpighian tubules; Am, anterior midgut; Mm, mid-midgut; Pm, poste
rior midgut; Hg, hindgut; R, rectum. Vertical bar 1.0mm
Fig. 2. G. nigrifrons. Lateral right view of filter chamber. Oe, esophagus; Sl, sus
pensory ligament; Fc, filter chamber; S, filter chamber sheath; Mt, Malpighian tu
bules; Am; anterior midgut; Mm, mid midgut; Pm, posterior midgut; Hg, hindgut;
Vertical bar 1.0 mm.

Midgut and Filter Chamber Ingested fluid passes through the esophagus into the
anterior midgut. In both D. maidis and G. nigrifrons the anterior midgut is large and
sac-like (Am in Figs. 1 and 3), surrounded by a translucent muscular sheath composed
of circular fibers (Snodgrass 1935, Goodchild 1966). The anterior midgut extends from
the metathorax, nearly the entire length of the abdomen, and then constricts sharply
to become the mid-midgut (Am, Mm in Figs. 1 and 3). The mid-midgut then ascends,
returning to the anterior-most portion of the anterior midgut (Figs. 1 and 3: Mm); at
this point it swells slightly to form the posterior midgut and the beginning of the filter
chamber (Pm, Fc in Figs. 1 and 3).
In G. nigrifrons the posterior midgut forms a simple loop surrounding the top of
the anterior midgut (Pm, Fc in Figs. 1 and 2) where these two opposing ends of the
midgut appear to fuse (Bharadwaj et al. 1966). At the distal end of the loop, where it
exits the filter chamber, the posterior midgut constricts to form the hindgut (Hg in
Fig. 1). There appears to be a circular band of muscles at this junction, which is prob
ably the pyloric sphincter (Ammar 1985). This point marks the end of the filter cham-















Florida Entomologist 79(4)


Oe
S1S
s
Fc
Mt
Pm
Hg Am

Mm
Mt



1 /












Mt






Fig. 3. D. maidis. Dorsal view of digestive system of adult female. Sg, salivary
gland; Oe, esophagus; S1, suspensory ligament; Fc, filter chamber; S filter chamber
sheath, Mt, Malpighian tubules; Am, anterior midgut; Mm, mid-midgut; Pm, poste
rior midgut; Hg, hindgut; R, rectum. Vertical bar 1.0mm


December, 1996














Tsai & Perrier: Leafhopper Internal Morphology


SI 0
Oe

S


Mt
Fc



Hg Am


Mt


"1 ""Mm








Fig. 4. D. maidis. Lateral right view of filter chamber. Oe, esophagus; S1, suspen
sory ligament; Fc, filter chamber; S, filter chamber sheath; Mt, Malpighian tubules;
Am; anterior midgut; Mm, mid-midgut; Hg, hindgut; Vertical bar 1.0 mm.

ber (Fc in Fig. 1). A common sheath surrounds the filter chamber, enclosing the top of
the anterior midgut, the posterior midgut and the origins and proximal ends of the
Malpighian tubules (S, Am, Pm, Mt in Figs. 1 and 2). The gross morphology and
sheath formation of the filter chamber are similar to those of M. quadrilineatus (Do
broscky 1931), Eugnathodus indica Pruthi and Nephotettix apicalis Fabr. (Saxena
1955), Euscelidius variegatus (Khm.) and Euscelisplebejus (Fall) (Munk 1967) and A.
constricta (Bharadwaj et al. 1966). However, mesophyll feeding leafhoppers, such as
E. fabae, do not have a filter chamber (Berlin & Hibbs 1963).
The filter chamber of D. maidis is more complex than that of G. nigrifrons. The pos
terior midgut forms a deeper loop which covers the entire top of the anterior midgut
(Fc, Pm, Am in Figs. 3 and 4). The sheath covering this area appears to be formed in
sections, permitting fat bodies to attach themselves to the folds in the posterior mid
gut and to the anterior midgut around the periphery of the filter chamber.















Florida Entomologist 79(4)


Al PI

III I m
P1 IV


Sd --

Sa VI

Ag 3-Ag

a b c
Fig. 5. G. nigrifrons. Detail of salivary glands. a, anterior; b, material; c, posterior;
Pg, principal gland; Ag, accessory gland; Al, anterior lobe; Pl, posterior lobe; II-VI,
acini in principal gland; Sa, spherical appendage; Psd, principal salivary duct; Sd, sal
ivary duct. Vertical bar 0.25 mm.

Malpighian tubules. In both D. maidis and G. nigrifrons the Malpighian tubules
arise within the filter chamber from the posterior end of the posterior midgut (Pm, Mt
in Figs. 1 and 3). What appear to be three tubules loop back through the filter chamber
along the posterior midgut to emerge near the beginning of the chamber, or the ante
rior end of the posterior midgut (Pm, Mt in Figs. 1 and 3).
There are two pairs of Malpighian tubules. The central tubule is comprised of one
pair which is fused for the length of the filter chamber. Once this tubule emerges from
the filter chamber, it divides into two ureters. (Mt in Figs. 1, 2, 3, and 4). One ureter
extends behind the hindgut along with one tubule from the other pair (Mt, Hg in Figs.
1, 2, 3, and 4); the other ureter and tubule extend in front of the hindgut. Four Mal
pighian tubules were also found in M. quadrilineatus (Dobroscky 1931) and E. indica
and N apicalis (Saxena 1955) as well as E. fabae (Berlin & Hibbs 1963).

Al PI

III III
IV II V
Pe IV

Sdi VI
SaS
I I Sa Sd

Ag Ag
a b c

Fig. 6. D. maidis. Detail of salivary glands. a, anterior; b, lateral; c, posterior; Pg,
principal gland; Ag, accessory gland; Al, anterior lobe; Pl, posterior lobe; I-VI, acini in
principal gland; Sa, spherical appendage; Psd, principal salivary duct; Asd, accessory
salivary duct; Sd, salivary duct. Vertical bar 0.25mm.


December, 1996

















Tsai & Perrier: Leafhopper Internal Morphology


In G. nigrifrons, the three tubules run parallel to each other along the top of the
posterior midgut (Mt, Pm in Figs. 1 and 2); the central tubule is the fused pair. In D.
maidis, the central tubule (the pair) and one tubule from the other pair run along the
interior of the deep loop of the posterior midgut (Mt, Pm in Figs. 3 and 4); the other
tubule runs along the exterior of the loop (Mt in Figs. 3 and 4).
In both species, the Malpighian tubules appear translucent and lobulate for the
proximal third of their length after which they swell to become opaque and tubular
(Mt in Figs. 1 and 3). The four tubules extend toward the anus where they constrict
to become lobulate again. At this point the four tubules fuse and become loosely at
tached to the rectum by means of fibrous ligaments. (Mt in Figs. 1 and 3).
Hindgut. In both D. maidis and G. nigrifrons, the hindgut arises from the posterior
midgut at the boundary of the filter chamber. (Hg, Pm, Fc in Figs. 1 and 3). It extends
downward toward the anus where the hindgut swells to become the rectum (Hg, R in
Figs. 1 and 3). The hindgut passes in between the Malpighian tubules (Hg, Mt in Figs.
1 and 3).

Reproductive System

Female. The reproductive systems of D. maidis and G. nigrifrons are similar to
each other in most respects. The ovaries of both species contain six ovarioles (0, 01 in
Figs. 7 and 8). Each ovariole consists of a terminal filament, a germarium, developing
oocytes and eggs within follicles, and a pedicle (Tf, G, F, and P in Figs. 8b and c). The
ovarioles of both D. maidis and G. nigrifrons contain six follicles, the smallest of these
is closest to the germarium, the largest opens into the pedicle. The major difference
between the reproductive systems of the two species was observed within the ovariole.
In mature G. nigrifrons, each ovariole usually contains only one egg within the last
follicle (F in Fig. 9b). The follicle before the last is usually small, about one quarter the
size of the egg. The ovarioles of D. maidis often contain two eggs, one partially in the
last follicle and partially in the pedicle, the other in the previous follicle. When there
is only one egg, the follicle before the last is large, at least one half the size of the egg
(F, P in Fig. 9c). This could be one of the reasons that D. maidis is more prolific than
G. nigrifrons (Tsai 1988, unpublished).
Each ovariole ends anteriorly with a terminal filament which unites with those of
the other ovarioles to form a suspensory ligament (S1 in Figs. 7 and 8). These in turn
appear to attach with the ligaments of the other ovary to form a median ligament
which attaches dorsally to the body wall (Snodgrass 1935) at the roof of the second
thoracic segment. Posteriorly, the pedicle of each ovariole opens into the calyx of the
ovary (P, C in Figs. 7 and 8). These in turn open into the lateral oviducts, which join
to form the common oviduct (Lo, Co in Figs. 7 and 8). The common oviduct bends very
sharply toward the vagina (Co, V in Figs. 7 and 8). At the point where it opens into the
vagina, the common oviduct is joined by the globular to teardrop-shaped spermath
eca (Co, S, V in Figs. 7 and 8). Two types of glands are also present: a colleterial gland
and accessory glands (Cg, Ag in Figs. 7, 8 and 8a). These glands, along with the vagina
are attached to the opening of the ovipositor (OP in Figs. 7 and 8). The large tubular
colleterial gland, which often attaches itself to the neck and body of spermatheca, var
ies in length and can extend into the thorax (Cg, S in Figs. 7 and 8). The small, trans
lucent, tubular accessory glands appear to originate from within the vaginal wall as
a single gland which branches into two ducts. These ducts seem to extend through the
vaginal wall (V, Ag in Figs. 7, 8 and 9a). A similar female reproductive system was de
scribed for A. constricta (Gil-Fernandez & Black 1965) and M. fascifron (Becker 1979).
However, an average of ten ovarioles on each side of the ovary was observed for N.
cincticeps (Nasu 1965).












Florida Entomologist 79(4)


01












cLo
Co
Ag
Cg
V

Op .

I




Fig. 7. G. nigrifrons. Female reproductive system. Lateral view. 0, ovary; 01 ovar
iole; Sl, suspensory ligament; Ml, median ligament; P, pedicle; C, calyx; Lo, lateral ovi
duct; Co, common oviduct; S, spermatheca; Cg, colleterial gland; Ag accessory gland;
V, vagina; Op, ovipositor. Vertical bar=1.0 mm.


December, 1996













Tsai & Perrier: Leafhopper Internal Morphology


Lo


CO


'
Ag
C ~g VA


Op







Fig. 8. D. maidis. Female reproductive system. Lateral view. 0, ovary; 01, ovariole;
Sl, suspensory ligament; Ml, median ligament; P, pedicle; C, calyx; Lo, lateral oviduct;
Co, common oviduct; S, spermatheca; Cg, colleterial gland; Ag accessory gland; V, va-
gina; Op, ovipositor. Vertical bar=l.0 mm.














Florida Entomologist 79(4)


Ag








a P




b c
Fig. 9a. D. maidis and G. nigrifrons female. Ventral view. V, vagina; Ag, accessory
gland. Vertical bar 1.0 mm.
Fig. 9b. G. nigrifrons detail of ovariole.
Fig. 9c. D. maidis detail of ovariole. Tf, terminal filament; G, germarium; F, folli
cles; P, pedicle. Vertical bar 0.5 mm.

Male. Both D. maidis and G. nigrifrons have two lateral testes situated ventrally
at the junction of the abdomen and the thorax (T in Figs. 10 and 1 la). The testes,
which contain six follicles each, are often surrounded by fat bodies. The ovoid follicles
join at the base of the testes to open into the very narrow vas deferens (T, Vd in Figs.


December, 1996












Tsai & Perrier: Leafhopper Internal Morphology


T

Vd

Cs

Sv


Le
Ag /
Ce /





\9/
Fig. 10. G. nigrifrons. Male reproductive system. Ventral view. T, testes; Vd, vas
deferens; Sv, seminal vesicle; Cs, common sheath; Le, lateral ejaculatory duct; Ce,
common ejaculatory duct; Ag, accessory gland. Vertical bar=1.0 mm.










Florida Entomologist 79(4)


Ag
Vd






.Sv





Le




S.- Ce

Fig. 11. D. maidis. Male reproductive system. Lateral view. Vd, vas deferens; Sv,
seminal vesicle; Le, lateral ejaculatory duct; Ce, common ejaculatory duct; Ag, access
sory gland. Vertical bar=1.0 mm.


December, 1996




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