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Evaluation of Predatory Mites and Acramite for Control of Twospotted Spider Mites in Strawberries in North Central Florida
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 Material Information
Title: Evaluation of Predatory Mites and Acramite for Control of Twospotted Spider Mites in Strawberries in North Central Florida
Series Title: J. Econ. Entomol. 99(4): 1291-1298 (2006)
Physical Description: Journal Article
Language: English
Creator: Rhodes, Elena M.
Liburd, Oscar E.
Publisher: Entomological Society of America
Publication Date: 2006
 Subjects
Subjects / Keywords: Acramite
Neoseiulus californicus
Phytoseiulus persimilis
twospotted spider mite
strawberry
 Notes
Abstract: Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (<10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.
Funding: Support for the development of the technical infrastructure and partner training provided by the United States Department of Education TICFIA program.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Dina Benson.
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System ID: IR00000080:00001

Full Text
HORTICULTUBAL ENTOMOLOCJY
Evaluation of Predatory Mites and Acramite for Control of Twospotted
Spider Mites in Strawberries in North Central Florida

ELENA M. RHODES and ÓSCAR E. LIBURD
Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611
]. Econ. Entomol. 99(4): 1291-1298 (2006)
ABSTRACT Greenhouse and field experiments were conducted from 2003 to 2005 to determine the
effectiveness of two predatory mite species, Phjtoseiuhjs persimilis Athias-Henriot and Neoseiulus
californicwi (McGregor), and a reduced-risk miticide, Acraniite 30 WP (bifenazate), for control of
twospotted spider niite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In
greenhouse tests, three treatments consisting of releases of P. persimilis, N. calijomicus, and an
untreated control were evaluated. Both species of predatory mites significantly reduced twospotted
spider mite numbers below those found in the control during the first 3 wk of evaluation. However,
during week 4, twospotted spider mite nunibers on the plants treated with P. persimilis increased and
did not differ significantly from the control. Field studies used releases of P. persimilis and N.
californiciis, applications of Acramite, and untreated control plots. Both ?v. califoniicus and P. persimilis
significantly reduced populations of twospotted spider mite below numbers recorded in the control
plots. During the 2003-2004 field season P. persimilis took longer than N. calijomicus to bring the
twospotted spider mite population under contxol (<10 mites per leaflet). Acramite was effectíve in
reducing twospotted spider mite populations below 10 mites per leailet during the 2003-2004 field
season but not during the 2004 -2005 field season, possibly because of a late application. These findings
indícate that JV. californicus releases and properly timed Acraniite applications are promising options
for twospotted spider mite control in strawberries for growers in north Florida and other áreas of the
southeast.

KEY WORDS Acramite, Neoseiulus calijomicus, Phytoseiulus persimilis, twospotted spider mite,
strawberry
The twospotted spider mite, Tetranychus urticae Koch,
is the key arthropod pest affecting stiawberries (Fra-
garia X anatuissa Duchesne) in Florida (Mossler and
Nesheim 2003). Their feeding causes injury to chlo-
rophyll containing mesophyll cells within the leaf tis-
sue, which results in a decrease of photosynthetic
capacitíes of infested leaves (Sanees et al. 1982). Early
season infestations of twospotted spider mites cause
reductions in photosynthesis and transpiration at a
niuch lower population level than the population level
that causes the same level of injury later in the season
(Sanees et al. 1981).
Development from egg to mature adult takes '=19 d
(Mitchell 1973), although this time can be as short as
5 d (Ho and Lo 1979). Optimal conditions for devel-
opment are high temperatures (up to 38°C) and low
humidity (White and Liburd 2005). Their high fecun-
dity and short life cycle allow twospotted spider mites
to quickly beconie resistant to miticides used to con-
tiol them. The use of reduced-risk miticides and pe-
riodic releases of predatory mites may give growers
more options for management of twospotted spider
mites.
Acramite 50 WP (bifenazate) (Cronipton, Morgan-
town, WV) is a reduced-risk miticide that has shown
promising results in stiawberries (Liburd et al. 2003).
This miticide has alow toxicity toward predatory mites
(White 2004). Acramite can only be applied twice in
a season at 0.85-1.125 kg of product per hectare with
applications at least 21 d apart (Price 2002, Mossler
and Nesheim 2003). In laboratory studies using leaf
disks, White (2004) recorded ahigher rate of twospot-
ted spider mite mortality using Acramite 50 WP com-
pared with the conventional miticide Vendex (fen-
butatin oxide) (DuPont, Wilmington, DE).
Phytoseiulus persimilis Athias-Henriot and Neoseiu-
lus calijomicus (McGregor) are predatory mites be-
longing to ihe family Phytoseiidae. They have been
shown to effectively control twospotted spider mites
on strawberry and other crops in various parts of the
world (Port and Scopes 1981, Cross 1984, Charles et al.
1985, Charles 1988, Waite 1988, Easterbrook 1992, De-
cou 1994, Cross et al. 1996, Garcia-Mari and González-
Zamora 1999, Easterbrook et al. 2001, Barber et al.
2003, Liburd et al. 2003). Phytoseiulus persimilis and >V.
califomicus are also effective in controlling twospot-
ted spider niites on strawberries in California (Oat-
0022-0493/06,.'129i-i298$04.00/0 © 2006 Entomoiogical Society of America


1292
Journal of Economic Entomology
Vol. 99, no. 4
man et al. 1967, 1968, 1976, 1977a,b; Trumble and
Morse 1993). Phytoseiulus persimilis is a type I spe-
cialist that feeds exclusively on Tetranychus mites
(McMurtry and Croft 1997). In contiast, N. califomi-
cus has tiaits of both a type II specialist and a type ITT
generalist (Croft et al. 1998). N. califomicus prefer
spider mites as food but can subsist on other sources
of food such as thrips and poUen when mite popula-
tions are low, and they also prey upon other predatory
mite species (Gerson et al. 2003).
In Florida, seasonal releases of P persimilis have
been fairly successful in contioUing twospotted spider
mite populations in the southern regions of the state
(Decou 1994). However, releases of P persimilis have
not been effective in northern Florida, possibly be-
cause it may not be able to survive the winter typical
of this área (White 2004). Preliminary studies by
Liburd et al. (2003) indícate that N. califomicus may
be able to effectively control twospotted spider mite
in north Florida strawberries where P persimilis is
ineffective.
The objective of these experiments was to compare
the efficacy of both species of predatory mites for
contiol of twospotted spider mites under contioUed
greenhouse conditions and under field conditions in
north Florida. Under controUed greenhouse condi-
tions, P persimilis would be expected to perform as
well as or better than N. califomicus because temper-
ature effects are not a factor.
In the field, our hypothesis was that N. califomicus
would provide better contiol of twospotted spider
mites compared with P persimilis. Furthermore, both
N. califomicus and Acramite would significantly re-
duce populations of twospotted spider mites in stiaw-
berries to below levéis found in untieated (contiol)
plots.

Materials and Methods
Colony. A twospotted spider mite colony reared on
stiawberries was maintained in the laboratory to en-
sure that only twospotted spider mites predisposed to
stiawberries were used in the experiments. The col-
ony consisted of mite-infested stiawberry plants that
were kept under a photoperiod of 14:10 (L:D) regime
at a temperature of '=27°C with 65% RH. Plants were
watered twice weekly.
Predatory mites used in all experiments were ob-
tained from Koppert Biological Systems (Romulus,
MI). Predatory mites were used within 48 h of their
arrival dates.
Greenhouse Experiment. Fifteen mite-free 'Festi-
val' strawberry plants with a total of four tiifoliates
were placed into previously constiucted mite-free
cages (Fig. 1). Each plant was placed into an individual
cage (60 by 30 by 20 cm). Cages were constructed of
nylon fabric. Velero was placed on three sides of the
cage to gain easy access to the plants. Each cage was
attached to a pot containing a stiawberry plant by
using a pulí cord sown into the bottom of the cage.
Cages were used to keep both twospotted spider mites
and predatory mites from dispersing between plants.
Fig. 1. Mite-free cages (60 by 30 by 20 cm) containing
strawberry plants.
Ten twospotted spider mites were released onto each
plant and allowed to multiply for 1 to 2 wk (this varied
depending on when the predatory mite shipment ar-
rived). Before the reléase of predatory mites, a leaflet
was coUected from each plant. The number of
twospotted spider mite motiles and eggs on each leaf-
let was counted, and the mean number per leaflet was
calculated. The average reléase rate was approxi-
mately a 10:1 ratio (10 twospotted spider mite to one
predatory mite). Also, a representative sample (one
bottle from each species of predatory mite) was ob-
served for at least 15 min to ensure that the shipped
predatory mites were active and in good condition
before use.
Experimental design was a completely randomized
block with three tieatments. Each tieatment was rep-
licated five times. Treatments included 1) 10 P per-
■similis adults released per infested plant («^lOO
twospotted spider mites), 2) 10 N. califomicus adults
released per infested plant («^lOO twospotted spider
mites), and 3) untieated (control) plants («^lOO
twospotted spider mites) without predatory mites.
Sampling. Each week the population of predators
and twospotted spider mites was sampled by taking
one leaflet from each plant (five leaflets from each
individual treatment) and counting the numbers of
twospotted spider mites as well as predatory mites
(motiles and eggs). The term motiles refers to all life
stages except eggs. Samples were recorded for 4 wk.
Three triáis of this experiment were run: the first trial
was conducted in February / March 2004, the second in
December 2004/January 2005, and the third in March/
Aprfl 2005.
Data Anaiysis. Twospotted spider mite motile and
egg data were log transformed. Mean twospotted spi-
der mites per leaflet was compared each week across
tieatments by using an anaiysis of variance (ANOVA),
and means were separated using a least significant
difference (LSD) test (SAS Institute 2002).


August 2006
Rhodes and Liburd: Control of Twospotted Spider Mites
1293
Field Experiment. The field experiment was con-
ducted at the University of Florida, Plant Science
Research Unit, Cifra, FL. Festival strawberry plants
were planted in mid-October. They were grown as an
annual crop on raised beds covered by black plástic
mulch. A combination of overhead and drip irrigation
was used for the first 3 wk to help establish the tians-
plants. After this establishment period, only drip irri-
gation was used. Stiawberries were planted in plots 7.3
by 6.1 m consisting of six rows 0.5 m wide with 0.5-m
row spacing. There were 24 plots arranged in a 4 by 6
grid and spaced 7.3 m apart. The experiment was a
completely randomized block design with six replí-
cales. Four treatments were evaluated and included 1)
two releases of P persimilis (P), 2) two releases of N.
califomicus (N), 3) two applications ofthe reduced-
risk miticide Acramite 50 WP at the rate of 1.125 kg of
product per hectare (A), and 4) an untieated contiol
(C). In the 2003-2004 field season, all tieatments were
applied during the weeks of 11 December and 11
February. In the 2004 -2005 field season, all tieatments
were applied on 9 December and again on 10 March.
Predatory mites were applied at a rate of one bottle
(2000 mites) per plot by hand by gently rotating the
bottle over each plant. Acramite was sprayed using a
11-liter (3-gal) backpack sprayer.
Sampling. Sampling was initiated once the plants
had established ('=3 wk after planting). Each week, six
leaves per plot (36 leaves per treatment) were col-
lected randomly from the middle and lower stiata of
each plant and brought back to the laboratory where
the number of twospotted spider mite motiles and
eggs and predatory mite motiles and eggs on each leaf
were counted under a dissecting microscope. Only P
persimilis and N. califomicus mites were counted.
Data Anaiysis. The twospotted spider mite motile
and egg data were separated into five periods based on
tieatment application dates and time during the sea-
son. This was also important to examine trends
throughout the 4-mo field season. These periods were
1) pretieatment (3 wk before any tieatment), 2) ear-
ly-season (posttieatment to week 7), 3) mid-season
(week 8 to when the second application was applied
in 2003-2004 at week 12), 4) early-late season (week
13 to when the second tieatment was applied in the
2004-2005 season at week 16), and 5) late season
(weeks 17-19). The late season was split into two
periods because of the difference in timing of the
second application between seasons. For example,
during the 2003-2004 season, the second application
occurred at the beginning of the late season, whereas
in the 2004 -2005 field season, the second application
occurred in the middle of the late season. In each
period, data were log tiansformed and then tieatments
were compared using an ANOVA, and means were
separated using an LSD test (SAS Institute 2002).
Yield. Yield data were coUected beginning in early
January in both seasons. Strawberries were harvested
weekly by hand. Marketable stiawberries from the
four inner rows were weighed on abench scale (Met-
tler Toledo, Columbus, OH). Damaged, rotten, and
severely deformed stiawberries were discarded. The
a.
25 -1
20 ■
a 15 ■
E 10 ■
Í2 5 ■ 0 ■
0 12 3 4
Week after predatory mite reléase
b.
50 1
1 40 ■
0) a. 30 ■
(fí lo ■ 0 •
Week after predatory mite reléase
Fig. 2. Weekly mean ± SEM twospotted spider mite
(TSSM) (a) motiles and (b) eggs per leaflet in each treat-
ment in the greenhouse experiment. Week O is the initial
sample taken before predatory mites were released. Means
on the same date followed by the same letter are not signif-
icantly different by LSD (P = 0.05) (C, control; P, P. persi-
milis; and N, N. califomicus).


two outer rows served as border rows and the stiaw-
berries from these rows also were discarded.
Data Anaiysis. The mean yield per treatment for
the whole season was compared across tieatments
using an ANOVA (SAS Institute 2002). A LSD test was
used to show tieatment differences for the yield data.
This was done for both field seasons.


Results

Greenhouse Experiment. There were no significant
differences in twospotted spider mite motile and egg
populations among tieatments when the initial sample
was taken (week 0) (motiles: F = 1.1; df = 2, 24; P =
0.3638; eggs: F = 0.94; df = 2, 24; P = 0.4046) and 1 wk
after predatory mite reléase (motiles: F = 0.08; df = 2,
24; P = 0.9257; eggs: F = 0.45; df = 2, 24; P = 0.6441)
(Fig. 2). Two weeks after the reléase of predatory
mites, P persimilis significantly reduced twospotted
spider mite motile and egg numbers below numbers in
die contiol (motiles: F = 3.4; df = 2, 24; P = 0.0513;
eggs: F = A.A; df = 2, 24; P = 0.0230). However,
twospotted spider mite numbers on plants where N.
califomicus was released were intermedíate, averaging


1294
Journal of Economic Entomology
Vol. 99, no. 4
1.3 ± 1.3 motiles and 9.7 ± 8.4 eggs per leaflet (Fig. 2).
Both species of predatory mites significantly reduced
numbers of twospotted spider mite motiles and eggs
below the contiol by week 3 (motiles: F = 6.2; df = 2,
24; P = 0.0068; eggs: F = 6.0; df = 2, 24; P = 0.0075).
Twospotted spider mite motile and egg numbers on
plants where P persimilis were released began to in-
crease at week 4 and were not significantly different
from the contiol. At this time, there were significantly
fewer motiles per leaflet in the N. califomicus tieat-
ment compared with the other two tieatments (mo-
tiles: F = 4.3; df = 2, 24; P = 0.0256). However, tire
difference in egg numbers was not significant (eggs:
F= 1.9; df = 2, 24;P = 0.1717).
One week after predatory mite reléase, there were
an average of 0.1 ± 0.1 P persimilis motiles per leaflet
in the P persimilis tieatment. This increased to 0.5 ±
0.2 motiles per leaflet at week 2 and 0.7 ± 0.6 motiles
per leaflet at week 3. The population then decreased
to 0.3 ± 0.2 motiles per leaflet at week 4. Only one P
persimilis egg was recorded in the study at week 4 in
the third tiial of the experiment.
In contiast, N. califomicus numbers in the N. cali-
fomicus treatment were similar throughout the study.
There were an average of 0.7 ± 0.5, 0.7 ± 0.4, 0.6 ± 0.3,
and 0.6 ± 0.3 motiles per leaflet at weeks 1, 2, 3, and
4, respectively. In total, seven eggs were laid during
the experiment: four at week 1 in the first tiial, one at
week 2 in the third tiial, and two at week 3 in the
second tiial.
Field Experiment. 2003-2004 Field Season. There
were no significant differences in motile and egg num-
bers among tieatments in the pretieatment period
(motiles: F = 0.8; df = 3, 15; P = 0.5041; eggs: F = 0.7;
df = 3,15; P = 0.5805) or in the early-season (motiles:
F = 0.7; df = 3, 15; P = 0.5511; eggs: F = 1.4; df = 3,
15; P = 0.2755) (Fig. 3). The N. califomicus and Ac-
ramite treatments had significantly fewer motiles and
eggs per leaflet than the contiol plots during the mid-
season (motiles: F = 3.9; df = 3, 15; P = 0.0297; eggs:
F = 5.0; df = 3,15; P = 0.0137) and during the early-late
season (motiles: F = 5.1; df = 3, 15; P = 0.0121; eggs:
F = 4.0; df = 3, 15; P = 0.0280) (Fig. 3). During these
two periods, twospotted spider mite numbers in the P
persimilis treatment were fairly high but were not
significantly different from twospotted spider mite
numbers in the N. califomicus tieatment. Also, num-
bers of twospotted spider mite in the P persimilis
tieatment were not significantly different from those
in the contiol with the exception of the early-late
season in terms of the numbers of motiles (Fig. 3).
There were no significant differences in twospotted
spider mite motile and egg numbers among tieatments
in the late season (motiles: F = 1.2; df = 3, 15; P =
0.3461; eggs: F = 0.68; df = 3, 15; P = 0.5777).
Predatory mites were observed from 17 December
until 17 March (mid- and early-late seasons). In the P
persimilis tieatment, the P persimilis population be-
gan increasing on 7 January reaching a peak of 1.4 ±
0.4 motiles and 1.6 ± 0.4 eggs per leaflet on 20 January.
The population remained high for several weeks then
declined sharply on 20 February and remained low.
^i^
pretrt
early
mid

Period
early-late
160

140

120

100

80

60

40

20

O
í
MM
s
be
fe
K
pretrt early mid early-late late
Period

Fig. 3. Mean ± SEM twospotted spider mite (TSSM) (a)
motiles and (b) eggs per leaflet for flve periods of the 2003-
2004 fleld season. Means on the same date followed by the
same letter are not signiflcantly different by LSD (P = 0.05)
(C, control; P, P. persimilis; N, N. califomicus; A, Acramite).
No P persimilis were recorded after 17 March. In the
N. califomicus tieatment, the N. califomicus popula-
tion began to increase at 17 December, reaching a
peak of 1.0 ± 0.3 motiles and 0.6 ± 0.1 eggs per leaflet
on 2 February. The population declined sharply at 25
February. After this date, no N. califomicus were re-
corded with the exception of a small number noted on
30 March (no twospotted spider mites were recorded
after 25 February in this tieatment either). Very small
numbers of motiles of both species were recorded
from the Acramite tieatment the week after each
reléase. However, no eggs were ever recorded. Small
numbers of both species dispersed into the contiol
plots and were recorded from 2 February until 9
March. The combined population never exceeded
0.4 ± 0.3 motiles or 0.2 ± 0.2 eggs per leaflet.
2004 -2005 Field Season. During the 2004 -2005 field
season, the twospotted spider mite population peaked
much later in the season. There were no significant
differences in twospotted spider mite motile and egg
numbers in the pretieatment period (motiles: F = 0;
df = 3, 15; P = 1; eggs: F = 0; df = 3, 15; P = 1) or in
the early-season (motiles: F = 0.47; df = 3, 15; P =
0.7073; eggs: F = 0.57; df = 3, 15; P = 0.6432) (Fig. 4).


August 2006
Rhodes and Liburd: Control of Twospotted Spider Mites
1295
a.
■ c
DP
DN
DA .í r 1 T
a b
ll
,i J ,1% ^c
pretrt early mid
Period

b.
■ c ■ P DN DA 1 . > a be b
pretrt early mid early-late late
Period

Fig. 4. Mean ± SEM twospotted spider mite (TSSM) (a)
motiles and (b) eggs per leaflet for flve periods ofthe 2004-
2005 fleld season. Means on the same date followed by the
same letter are not signiflcantly different by LSD (P = 0.05)
(C, control; P, P. persimilis; N, N. califomicus; and A, Ac-
ramite) .

There were also no significant differences in twospot-
ted spider mite motile or egg numbers in the mid-
season (motiles: F = 1.9; df = 3, 15; P = 0.1699; eggs:
F = 2.4; df = 3, 15; P = 0.1129). However, twospotted
spider mite egg numbers showed a trend of being
higher in the Acramite tieatment compared with the
N. califomicus tieatment during the mid-season (Fig.
4). The control tieatment had significantly higher
numbers of twospotted spider mite motiles and eggs
than the N. califomicus and P persimilis tieatments in
the early-late season (motiles: F = 11.1; df = 3, 15; P
= 0.0004; eggs: F = 13.0; df = 3, 15; P = 0.0002) and
die late season (motiles: F = 14.6; df = 3,15; P = 0.0001;
eggs: F = 14.6; df = 3,15; P = 0.0001) (Fig. 4). During
the early-late season, numbers of twospotted spider
mite motiles in the Acramite treatment did not differ
significantly from those found in the control. How-
ever, there were significantly less twospotted spider
mite eggs in the Acramite tieatment during this period
than in the contiol. The Acramite tieatment had sig-
nificantly higher numbers of twospotted spider mite
motiles and eggs than both predatory mite tieatments
in the early late season. In the late season, the Ac-
ramite tieatment had significantly more twospotted
Table 1. Mean total marketable strawberry yield from each
treatment for the 2003-2004 and 2004-2005 field season

Treatment Mean ± SEM total yield (kg) of strawberries
2003-2004 2004-2005
Acramite N. califomicus F. persimilis Control 93.9 ± 4.9ab 98.3 ± 3.8a 83.1 ± 4.8b 83.1 ± 7.6b 39.2 ± 1.8 35.1 ± 1.4 37.2 ± 0.9 38.9 ± 1.1
Means witliin a season followed by tlie same letter are not signif-
icantly different (LSD test; P = 0.05).
spider mite motiles than both predatory mite tieat-
ments and significantly more twospotted spider mite
eggs than the N. califomicus tieatment (Fig. 4).
Predatory mites were observed from 12 January
until 30 March (mid, early-late, and late seasons).
Observations were sporadic until 23 February. In the
P per.sim,ilis tieatment, P per.sim,ilis motiles and eggs
were recorded continuously from 9 March until 30
March. The population never rose above 0.1 ± 0.1
motiles or 0.1 ± 0.03 eggs per leaflet. In the N. cali-
fomicus tieatment, N. califomicus motiles and eggs
were recorded continuously from 23 February until 25
March. The population never rose above 0.2 ± 0.1
motiles or 0.3 ± 0.1 eggs per leaflet. In total, two P
persimilis motiles and four P persimilis eggs were
recorded in the Acramite treatment on 25 March, and
one egg was recorded on 16 March. Both species
dispersed into the control plots and were recorded
from 23 February until 30 March. The combined pop-
ulation reached a peak of 0.4 ± 0.1 motiles and 0.4 ±
0.1 eggs per leaflet on 25 March and then declined
slightly by 30 March.
Yield. In the 2003-2004 season, the mean total mar-
ketable yield from the P persimilis treatment was not
significantly different from the control (Table 1). The
total marketable yield for the N. califomicus tieatment
averaged significantly higher than the P persimilis and
contiol tieatments (F = 3.36; df = 3, 15; P = 0.0376).
The total marketable yield for the Acramite tieatment
was not significantly different from the other three
tieatments.
In contrast, in the 2004 -2005 season, there were no
significant differences in mean total marketable yield
between the four tieatments (F = 2.6; df = 3, 15; P =
0.0907) (Table 1). Mean total marketable yield per
tieatment was much lower than the previous season.
Marketable yields averaged between 35 and 40 kg per
tieatment compared with 85-90 kg per tieatment in
die 2003-2004 field season.


Discussion

Greenhouse Experiment. Our results indícate that
both species of predatory mites significantly reduced
twospotted spider mite numbers below those found in
the contiol. N. califomicus suppressed twospotted spi-
der mite populations for a longer time period and its
population remained relatively constant throughout
the experiment. However, these predators initially


1296
JOLTíNAL OF Economic Entomology
Vol. 99, no. 4
took longer (1 wk) than P persimilis to reduce
twospotted spider mite numbers below the control.
This was not sm"prising because P. persimilis is known
to quickly knock down twospotted spider mite pop-
ulations under controlled conditions (Gilstrap and
Friese 1985). In our studies, P persimilis seems to be
unable to sustain suppression of twospotted spider
mite beyond 3 wk in the greenhouse. The twospotted
spider mite population increased at week 4, whereas
the P. persimiils population declined. The reason for
this may be related to its biology. As a type I specialist,
P persimilis cannot survive in áreas where its food
supplies are low. Therefore, once the twospotted spi-
der mite population has been greatly reduced, P per-
similis must disperse to a new location to find food
(McMurtry and Croft 1997). Both species of predatory
mites laid very few eggs. We do not know why this
occurred, but we speculate that there was not enough
twospotted spider mite prey for either species to pro-
duce large numbers of eggs.
Field Experiment. In both field seasons, there were
fewer twospotted spider mites in the N. califomicus
treated plots compared with ihe P. persámíis-treated
plots, although die difference in íhe 2004 -2005 season
was not significant. This su,ggests that N. califomicus
may be better at reducing or regulating field popula-
tions of twospotted spider mite than P. persimilis In
this study, we do not think that environmental con-
ditions contiibuted to the better performance of N'.
caüjomictis because similar results were obtained in
the greenhouse under controlled conditions.
Acramite was highly effective in die 2003-2004 sea-
son, but did not adequately control twospotted spider
mite populations in the 2004-2005 season. This was
primarily a result of timing. In the 2003-2004 season,
the first spray knocked down the twospotted spider
mite population and the second spray in early Feb-
ruary kept the numbers low. During die 2004-2005
season, in contrast, there were no detectable twospot-
ted spider mite populations when Acramite was first
sprayed. By the time twospotted spider mite popula-
tions began to increase, there was little residual ac-
tivity left in the Acramite plots. We delayed die sec-
ond application of all treatments until March during
the 2004 -2005 field season so that twospotted spider
mite populations could have a chance to increase.
Because the Acramite plots were essentially controls
(because of delayed application), íhe twospotted spi-
der mite population in these plots exploded and was so
high that the second application of Acramite could not
significantly reduce twospotted spider mite levéis.
This illustrates the importance of properly timing Ac-
ramite applications for growers. Using Acramite in
combination with other management tactics (preda-
tory mites) to control twospotted spider mites might
avoid such problems, although further research would
be needed to demónstrate this possibility.
There were several differences in the twospotted
spider mite populations between the two field seasons.
In the 2003-2004 season, twospotted spider mites were
present in die plots from the start of die experiment,
diey began to increase when die temperature began
to increase, and then declined by the last few weeks
of the season. In contrast, no detectable numbers of
twospotted spider mites were found in the 2004-2005
season until mid-January, and the numbers of twospot-
ted spider mite did not increase greatly until late
February. Overall, both twospotted spider mite and
predatory mite numbers were much lower in the
2004-2005 season. White and Liburd (2005) found
diat twospotted spider mites prefer hot, dry condi-
tions, and die late summer and fall 2004 were incred-
ibly wet because of hurricanes Francis and Jeanne.
This may have knocked back the surrounding popu-
lation of twospotted spider mites, leaving smaller num-
bers to disperse into the strawberries when they were
planted.
Another difference in the twospotted spider mite
populations between seasons was that the presence of
the green form of twospotted spider mite was much
more prevalent than the red form in 2003-2004. This
tiend reversed itself in 2004 -2005. The red and green
forms were considered sepárate species until Hino-
moto et al. (2001) showed that reproductive incom-
patibility between the two forms is incomplete. Using
cytochrome oxidase subunitlsequences, Hinomoto et
al. (2001) demonstiated that the two forms belong to
the same species from a phylogenetic standpoint. We
do not know why die green form predominated in
2003-2004 and the red predominated in 2004-2005.
This would be an interesting topic to research further.
Predatory mite population trends also differed
greatly between seasons. In 2003-2004, both species
were abundant when twospotted spider mite popula-
tions were high, declining when prey populations di-
minished. In 2004-2005, predatory mites also were
present when twospotted spider mite populations
were high (compai-ed with the rest of the season).
However, overall predatory mite populations were
much lower than those in the previous season. This
was probably because of the overall much lower
twospotted spider mite population in the 2004-2005
season.
Yield. During the 2003-2004 field season, the 'N.
califomicus treatment had a significantly higher mean
total marketable yield than both the contiol and P
persimilis ti-eatments. However, during the 2004-2005
field season, there were no significant differences
among treatments. The difference in twospotted spi-
der mite population tiends between the two seasons
may partially explain why there were significant dif-
ferences between treatments in 2003-2004 but not in
2004-2005. Sanees et al. (1981) found that higher
numbers of twospotted spider mites are needed to
cause a similar level of damage when infestation oc-
curs later in the setison. That the twospotted spider
mite population in 2004 -2005 was so low and twospot-
ted spider mites occurred so late in die season sug-
gested that the numbers of twospotted spider mites
were not high enough to affect die quantity of stiaw-
berries produced during the 2004-2005 field season.
Other factors that may have contiibuted to the lack of
significant differences in the 2004-2005 field season
were a greater amount of fungal problems, including


August 2006
Rhodes and Liburd: Control of Twospotted Spider Mites
1297
Anthracnose fruit rot, Colhtotrichum acutatum Sim-
monds, and gray, mold Botrytis cinérea Pers; bird dam-
age; and weed infestation in 2004 -2005. These factors
also may have lead to the overall lower marketable
yields in 2004-2005 compared with 2003-2004.
Overall, releases of N. calijomicus seem to be a
viable tactic for north Florida strawberry growers.
Acramite is very effective if applications are timed and
applied properly. Application of Acramite followed by
the reléase of an effective predatory mite such as N'.
caüjomictis may be an effective management tactic for
stiawberry growers in north Florida. Further research
on combination tieatments is needed before definite
conclusions can be drawn.
Acknowledgments

We thank Scott Taylor and the staff at tlie Citra Plant
Science Research and Education Unit located in Citra, FL,
for assistance in managing our research plots. We also thank
Alejando Arevalo, Marínela Capana, and Raymond Littell for
help with the statistical anaiysis. Finally, we thank all the staff
and students of the University of Florida Small Fruit and
Vegetable Integrated Pest Management Laboratory in
Gainesville Florida, especially Crystal Kelts, for assistance in
the fleldwork. We thank Robert Meagher and Donald Dick-
son for editing the earlier drafts of this manuscript. Funding
for this project was provided by an EPA Región four Straw-
berry IPM Grant 736404813.
References Cited

Barber, A., C.A.M. Campbell, H. Crane, R. Lilley, and E.
Tregidga. 2003. Biocontrol of two-spotted spider mite
Tetranychus urticae on dwarf hops by the phytoseiid mites
Phyto.seiulus persimilis and Neoseiubis califomicus. Bio-
control Sci. Technol. 13: 275-284.
Charles, J. G. 1988. Using Phyto,seiulus persimilis to control
two-spotted mites in strawberry, pp. 202-206. in Proceed-
ings of the 41st New Zealand Weed and Pest Control
Conference.
Charles, J. G., E. Coilyer, and V. White. 1985. Integrated
control of Tetranychus urticae with Phytoseiulus persimilis
and Stethorus hifidus in commercial raspberry gardens. N
Z J. Exp. Agrie. 13: 385-393.
Croft, B. A., L. N. Monetti, and P. D. Pratt. 1998. Compar-
ative life histories and predation types: are Neoseiulus
californicus and N. fallacis (Acari: Phytoseiidae) similar
type 11 selective predators of spider mites. Environ. En-
tomol. 27: 531-538.
Cross, J. V. 1984. Biological control of two-spotted spider
mite {Tetranychus urticae) by Phijtoseiulus persimilis on
strawberries grown in 'walk-in' plástic tunnels, and a
simplifled method of spider mite population assessment.
Plant Pathol. 33: 417-423.
Cross, J. V., C.M. Burgess, and G.RHanks. 1996. Integrat-
ing insecticide use with biological control of two spotted
spider mite {Tetranychus urticae) by Phytoseiulus persi-
milis on strawberry in the UK. pp. 899 -906. Brighton Crop
Protection Conference - Pests and Diseases, 18-21 No-
vember 1996, Brighton, United Kingdom.
Decou, G. C. 1994. Biological control of the two-spotted
spider mite (Acariña: Tetranychidae) on commercial
strawberries in Florida with Phyto.seiulus persimilis (Aca-
riña: Phytoseiidae). Fia. Entomol. 77: 33-41.
Easterbrook, M. A. 1992. The possibilities for control of two-
spotted spider mite Tetranychus urticae on fleld-grown
strawberries in the UK by predatory mites. Biocontrol Sci.
Technol. 2: 235-245.
Easterbrook, M. A., J. D. Fitzgerald, and M. G. Solomon.
2001. Biological control of strawberry tarsonemid mite
Phytonemus pallidus and two-spotted spider mite Tetrany-
chus urticae on strawberry in the UK using species of
Neoseiulus (Amblyseius) (Acari: Phytoseiidae). Exp.
Appl. Acai-ol. 25: 25-36.
García-Mari, F., and J. E. González-Zamora. 1999. Biologi-
cal control oí Tetranychus urticae (Acari: Tetranychidae)
with naturaily occurring predators in strawberry piant-
ings in Valencia, Spain. Exp. Appl. Acarol. 23: 487-495.
Gerson, U., R. L. Smlley, and R. Ochoa. 2003. Mites (Acari)
for pest control. Blackwell Pubflshing. Ames, L4..
Gilstrap, F. E., and D. D. Friese. 1985. The predatory po-
tential of Phijtoseiulus persimilis, Amblyseius califomicus,
and Metaseiulus occidentalis (Acaiina: Phytoseiidae). Int.
J. Acaro!. 11: 163-168.
Hinomoto, N., M. Osakabe, T. Gotoh, and A. Takafuji. 2001.
Phylogenetic anaiysis of green and red forms ofthe two-
spotted spider mite, Tetranychus urticae Koch (Acari:
Tetranychidae), in Japan, based on mitochondria! cyto-
chrome oxidase subunit I sequences. Appl. Entomol.
Zool. 36: 459-464.
Ho, C. C, and K. C. Lo. 1979. Influence of temperature on
Ufe history and population parameters of Tetranychus
urticae. Agrie. Res. China 28: 261-271.
Liburd, O. F,., G. G. Seferina, and D. A. Dinkins. 2003.
Suppression of twospotted spider mites. University of
Florida. Institute of Food and Agricultural Sciences Ext.
Newsl. Berry/Vegetable Times 3: 3-4.
McMurtry, J. A., and B. A. Croft. 1997. Life-styles of phyto-
seiid mites and their roles in biological control. Annu.
Rev. Entomol. 42: 291-321.
Mitchell, R. 1973. Growth and population dynamics of a
spider mite {Tetranychus urticae K., Acariña: Tetranychi-
dae). Ecology 54: 1349-1355.
Mossler, M. A., and O. N. Nesheim. 2003. Strawberry pest
management strategic plan. Valrico, F'L. University of
Florida IFAS Extensión, Gainesville, FL.
Oatman, E. R,, F. E, Gilstrap, and V. Voth. 1976. Effect of
different reléase rates of Phytoseiulus persimilis (Acariña:
Phytoseiidae) on the twospotted spider mite on straw-
berry in southern Caflfornia. Entomophaga 21: 269-273.
Oatman, E. R., J, A. McMurtry, F. E. Gilstrap, and V. Voth.
1977a. Effect of Amblyseius califomicus, Phyto.seiulus per-
similis, and Typhlodromus occidentalsi on the twospotted
spider mite on strawberry in southern California. J. Econ.
Entomol. 70: 45-47.
Oatman, E. R., J. A. McMurtry, F. E. Gilstrap, and V. Voth.
1977b. Effect of releases of Amblyseius califomicus on the
twospotted spider mite on strawberry in southern Cali-
fornia. J. Econ. Entomol. 70: 638-640.
Oatman, E. R., J. A. McMurtry, H. H. Shorey, and V. Voth.
1967. Studies on integrating Phytoseiulus persimilis re-
leases, cliernical appflcations, cultural manipulations, and
natura! predation for control of the two-spotted spider
mite on strawberry in southern California. J. Econ. En-
lomo!. 60: 1344-1351.
Oatman,E.R.,J. A. McMurtry, and V. Voth. 1968. Suppres-
sion of the two-spotted spider mite on strawberry with
mass releases of Phijtoseiulus persimilus. J. Econ. Enlomo!.
61: 1517-1521.
Port, C. M., and N.E.A. Scopes. 1981. Biological control by
predatory mites {Phytoseiulus persimilis Alhias-Henriot)
of red spider mite {Tetranychus urticae Koch) infesting


1298
JOLTíNAL OF Economic Entomology
Vol. 99, no. 4
strawberries grown in 'wa!k-in' plástic tunnels. Plant
Pathol. 30: 95-99.
Price, J. 2002. New Acramite®50WS miticide now available.
University of Florida. Institute of Food and Agricultura!
Sciences Ext. iNewsl. Berry/Vegetable Times 7: 1-2.
Sanees, F. V., N. C. Toscano, E. R. Oatman, L. F. Lapre, M. W.
Johnson, and V. Voth. 1982. Reductions in plant pro-
cesses by Tetranychus urticae (Acariña: Tetranychidae)
feeding on strawberry. Environ. Entomol. 11: 733-737.
Sanees, F. V., J. A. Wyman, I. P. Ting, R. A. Van Steenwyk,
and ¥,. R. Oatman. 1981. Spider mite infestations with
photosynthesis, transpiration and productivity of straw-
berry. Environ. Entomol. 10: 442-448.
SAS Institute. 2002. The SAS system 9.0 for Windows. SAS
Instituto, Cary, NC.
Trumble, J. T., and J. P. Morse. 1993. Economics of inte-
grating the predaceous mite Phyto.seiulus perimilis (Acari:
Phytoseiidae) with pesticides in strawberries. J. Econ.
Entomol. 86:879-885.
Waite, G. K. 1988. Integrated control of Tetranychus urticae
in strawberries in south-east Queensland. Exp. Appl. Ac-
arol. 5: 23-32.
White, J. C. 2004. Developing IPM strategies for control of
twospotted spider mites in strawberries in north-central
Florida. M.S. thesis. University of Florida, Gainesville, FL.
White,J.C.,ando. E. Liburd. 2005. Effects of soil moisture
and temperature on reproduction and development of
twospotted spider mite (Acari: Tetranychidae) in straw-
berries. J. Econ. Entomol. 98: 154-158.
Received 22 September 200.5; accepted 2 Marcli 2006.