Florida Entomologist 86(2)
COMPARISON OF BIODEGRADABLE, PLASTIC AND WOODEN
IMIDACLOPRID-TREATED SPHERES FOR CONTROL OF
RHAGOLETIS MENDAX (DIPTERA: TEPHRITIDAE) FLIES
JON E. HAMILL, OSCAR E. LIBURD AND STEVEN R. ALM1
Department of Entomology and Nematology, Natural Area Drive, University of Florida, Gainesville, FL, 32611
'Department of Plant Sciences, Woodward Hall, University of Rhode Island, Kingston, RI 02881
In experiments comparing biodegradable, plastic and wooden imidacloprid-treated spheres for
control of Rhagoletis mendax Curran, the mean number of flies caught on plexiglas panes be-
low each sphere type was not significantly different for the entire season. However, the mean
time spent by R. mendax flies alighting on biodegradable imidacloprid-treated spheres was
significantly greater (2.6x) than plastic imidacloprid-treated spheres. During 2001, signifi-
cantly fewer larvae were found in blueberries harvested from bushes that had wooden imida-
cloprid-treated spheres hung within the canopy compared with bushes where biodegradable
and plastic imidacloprid-treated spheres were deployed. There was no significant difference
between the number of larvae found in berries picked from bushes where biodegradable or
plastic spheres were deployed. All imidacloprid-treated sphere treatments were found to sig-
nificantly reduce blueberry maggot larval infestation in fruit compared with the control.
Key Words: attractant, imidacloprid-treated sphere, blueberry maggot
En experiments comparando las esferas de plastico y de madera biodegradable y tratadas
con imidacloprid para el control de Rhagoletis mendax Curran, el promedio del numero de
las moscas atrapadas sobre la superficie de "plexiglas" debajo cada clase de esfera no fu6 sig-
nificativamente diferente para la estaci6n complete. No obstante, el promedio del tiempo pa-
sado por mosca de R. mendax encima de las esferas biogradables tratadas con imidacloprid
fu6 significativamente mayor (2.6 veces) que en las esferas plasticas tratadas con imidaclo-
prid. Durante 2001, fueron significativamente encontradas menos larvas sobre las moras
(Vaccinium sp.) cosechadas de arbustos que tenian las esferas de madera tratadas con imi-
dacloprid colgadas dentro del dosel comparados con arbustos donde pusieron esferas de plas-
tico biodegradable y tratadas con imidacloprid. No habia una diferencia significativa entire
el nmmero de larvas encontradas en la frutas cortadas de los arbustos donde habian puestas
las esferas de plastico biodegradable y tratadas con imidacloprid. Se encontraron que todos
los tratamientos de las esferas tratadas con imidacloprid redujieron significativamente la in-
festaci6n de larvas en las frutas comparados con el control.
The potential for using a lure and toxicant sys-
tem to control fruit flies has been examined by sev-
eral researchers. Hanotakis et al. (1991) combined
a food attractant, a phagostimulant, a male sex
pheromone, a female aggregation pheromone, a hy-
groscopic substance (glycerin), and two insecticides
(deltamethrin and dichlorvos) with a trap to control
the olive fruit fly, Bactrocera oleae (Gmelin). Duan
and Prokopy (1995) and Hu et al. (2000) tested
dimethoate, abamectin, phloxine B, diazinon, imi-
dacloprid, azinphosmethyl, methomyl, tralom-
ethrin, malathion, fenvalerate, and carbaryl on
wooden spheres and found that only dimethoate,
malathion and imidacloprid were viable candidates
for incorporation into spheres to suppress apple
maggot, Rhagoletis pomonella (Walsh), activity.
Dimethoate, malathion, and imidacloprid did not
reduce the time of visitation by R. pomonella flies
on treated spheres in field cage studies.
Recently, Ayyappath et al. (2000) evaluated thi-
amethoxam at 2-4% Al in sugar/starch spheres and
found this insecticide to be significantly less effec-
tive than spheres treated with 2% AI imidacloprid.
Wright et al. (1999) determined that regardless of
trap design and pesticide incorporation, several
conditions must exist for spheres to become a via-
ble alternative for control of Rhagoletis flies.
Spheres must be: 1) easy and safe to deploy, 2) as
effective as insecticide sprays, 3) able to endure
throughout the growing season, and 4) maintain
fly-killing power with a very low dose of toxicant.
A recent trap design is a biodegradable sphere
consisting of water, gelatinized corn flour, corn
syrup, sugar, cayenne pepper, and sorbic acid
(Liburd et al. 1999; Stelinski & Liburd 2001). The
biodegradable sphere is coated with a mixture of
70% paint, 20% sucrose solution (wt:vol), 4% imi-
dacloprid (AI), and 6% water. Biodegradable
Hamill et al.: Imidacloprid Spheres for Control of R. mendax
spheres were developed as alternatives to broad-
spectrum insecticides for management of key
Rhagoletis spp. in the northeastern United
States. The benefits of using insecticide-treated
spheres include the reduction of pesticide resi-
dues on crops as well as reduced environmental
and worker hazards.
The purpose of this study was to compare biode-
gradable, plastic, and wooden imidacloprid-treated
spheres to determine the most efficacious sphere
type for preventing blueberry maggot injury. All
previous trap designs, with the exception of the
biodegradable sphere, had focused on using
wooden spheres brush painted with enamel paint
mixed with an insecticide. Using a plastic sphere,
either dipping it into an insecticide/sugar solution
or coating it with a mixture of paint and insecticide
presents a third alternative to previous designs.
MATERIALS AND METHODS
Research plots were located in Rhode Island
and Michigan. In Rhode Island plots were located
at two locations during 2000, a 0.5 ha highbush
blueberry, Vaccinium corymbosum L., planting of
'Patriot', 'Blueray', and 'Jersey' located in North
Kingstown and a 2 ha planting of 'Berkley' and
'Collins' located in West Kingston. In 2001, re-
search was conducted at a 0.3 ha planting of 6 cul-
tivars; 'Bluecrop', 'Bluetta', 'Darrow', 'Earliblue',
'Herbert' and'Lateblue' in Kingston, RI and at a 2
ha planting of'Jersey' located in Holland, MI.
Sphere preparation (2000)
Biodegradable spheres were obtained from the
USDA, National Center for Agricultural Utilization
Research Laboratory in Peoria, Illinois and pre-
pared as described in Liburd et al. (1999). Spheres
were brush painted with a mixture containing 70%
enamel paint (Shamrock Green 197A111, ACE
Hardware, Kensington, IL.), 20% (wt:vol) sucrose
solution, 2% (AI) imidacloprid (Provado 1.6 F, Bayer,
Kansas City, MO), and 8% water.
Plastic spheres (Great Lakes IPM, Vestaburg,
MI) were dipped in a solution containing 946 ml
water, 28 g of Merit 75 WP (imidacloprid) (Bayer,
Kansas City, MO), 189 ml of 20% sucrose solution
(wt:vol), and 22 ml (2 ml of product in 20 ml water)
finished additive of Turbo spreader (Bonide,
Yorkville, NY). This mixture represents 81.6% wa-
ter, 2.4% Merit 75WP (1.8% AI imidacloprid), and
16% (wt:vol) sucrose solution. Spheres were dipped
a total of three times during the growing season.
Three treatments were evaluated in two high-
bush blueberry plantings for control ofR. mendax
in a completely randomized block design with
four replicates. Each block consisted of ten 9-cm
diameter green biodegradable imidacloprid-
treated spheres (treatment 1), ten 9-cm diameter
green plastic imidacloprid-treated spheres (treat-
ment 2), and a section of the block consisting of 30
bushes was left untreated (treatment 3, control).
Spheres, approximately one per three bushes,
were hung about 15-cm from the uppermost bush,
which is the most effective position (Liburd et al.
2000), and baited with ammonium acetate (1 g in
4 ml of water) in a 5 ml scintillation vial (National
Diagnostics, Atlanta, GA). A 45 cm x 45 cm square
of plexiglas spray-coated with Tangletrap (The
Tanglefoot Co., Grand Rapids, MI) was hung 30
cm beneath each of the imidacloprid-treated
spheres and supported by four tie-wires (Liburd
et al. 1999).
During each sampling period, R. mendax flies
that landed on treated spheres were observed for
30 minutes; a total of 54 flies were observed. R.
mendax flies captured on plexiglas panes were
counted and removed twice weekly. In addition to
monitoring fly populations with Plexiglas panes,
R. mendax fly populations were also monitored
twice weekly using 9-cm diameter unbaited green
plastic spheres coated with Tangletrap. Towards
the end of the season, an 8-liter sample of'Patriot'
and 'Blueray' was taken on July 13 and 'Blueray'
and 'Jersey' taken on July 27 from North Kings-
town, RI and placed on screens (0.5 cm mesh) over
clear plastic containers to determine the number
of maggots in fruit (Liburd et al. 1998). The num-
ber of maggots collected into the containers was
counted twice a week to determine the effective-
ness of the sphere treatments. Fruit was not sam-
pled from West Kingston, RI because deer had
damaged the majority of the biodegradable
Sphere preparation (2001)
During 2001, sphere preparation methods dif-
fered from those used in 2000 because additional
research data were available on the deployment
of insecticide-treated spheres.
Biodegradable imidacloprid-treated spheres
were prepared as described in 2000. However, the
active ingredient (AI) was increased to 4% because
Stelinski et al. (2001) had shown that the effec-
tiveness of field-exposed imidacloprid-treated
spheres with 2% AI was significantly reduced over
a 12 wk period whereas spheres treated with 4%
AI were not significantly affected.
Plastic imidacloprid-treated spheres were first
painted with a mixture of 26 ml Provado 1.6F (4%
AI imidacloprid) (Bayer, Kansas City, MO), 87 ml
'Bell Pepper' paint (Pittsburgh Paints, Pitts-
burgh, PA) and 20 ml sucrose solution (5.5 g per
20 ml water = ca. 4.8% of the total mixture). In ad-
dition, a newly developed sucrose cap (Prokopy et
al. unpublished data) was attached to the spheres
to act as a feeding stimulant.
Florida Entomologist 86(2)
In Rhode Island, the same three treatments
(biodegradable and plastic imidacloprid-treated
spheres and control) evaluated in 2000 were re-
evaluated in 2001. In Michigan, a fourth treat-
ment, wooden imidacloprid-treated spheres, was
included in the experimental design. Wooden im-
idacloprid-treated spheres (9-cm) were brush
painted with a mixture of DevFlex latex green
paint (ICI Paints, Cleveland, OH) (70%), sucrose
feeding stimulant (20%), water (6%), and imida-
cloprid (4% AI). Like plastic spheres, wooden
spheres had the sucrose cap attached to act as a
The experimental design was similar to 2000
and consisted of randomized block with four rep-
licates. The placement and position within the
canopy of imidacloprid-treated spheres were the
same as 2000. However, spheres were baited with
polycon dispensers containing 5 g of ammonium
carbonate (Great Lakes IPM, Vestaburg, MI). The
dispensers were attached to the strings used for
hanging spheres. Flies were monitored using the
same Plexiglas pane system used in 2000.
In Michigan, four samples of 100 berries per
replicate (totaling 400 berries per treatment)
were taken July 31 and August 1, 3, and 8. Ber-
ries were then placed over 0.5 cm mesh hardware
cloth to allow larvae to exit the fruit and drop into
containers filled with vermiculite (Liburd et al.
1998). The vermiculite was then sifted and blue-
berry maggot fly puparia were collected and
counted to quantify fruit infestation.
O B ^, ^
Data were analyzed by analysis of variance.
(SAS Institute 1989).
The population ofR. mendax flies at the North
Kingstown, RI site was small, and captures on
plexiglas panes for biodegradable and plastic im-
idacloprid-treated spheres were not significantly
different, except on July 18th (Fig. 1). However,
Plexiglas panes placed under biodegradable
spheres consistently captured more flies than
panes placed beneath plastic spheres. The time
spent by R. mendax flies on biodegradable imida-
cloprid-treated spheres (62.6 12.0 sec) was sig-
nificantly greater (F = 32.5, df = 26, 53; P < 0.01)
than the time spent by flies on dipped plastic
spheres (24.2 24.2 sec).
Data collected using 9-cm diameter, unbaited,
green plastic sticky spheres coated with Tangle-
trap indicated that peak flight activity occurred
on July 4th. No maggots were found in 32 liters of
berries harvested on July 13th and 27th from any
of the treatment blocks including the control. The
data at the West Kingston, RI site could not be an-
alyzed due to the high incidence of deer damage.
In Rhode Island, the mean number of flies col-
lected on plexiglas panes below plastic (35.6
4-Jul 6-Jul 11-Jul 13-Jul 18-Jul 20-Jul 25-Jul 27-Jul Season
Fig. 1. Mean number ofR. mendax flies trapped on plexiglas panes beneath imidacloprid-treated biodegradable
and plastic spheres, North Kingston, RI July 4-27, 2000.
Hamill et al.: Imidacloprid Spheres for Control of R. mendax
16.0) and biodegradable (24.6 11.0) imidaclo-
prid-treated spheres was not significantly differ-
ent for the entire season. Similarly, in Michigan
the mean number of flies collected on Plexiglas
panes below biodegradable (33.8 2.98), wooden
(31.3 4.71), and plastic (26.0 9.06) spheres was
not significantly different for the entire season.
Again, plexiglas panes placed below biodegrad-
able spheres consistently captured more R.
mendax flies than plastic and wooden spheres.
In our fruit infestation counts, significantly
fewer (F = 24.63, df = 3,6, P < 0.01) larvae were
collected from berries that had wooden spheres
deployed in blocks compared with plastic and bio-
degradable spheres (Fig. 2). Overall, the mean
number of larvae found in berries treated with
biodegradable, plastic, or wooden spheres was
significantly lower (F = 24.63, df = 3,6, P < 0.01)
than untreated checks. Berries collected from un-
treated (control) plots had 1.8 times as many lar-
vae compared with other treated plots (Fig. 2). Six
biodegradable imidacloprid-treated spheres were
lost to deer feeding during the 6 weeks of experi-
mentation in Michigan. Peak flight activity for
R. mendax occurred on July 24 as measured with
yellow unbaited sticky boards.
Experiments comparing the effectiveness of
biodegradable, wooden, and plastic imidacloprid-
treated spheres showed no significant differences
in the number of flies trapped on Plexiglas panes.
This is the first study showing the effectiveness of
plastic imidacloprid-treated spheres for suppres-
sion of R. mendax. Previous studies have focused
on the efficacy of wooden and biodegradable
insecticide-treated spheres. Currently, wooden
spheres are not commercially available. Also, pro-
duction of wooden and biodegradable spheres
may be prohibitive since the cost may range be-
tween $2-4 per sphere for either sphere type. In
blueberries, depending on infestation of R.
mendax, it may take as many as 100 spheres per
hectare for effective control.
The variation in sphere preparation through-
out 2000 and 2001 was done to optimize insecti-
cide concentration and formulation as well as to
further develop the feeding stimulant system so
that flies will alight for longer time on treated
spheres. Our data showed that flies spent much
longer time on biodegradable imidacloprid-
treated spheres compared with plastic imidaclo-
prid-treated spheres. However, the fact that lar-
val infestation was not significantly affected
between sphere types may indicate that the dura-
tion of stay on treated spheres to deliver a lethal
dose may not be as important as previously
thought. Insecticide compatibility with treated
spheres and susceptibility of the insect may be
the key factors regulating the effectiveness of in-
Because data from our green sticky sphere
monitoring traps indicated that R. mendax flies
were active throughout the season and flies were
trapped continuously with our Plexiglas trapping
device, it was rather surprising that no larvae
were found in treated and untreated plots at our
North Kingston, Rhode Island site. However, be-
cause the plots were relatively small, it is possible
Wooden Plastic Biodegradable Control
Fig. 2. Mean number of maggots in four samples of 100 berries, Holland, MI (2001).
Florida Entomologist 86(2)
that the ammonium acetate attractant used for
baiting imidacloprid-treated spheres may have
attracted flies from treated and untreated areas
resulting in a high mortality and subsequently
preventing infestation in both treated and un-
treated plots. Liburd et al. (1999) also found that
ammonium lures were effective in attracting R.
mendax flies from within a 5 m radius to insecti-
cide-treated sphere traps.
The biodegradable imidacloprid-treated spheres
used in our study may be more appealing to grow-
ers than the plastic spheres used in 2000. Bio-
degradable spheres did not require additional
maintenance after initial deployment in the field.
However, some of these spheres needed to be re-
placed because rodents and deer frequently ate
them. As Stelinski et al. (2001) stated, prevention
of deer feeding and inhibition of mold growth are
needed before these spheres can be recommended
The plastic spheres used in 2000 needed suc-
cessive dipping in pesticide solution to maintain
their effectiveness in killing R. mendax flies. De-
pending on the insecticide used, the risks of re-
peated exposure to the applicator may not justify
the use of plastic spheres in this manner. The su-
crose caps (Prokopy et al. unpublished) used on
plastic and wooden spheres in 2001 may make
these spheres more appealing to growers.
Wooden pesticide-treated spheres deployed
with a sucrose cap may be another alternative.
We noted that the resulting fruit injury from plots
treated with wooden imidacloprid-treated spheres
was lower than plastic and biodegradable spheres.
The major problem with wooden spheres is that
they are no longer commercially available; a prob-
lem that can be rectified if their usefulness in the
cropping system exceeds production costs.
The sucrose cap included in our experiments in
2001 was designed to last for a longer duration in
the field compared with earlier versions of sucrose
caps. An increase in the duration of available
sugar may have lead to an increase in fly kill over
time. As Stelinski et al. (2001) noted, pesticide-
treated spheres require a constant supply of sugar
to act as a feeding stimulant and be effective.
Further research is needed to determine how
many spheres are needed to treat different fields
possessing varying fly densities. Our results show
that plastic spheres may be a viable option to con-
trol blueberry maggot. However, there should be a
system for releasing a constant supply of sugar
such as the sugar caps used in 2001. In addition
plastic spheres must maintain the residual effi-
cacy of the pesticide.
We thank Charles Dawson, Marsha Browning, Jason
Koopman, Rhiannon O'Brien, and Erin Finn for assis-
tance in collection of data. We also thank Lukasz Stelin-
ski (Michigan State University) for critical review of the
manuscript. In addition we would like to thank David
Bloomberg (Fruitspheres, Inc., Macomb, IL) for provid-
ing biodegradable spheres. This research was supported
by USDA-CSREES Grant No. 721495612. This manu-
script is Florida Agricultural Experiment Station Jour-
nal Series R-09081.
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