HOETICI LTL PAL ENTONIOU)GYY
Comparison of Neonicotinoid Insecticides for Use with Biodegradable
and Wooden Spheres for Control of Key Rhagoletis Species
(Diptera: Tephritidae)
LUKASZ L. STEllINSKI, OSCAR E. LIBURD,' STARKER WRI( t,'I2, RONALD J. PROKOPY,2
ROBERT BEHLE,3 AND MICHAEL R. McGUIRE4
Department of Entomology, Center for Integrated Plant Systems, Michigan State University, East Lansing, MI 48824
J. Econ. Entomol. 94(5): 1142-1150 (2001)
ABSTRACT Field-based studies and laboratory bioassays were conducted with apple maggot,
S .. ..... (Walsh), and blueberry maggot, Rhagoletis mendax Curran, flies to investigate
the performance and duration of activity of insecticide-treated biodegradable and wooden spheres
for control of Rhagoletis species. Four neonicotinoid insecticide treatments including imidacloprid,
thiamethoxam, and thiocloprid at 2% (AI) were evaluated with biodegradable spheres. In 1999,
.. .. more apple maggot flies were found killed by imidacloprid-treated spheres compared
with thiamethoxam-treated spheres during early and late season. In 2000, spheres treated with either
of two formulations of imidacloprid killed significantly more apple maggot flies compared with
thiamethoxam, thiocloprid, and untreated spheres. In blueberries, there were no significant differ-
ences between the numbers of blueberry maggot flies killed by both imidacloprid-treated or
thiamethoxam-treated spheres in 1999. However, during the 2000 blueberry field season, both
formulations of imidacloprid were significantly more effective in killing blueberry maggot flies
compared with spheres treated with thiamethoxam, thiocloprid and untreated controls. Overall,
spheres treated with thiocloprid were ineffective and did not kill i.:iil .nh', more apple maggot
or blueberry maggot flies compared with the controls. Laboratory bioassays showed that the
effectiveness of field-exposed spheres treated with imidacloprid at 4 and 8% (AI) and thiamethoxam
at 4% (AI) in I .:1,. apple maggot flies was not ,.. t .I.. reduced over a 12-wk aging period.
Additionally, wooden spheres aged outdoors for 12 wk with and without mold maintained residual
activity in laboratory tests, whereas biodegradable spheres of equal aging, with and without mold
lost their effectiveness in killing apple In other studies, we confirmed that the addition
of an external feeding stimulant (sucrose) .,. ,. ...i increases the effectiveness of both biode-
gradable and wooden spheres treated with imidacloprid at 2% (AI).
KEY WORDS '; ,- :.. "i mendax, insecticide-treated spheres
THE APPLE MAGGOT, IJ..._ ... ,. : .'. !. '(Walsh), and
the blueberry maggot, Rhagoletis mendax Curran, are
the most important late-season insect pests of apples,
Malus donmestica Borkhausen, and blueberries, Vac-
cinint spp., respectively, in the northeastern and mid-
western United States (Liburd et al. 1999). Sexually
mature flies responding to visual and olfactory stimuli
migrate into apple orchards and blueberry plantings
and subsequently oviposit into ripening host fruit. The
larvae develop inside the fruit rendering it unmarket-
able. To prevent fruit injury, commercial growers
commonly apply an organophosphate insecticide ev-
ery 10 14 d once the adult flies are active (Stanley et
1 Department of Entomology and Neimatology, University of Flor-
ida, Cainesville, FL 32611. E-mail: liburd@.rrsu.edu
2Department of Entomology, University of Massachusetts, Am-
herst, MA 01003.
National Center for Agricultural Utiliation Research, Bioactive
Agents Research Unit, Agricultural Research Service, USDA, Peoria,
IL 61604.
4 Shafter Research and Extension Center, 17053 Shafter Avenue,
Shafter, CA 93263.
al. 1987, Agnello et al. 1990, Liburd et al. 1998a).
Because of increasing restrictions on the use of broad-
spectrum insecticides, resulting from Food Quality
Protection Act (FQPA) regulations, the development
of effective alternatives for management of key Rhago-
letis species is of much importance to the fruit indus-
try.
The literature documenting behavioral manage-
ment techniques for apple maggot is voluminous
(Prokopy 1975, Reissig et al. 1985, Prokopy and Mason
1996. Reynolds and Prokopy 1997). Kring (1970) eval-
uated several trap types and demonstrated that un-
baited yellow panels with red hemispheres were ef-
fective in attracting apple maggot flies even at low
population densities. Later, Reissig et al. (1985)
showed that sticky red spheres (8.5 cm diameter)
baited with synthetic apple volatiles were four times
more effective than unbaited red spheres. Recently,
Zhang et al. (1999) showed that a mixed blend con-
sisting of butyl butanoate (10%), propyl hexanoate
(4%), butyl hexanoate (37%), hexyl butanoate (44%),
and pentyl hexanoate ( ) used as bait attractant was
0022-0493/01/1142-1150$02.00!0 c 2001 Entomological Society of America
STELINSKI ET AL.: NEONICOTINOID-TREATED SPHERES ON Rhagoletis SPECIES
significantly better in attracting apple maggot H'. .
than the recently adopted butyl hexanoate alone.
Their findings were supported by recent studies con-
ducted in Michigan (L.L.S. and O.E.L., unpublished
data), producing similar results using the same blend
of mixed apple volatiles.
Considerable work has also been done on improving
monitoring techniques for the R. pomonella species
group (Prokopy 1977, Prokopy and Hauschild 1979,
Liburd et al. 1998b). In blueberries, Pherocon AM
yellow sticky panels (Great ILakes Integrated Pest
Management [IPM], Vestaburg, MI) are the most
common monitoring devices used by growers for tim-
ing the emergence of '. .ii immature blueberry
maggot flies (Prokopy and Coli 1978, Liburd et el.
1998a). However, recent evidence has suggested that
baited green or red sticky spheres can be used for
monitoring sexually mature blueberry maggot flies
(Liburd et al. 1998a, Liburd and Stelinski 1999). Al-
though such monitoring devices .11 more accurate
timing of insecticide sprays, traps coated with sticky
Tangle-Trap (Tanglefoot, Grand Rapids, MI) can be
inefficient and costly (Prokopy et al. 1990, Liburd et:
al. 1999).
Recently, a nonstick, imidacloprid-treated, biode-
gradable sphere has been shown to be effective in
killing apple maggot (Hu et al. 1998, Liburd et al. 1999)
and blueberry .... i (liburdetal. 1999). Rhago-
letis flies foraging for suitable host plants are attracted
to baited, insecticide-treated spheres for mating and
oviposition (Liburd et al. 1999). Flies landing on these
spheres die after consuming a lethal dose of insecti-
cide. As discussed in Liburd et al. (1999), the use of
biodegradable spheres offers several advantages over
conventional trapping using sticky traps or insecticide
spray applications, including the potential for season-
long control of fruit flies by a single deployment of
spheres at the onset of the season, a possible reduction
of insecticide residues on the fruit, and a reduction in
labor costs.
In field studies, Liburd et al. (1999) caught 25 times
as many apple maggot and four times as many blue-
berry maggot flies on Plexiglas panes placed beneath
biodegradable spheres treated with imidacloprid
(Provado 1.6 F, Bayer, Kansas City, MO) compared
with untreated (control) spheres. Further studies
showed that the mean time that flies spent on imrida-
cloprid-treated spheres was significantly longer than
on untreated spheres. Most recently, Hu et al. (2000)
achieved season long residual activity with 80% fly kill
in laboratory assays after weathering spheres treated
with imidacloprid (Merit 75 WP, Bayer) at 1.5% (Al)
in an orchard for 3 io. However, there are no studies
on the effectiveness of the insecticides thiamethoxamr
(Actara, Novartis, Greensboro, NC) or thiocloprid
(Calypso, I on apple maggot :"i and only one
recent paper (Ayyappath et al. 2000) has discussed the
effects of thiamethoxam but not thiocloprid on blue-
berry maggot flies using insecticide-treated sphere
technology.
As FQPA regulations lead to a reduction in the use
of organophosphate insecticides, and public pressure
against the use of broad-spectrum insecticides in-
creases, it becomes necessary to .. .1. effective
nonorganophosphate insecticides for inclusion into
novel pest management tactics. The objective of this
study was to investigate the duration and '.-.. -.
of activity of biodegradable and wooden spheres
treated with the neonicotinoid insecticides imidaclo-
prid (Provado 1.6 F and Merit 75 WP), thiamethoxam
(Actara), and thiocloprid (Calypso) on apple maggot
and blueberry maggot flies.
Materials and Methods
Field experiments to determine the effectiveness of
biodegradable, neonicotinoid-treated spheres in kill-
ing apple maggot and blueberry maggot flies were
conducted in commercial apple orchards and blue-
berry plantings in southwestern Michigan during the
1999 and 2000 field seasons. Laboratory bioassays eval-
uating the effects of sphere aging, insecticide treat-
ment, and feeding stimulant on R. pomonella using
both biodegradable and wooden spheres were carried
out at the University of Massachusetts, Amherst, MA,
in 1999.
Biodegradable spheres (9 cm diameter) made from
a combination of sugar, starch, and flour were ob-
tained from the United States Department of Agricul-
ture (USDA) laboratory in Peoria, IL. : ... ... .
for sphere preparation were described in Liburd et al.
(1999). i 1:. I1 spheres consisted of a mixture of
water (150 g), sucrose (360 g), high fructose corn
syrup (330 g), pregelatinized corn i. o (630 g). cay-
enne pepper (14.7 g), and sorbic acid (1.5 g). Before
deployment in the field, spheres were brush-painted
with a mixture containing DevFlex latex paint (ICI
Paints, Cleveland, OI) (70%), sucrose feeding stim-
ulant (20%). water (8%), and insecticide at 2% (AI).
Wooden, 9-cm-diameter spheres used in Massachu-
setts bioassays were painted in the same manner as the
biodegradable spheres. Spheres were painted red for
apple maggot experiments and green for blueberry
maggot experiments.
Michigan. Field Evaluation of Neonicotinoid-
Treated Spheres. The experimental designs were com-
pletely randomized blocks (blocked by apple varieties
and blueberry cultivars) with four replications. In
apples, spheres were spaced 20 m apart within blocks
(25 m between blocks) and were hung 1.5 m above
ground within the canopy of 'Red Delicious' and
'Golden Delicious' trees. Spheres were positioned
0.25-0.5 m from fruit and foliage according to the
guidelines suggested by Drummond et al. (1984). All
biodegradable spheres used in apple maggot experi-
ments were baited with polyethylene vials (Israel
Andler and Sons, Evrett, MA) containing 4 ml of butyl
hexanoate (Penta International Corporation, West
Caldwell, NJ).
In blueberries, biodegradable spheres were hung
within the canopy of lI... i:. and Jersey blueberries
at a height 15 cm below the tops of blueberry bushes
according to the recommendations of Liburd et al.
(2000). Biodegradable spheres used in blueberry mag-
October 2001
JOURNAL OF ECONOMIC ENTOMOLOGY
got experiments were baited with polycon dispensers
(Great ILakes IPM) containing 5 g of ammonium ac-
etate (Liburd et al. 1998a).
Apple Maggot (1999). Three treatments were eval-
uated that included the: ii ._, (1) spheres treated
with imidacloprid (Provado 1.6 F), (2) spheres treated
with thiamethoxam (Actara), and (3) untreated con-
trol spheres. The number of apple maggot flies killed
was assessed using Plexiglas panes (60 by 45 cm)
coated with sticky, aerosol-formula Tangle-Trap and
placed horizontally 30 crcm below each sphere
(Liburd et al. 1999). Killed apple maggot flies were
counted by sex and removed from panes twice per
week. Data on the number of apple maggot 1.. killed
were separated into four monitoring periods to 11 i)
the seasonal abundance of apple maggot flies in Mich-
igan (Howitt 1993) and to provide even comparisons
with laboratory assays. During the first monitoring
period (8-19 July), flies were beginning to emerge.
The second (22 July-2 August) and third (5-16 Au-
gust) monitoring periods constituted peak fly activity,
depending on the predominant apple varieties within
the area. During the final monitoring period (19 Au-
gust-9 September), fly populations were in decline.
Apple Maggot 2000. During our 2000 field season,
three treatments from our 1999 apple maggot study
were selected for further investigation. Two new neo-
nicotinoid treatments, thiocloprid (Calypso) and an-
other formulation of imidacloprid (Merit WP 75)
were included in our 2000 evaluation of spheres.
Spheres were prepared according to the previously
described protocol and all insecticide concentrations
were prepared at 2% (Al). The Merit WP 75 formu-
lation was prepared as a slurry by mixing the wettable
powder with distilled water before mixing this insec-
ticide with paint. The number of apple maggot flies
: I. 1 was assessed in the same manner as described
for 1999. Field data collected in 2000 were not com-
pared with laboratory assays. Therefore, data in 2000
were not divided into separate monitoring periods.
The numbers of apple maggot flies killed over the
course of the entire season were compared to deter-
mine the most effective insecticide treatment.
Blueberry Maggot (1999). Field experiments to com-
pare the effectiveness of imidacloprid and thiame-
thoxam in blueberry plantings paralleled our apple
maggot studies. The three treatments evaluated in-
cluded the :- i. .... (1) spheres treated with imida-
cloprid (Provado 1.6 F), (2) spheres treated with
thiamethoxam (Actara), and (3) untreated control
spheres. The number of blueberry maggot flies killed
was assessed twice per week using the Plexiglas pane
monitoring system described in our apple maggot ex-
periments. Blueberry maggot fly data were separated
into two distinct monitoring periods to coincide with
the seasonal abundance of blueberry maggot flies in
Michigan (Liburd and Stelinski 1999).
Blueberry Maggot 2000. Our blueberry maggot fly
experiment in 2000 likewise ... .1I. :.. the 2000 apple
maggot study. Five treatments were evaluated in-
eluding the I i: .- (1) imidacloprid (Provado),
(2) imidacloprid (Merit WP 75) (3) thiamethoxam
(Actara), (4) thiocloprid (Calypso), and (5) un-
treated spheres (control). All insecticide treatments
were prepared at 2% (Al). The number of blueberry
maggot flies killed was assessed using Plexiglas panes
as described for the 1999 apple experiment. Treat-
ments were compared by using total numbers of blue-
berry maggot flies found killed over the course of the
entire season.
Massachusetts Laboratory Bioassays. In 1999, we
conducted two laboratory bioassays in Almherst, MA,
to determine the effectiveness and residual activity
of biodegradable and wooden spheres in killing
apple maggot flies. The first assay was conducted to
compare three different concentrations (2, 4, and
8% [AI]) of imidacloprid (Provado 1.6 F) and thia-
methoxam (Actara) on wooden spheres. The second
assay was developed at standard active ingredients
(2%) to compare wooden spheres with biodegradable
spheres with respect to field exposure, mold develop-
ment, presence of external feeding stimulant, and ro-
dent feeding.
Bioassays were conducted with 10 female flies per
treatment and each assay was replicated three times.
Apple maggot flies were reared from larvae that were
collected from apples of unsprayed trees in Amherst,
MA. Flies were maintained in aluminum screen-
Plexiglas cages (30 by 30 by 30 cm) and supplied with
water and food strips consisting of filter paper 5 by
7 cm dipped in a solution of enzymatic yeast hydro-
lysate and sucrose (1:3) and dried 24 h before use. All
females used in bioassays were sexually mature
(14 20 d of age) and deprived of food, but not water,
10 h before testing (Hu et al. 2000). Spheres used in
our aging experiment were hung in commercial apple
orchards under natural environmental conditions and
were retrieved from the field for laboratory bioassays
at appropriate aging intervals (3, 6, 9. and 12 wk).
,Il -, : sets of spheres were used for each interval.
For baseline toxicity tests, "0 wk" nonagedd) spheres
were also prepared.
Performance of Two Neonicotinoids at Various Per-
centages of Active Ingredients. Spheres used in bioas-
says were prepared according to the protocol de-
scribed earlier and painted with DevFlex latex red
paint. Seven treatments were used in our first bioassay.
The first three treatments consisted of spheres treated
with imidacloprid (Provado 1.6 F) at 2, 4, and 8% (Al).
Treatments 4, 5, and 6 consisted of spheres treated
with thiamethoxam (Actara) at the same concentra-
tions (2, 4, and 8% [AI]). The seventh treatment was
a sphere without insecticide. Randomly selected, sex-
ually mature females were transferred using 35-ml
plastic cups onto single treated spheres hung from the
ceiling of Plexiglas cages (30 by 30 by 30 cn). Flies
were I:1 .I to feed for 10 min or until they fell off
of spheres. After exposure to sphere treatments, flies
were removed from cages and 1'I I. h i1, .i ...i
plastic cups with food and water. Observations to
determine mortality were made at intervals of 24, 48,
and 72 h.
i of Aging, Feeding Stimulant, and Fungal
Growth on bnidacloprid-Treated Spheres. Our second
Vol. 94, no. 5
STELINSKI ET AL.: NEONICOTINOID-TREATED SPHERES ON Rhagoletis SPECIES
Table 1. Effect of neonicotinoid-treated spheres on apple maggot fly, Michigan (1999)
Sphere atmnts 1st monitoring period 2nd monitoring period 3rd monitoring period 4th monitoring period Tota
Sphere treatments season
8/7 19/7 227 2/8 5/8 16/8 19/8 9/9 8/7 9/9
Inidacloprid-treated 98.8 21.1a 63.3 1 16.1a 48.0 1 9.0a 36.8 4.8a 280 52.8a
(Provado 1.6 F)
Thiomethoxam-treated
(Actara)
Untreated (control)
31.0 6.1b
4.0 + 3.0e
33.3 3.0a
8.3 7.0b
42.5 9.6a
2.0 1.4lb
12.5 0.9b 119.3 b 10.6b
1.0 0.0c 15.3 11.3c
Mean SEM number of flies found killed on Plexiglas. Means within the same column followed by the same letter are not significantly
different (P = 0.05, LSD test).
laboratory assay was designed to investigate the irm-
pact of aging, feeding stimulant, and mold growth on
the effectiveness of spheres treated with imidacloprid
(Provado 1.6 F) and thiamethoxam (Actara). at 2%
(AI). Fourteen treatments were evaluated. The initial
seven treatments had a sucrose feeding-stimulant
(20% sucrose/water solution) ..;1;. .1 to their external
surface after exposure to external environmental con-
ditions and just before carrying out the assay. The
treatments included the following: (1) wooden
spheres exposed outdoors for 12 wk with no growth of
mold, (2) wooden spheres exposed outdoors for 12 wk
with 90% of their surface area covered with mold, (3)
wooden spheres not exposed outdoors, (4) biodegrad-
able spheres exposed outdoors for 12 wk with no mold
cover, (5) biodegradable spheres exposed outdoors
for 12 wk with 90% of their surface area covered with
mold, (6) biodegradable spheres not exposed out-
doors, and (7) biodegradable spheres exposed out-
doors for 12 wk and having 50% of their mass eaten by
rodents. Treatments 8 14 were identical to the pre-
viously described seven treatments; however, these
lacked the application of the sucrose feeding-stimu-
lant on their outer coating before the assay. The assay
:. i' I the same protocol as described for the first
with respect to rearing and handling of apple maggot
flies.
Statistical Analysis. Data from all experiments were
square-root transformed (x + I ) and then subjected
to an analysis of variance. Means were separated by
least significant .bt.-. .. (L,SD) (P = 0.05) (SAS
Institute 1989). The untransformed means and stan-
dard errors are presented in tables and figures.
Results
Field-Based Evaluation of Neonicotinoid-Treated
Spheres. During our 1999 apple maggot study, signif-
icantly (F = 35.8; df = 2, 6; P < 0.01) more apple
maggot flies were found killed over the entire season
on Plexiglas panes hung beneath biodegradable
spheres treated with imidacloprid (Provado 1.6 F)
compared with spheres treated with thiamethoxam
(Actara) (Table 1). Both imidacloprid and thiamre-
thoxam-treated spheres killed ... ..i .. .... i'
maggot flies compared with control (untreated)
spheres (Table 1). The number of apple maggot flies
Iii .1 by imidacloprid-treated and thiamethoxam-
treated spheres averaged -18 and -8 times more,
respectively, than the number killed by untreated
spheres (Table 1).
As the growing season progressed, we noticed
changes in the effectiveness of imidacloprid and thia-
methoxam-treated spheres based on Plexiglas trap
data. During the first monitoring period (8 19 July),
werec(...1. .1 ..1, : (F= 26.4;df = 26; P< 0.01)
more apple maggot flies on Plexiglas panes hung be-
neath imidacloprid-treated spheres compared with
thiamethoxam-treated spheres (Table 1). During the
second and third monitoring periods, there were no
significant differences in the number of killed apple
maggot flies beneath spheres treated with either in-
secticide (imidacloprid or thiamethoxam) (Table 1).
During the fourth monitoring period, again signifi-
cantly more apple maggot flies were killed by imida-
cloprid-treated spheres compared with thiame-
thoxam-treated spheres (Table 1).
The results of our second year's apple maggot study
showed no significant differences in the number of
killed apple maggot flies beneath spheres treated with
either formulation of imidacloprid (Provado 1.6 F or
Merit 75 WP) (Table 2). However, biodegradable
spheres treated with either formulation of imidaclo-
prid (Provado 1.6 F and Merit 75 WP) killed signifi-
cantly (F = 54.9; df = 4, 12; P < 0.001) more apple
maggot I.. than other treatments tested (Table 2).
There was no significant difference in the number of
dead apple maggot flies beneath spheres treated with
Table 2. Comparison of neonicotinoid insecticides at 2%
active ingredients using biodegradable spheres for control of apple
maggot, Michigan (2000)
Mean
SEM no.
Sphere treatments killed apple
maggot flies
26/6 11/8
hnidacloprid-treated (Provado 1.6 F) 182.8 13.6a
Imidacloprid-treated (Merit 75 WP) 190.0 35.7a
Thiomethoxam-treated (Actara) 76.3 8.6b
Thiocloprid-treated (Calypso) 10.8 2.8c
Untreated (control) 98 1.5c
Mean I SEM number of flies found killed on Plexiglas. Means
within the same column followed by the same letter are not signifi-
cantly different (P = 0.05 LSD test).
October 2001
JOURNAL OF ECONOMIC ENTOMOLOGY
Table 3. Effect of neonicotinoid-treated spheres on blueberry maggot fly, Michigan (1999)
Sphere treaents st monitoring period 2nd monitoring period Total season
16/7-22/7 28/7-6/8 16/7-6/8
Imidacloprid-treated 99.8 17.2a 52.3 1 9.9a 133.5 1 30.4a
(Provado 1.6 F)
Thiomethoxam-treated 71 3 34.0a 27.5 1 1.9a 127.3 43 5a
(Actara)
Untreated (control) 12.3 3.8b 3.5 1.8b 15.8 l 5.0b
Mean SEM number of flies found killed on Plexiglas. Means within the same column followed by the same letter are not significantly
different, (P = 0.05, LSD test).
ihiocloprid (Calypso) and our untreated (control)
spheres (Table 2).
The results from our 1999 blueberry field experi-
ments were different from those observed for apples.
There were no significant differences between the
number of killed blueberry maggot i.. found on
Plexiglas panes hung beneath spheres treated with
either imidacloprid or thiamethoxam over the course
of the season (Table 3). Also, there was no rt o ,
1. 1 .. in the number of flies killed between imi-
dacloprid and thiamethoxam-treated spheres in either
first or second monitoring periods (Table 3). How-
ever, we recorded significantly (F = 32.4; df = 2, 6 P <
0.01) more killed blueberry maggot flies on Plexiglas
panes placed beneath treated spheres compared with
untreated spheres (Table 3).
Our second year's blueberry maggot results were
similar to those observed in our apple maggot 2000
field studies. There were no significant 1,ll .. .in
the number of blueberry maggot flies killed by either
Provado 1.6 F or Merit 75 WP (Table 4). However,
both imidacloprid treatments killed significantly (F =
53.2; df = 4. 12: P < 0.001) more blueberry maggot flies
compared with spheres treated with thiamethoxam
(Actara) (Table 4). On average, imidacloprid-treated
spheres killed 2.3 times as many flies compared with
spheres treated with thiamethoxam (T .I .i !). Finally,
spheres treated with thiocloprid (Calypso) did not kill
significantly more blueberry maggot flies compared
with control spheres (Table 4).
Performance of Two Neonicotinoids at Various Per-
centages of Active Ingredients. In our 1999 sphere
aging experiments, the cumulative rainfall exposures
Table 4. Comparison of neonicotinoid insecticides at 2%
active ingredients using biodegradable spheres for control of
blueberry maggot flies, Michigan (2000)
Mean
SEM no.
killed
Sphere treatments blede
blueberry
maggot flies
26/6 11/8
lnidacloprid-treated (Provado 1.6 F) 512.0 78.5a
Imidacloprid-treated (Merit 75 WP) 449.3 72.0a
Thiomethoxam-treated (Actara) 216.3 47.7b
Thiocloprid-treated (Calypso) 121.5 8.6c
Untreated (control) 93.8 19.9c
Mean I SEM number of flies found killed on Plexiglas. Means
within the same column followed by the same letter are not signifi-
cantly different (F = 0.05, LSD test).
of spheres after each aging interval were 0.0, 3.6, 5.3,
15.5, and 43.2 cm at 0, 3, 6, 9, and 12 wk of exposure,
respectively. We recorded no significant differences
in the number of apple maggot flies I li. I by newly
prepared spheres and spheres that were aged for 3 wk
and treated with either imidacloprid or thiamethoxam
at any of the percentages of active ingredients tested.
However, all neonicotinoid-treated spheres killed sig-
nificantly (F = 19.3; df = 6, 12; P < 0.001) more flies
compared with the controls (Fig. 1). The effectiveness
of aged imidacloprid-treated spheres at rates of four
and 8% (AI) did not decrease ,. -..i ,..: i ,
the aging period (Fig. 1). However, there was a sig-
nificant decrease in the .. .... .. ..... .
treated spheres at 2% (AI) at 12 wk of aging outdoors
compared with shorter aging periods (Fig. 1). Similar
to imidacloprid-treated spheres, there was no signif-
icant decrease in the performance of thiamethoxam-
treated spheres at 4% (AI) throughout the 12-wk aging
100 -
80 -
60-
40-
20
0-
a 100-
80-
60-
S40-
i 20-
a
2% AI
0 3 6 9 12
-L1----
4 %AI
- Imidaclopnd
-0- Thiomethoxam
-A-Control
0 ] I ---
0 3 6 9 12
00
80 ... ......
80 -.4
60 8 % AI
40
20
0- --
0 3 6 9 12
Weeks
Fig. 1. Percentage mortality of apple maggot flies ex-
posed to imidacloprid and thiamethoxam-treated spheres
with varying percentage of active ingredients subjected to 3,
6, 9, and 12 wk of field aging.
Vol. 94, no. 5
CL
STELINSKI ET AL.: NEONICOTINOID-TREATED SPHERES ON Rhagoletis SPECIES
loo 0 an
ab
S80- bc bc bc
0
o
E cd cd
2 60 -
o I
GF
20 -
A B C D E F G A B C D E F G
1 1 1 1 1 1 1 2 2 2 2 2 2 2
Fig. 2. Percentage mortality of apple maggot flies exposed to imidacloprid-treated spheres at 2% (AI) of varying
composition, age, and mold coverage. Bars representing means that are labeled with the same letter are not significantly
different, (P = 0.05, LSD test). (A) Wooden spheres exposed 12 wk with no mold. (B) Wooden spheres exposed 12 wk with
90% mold coverage on surface. (C) Wooden spheres not exposed outdoors. (D) Biodegradable spheres exposed 12 wk with
no mold. (E) i 1 i- 1.1 spheres exposed 12 wk with 90% mold coverage on surface. (F) Biodegradable spheres not
exposed outdoors. (G) Biodegradable spheres exposed 12 wk with 50% of mass eaten by rodents. (1) Sphere with sucrose
feeding stimulant added before testing. (2) Spheres without sucrose feeding stimulant added before testing
period. However, when the active ingredient was low-
ered to 2%, thiamethoxam-treated spheres killed sig-
nificantly fewer flies at 12 wk compared with shorter
aging periods. In addition, thiamethoxam-treated
spheres at the higher rate of 8% (AI) killed fewer apple
maggot flies at the 9- and 12-wk aging intervals corm-
pared with the shorter aging periods. Spheres treated
with either insecticide at all of the rates tested killed
,,,i :.ii, (P < 0.001) more flies compared with
control spheres at every aging interval (Fig. 1).
i !!,... of Aging, Feeding Stimulant, and Fungal
Growth on Imidacloprid-Treated Spheres. All biode-
gradable and wooden sphere treatments exposed out-
doors with 20% sucrose (feeding stimulant) killed sig-
.,,f; .. ..i (F = 19.8; df = 13, 26 P < 0.001) more apple
maggot I. compared with spheres that lacked such
an application of sucrose (Fig. 2). There was no sig-
nificant I .1. .. in mortality of apple maggot flies
between biodegradable and wooden spheres before
aging (Fig. 2). There was a -.. i.. --. (P < 0.001)
decrease in the number of apple maggot flies killed by
biodegradable spheres containing feeding stimulant
that were aged outdoors for 12 wk compared with
unexposed biodegradable spheres, although such de-
crease was not observed for wooden spheres after
exposure for 12 wk (Fig. 2). The effectiveness of both
biodegradable and wooden spheres that were exposed
outdoors for 12 wk and with 90% mold cover was not
statistically different from spheres of equal aging with
no fungal mold. Biodegradable spheres that had 50% of
their mass removed by rodent feeding killed signifi-
cantly (P < 0.001) fewer apple maggot flies compared
with unexposed biodegradable spheres. However, the
rodent-damaged biodegradable spheres 111.. I statis-
tically equal numbers of apple maggot 1 .. to undam-
aged biodegradable spheres that were exposed out-
doors for 12 wk with and without 90% mold coverage.
(Fig. 2).
Discussion
The study demonstrated that baited, biodegradable
spheres treated with the insecticide imidacloprid, ir-
respective of formulation (Provado 1.6 F or Merit 75
WP), were more effective in killing apple maggot flies
than identical spheres treated with thiamethoxam or
thiocloprid. Upon initial :,. i.l deployment, imidaclo-
prid-treated spheres killed high numbers of apple
maggot :,. but there was a gradual decrease in the
number of :. killed as the season progressed. Alter-
natively, thiamethoxam-treated spheres killed fewer
apple maggot flies initially and the numbers of flies
killed also ..i...ii decreased as the season pro-
gressed. The decreased numbers of dead flies over
time may be due to a number of factors, including loss
of insecticide from sphere coating, aging effects on
spheres, decreasing fly populations in late season, or a
combination of these factors.
During our second (2000) field season, spheres
treated with either formulation of imidacloprid
showed equal effectiveness in killing apple maggot
flies. Thiamethoxam-treated spheres again killed
fewer apple maggot flies than imidacloprid-treated
spheres. Our laboratory bioassays supported field data
by indicating that imidacloprid-treated spheres were
more effective in killing apple maggot flies compared
with thiamethoxam-treated spheres. Spheres treated
with thiocloprid (Calypso), however, were no more
effective than control spheres in the field. We believe
that treating spheres with imidacloprid rather than
thiamethoxam or thiocloprid may result in more ef-
fective control of apple maggot flies in commercial
orchards.
The results from our blueberry ..,.1 .. ,1.1. *
different from those in apples. In 1999, imidacloprid-
and thiamethoxam-treated spheres showed statisti-
.11 equal effectiveness in killing blueberry maggot
throughout the blueberry-growing season. By
contrast, in 2000 imidacloprid-treated spheres per-
October 2001
JOURNAL OF ECONOMIC ENTOMOLOGY
formed better than thiamethoxam-treated spheres
over the course of the season. In 2000, we captured our
first blueberry maggot fly on monitoring traps two
weeks earlier than in 1999. Therefore, all biodegrad-
able sphere treatments were deployed in the field 2 wk
earlier in 2000 (26 June) than in 1999 (July 16). How-
ever, during both years blueberry:... I: .;: -i.
was monitored until the end i : .. (6 August
in 1999 and 11 August in 2000). The longer field ex-
posure of thiamethoxam-treated spheres in 2000 may
have resulted in the greater observed decline in effi-
cacy near the end of that field season, while such a
decline was not observed for imidacloprid-treated
spheres. These results imply that thiamethoxam may
have been lost from biodegradable spheres at greater
rate than imidacloprid. As observed for the apple mag-
got fly, spheres treated with thiocloprid were no more
effective in killing blueberry maggot flies than control
spheres in the field.
Our laboratory bioassays using biodegradable and
wooden spheres provided us with data similar to those
obtained in the field and helped explain some of the
differences and changes in effectiveness that were
observed over the course of the growing season in
Michigan. The assays also showed that the ::. -
ness and period of activity of imidacloprid-treated
spheres could be lengthened by increasing the per-
centage of (AI) ofinsecticide in the spheres above 2%.
Such a change in formulation needs further research
before it can be implemented in commercial apple
orchards. However, increasing the concentration of
(AI) of imidacloprid-treated spheres above 2% may
not be necessary for blueberry maggot fly manage-
ment. The results of our bioassays also showed that 4%
(AI) might be optimal for thiam ethoxam-treated
spheres against the apple maggot fly. Spheres treated
in this manner killed .... i :..,i more apple maggot
: ...,... with similar spheres treated atboth two
and 8% (AI) (Fig 1). It is possible that the 8% (AI)
treatment of thiamethoxam acted as aphago- or tarsal-
deterrent for the apple maggot flies, resulting in lesser
mortality compared with similar spheres treated at 4%o
(AI). The 11,- of insecticide-treated spheres de-
pends on the flies' acceptance of the phago-stimulant
(sucrose) in order for it to imbibe the insecticide.
Therefore, it is crucial that insecticide formulations
and application rates used with insecticide-treated
spheres do not present feeding or tarsal deterrents.
The bioassays indicated that fungal infestation ac-
quired by both biodegradable and wooden spheres
over the course of the growing season does not sig-
nificantly decrease the spheres' effectiveness in killing
apple maggot flies. Such fungal growth was observed
in the field during the fourth monitoring period in
apple orchards in Michigan. The problem of fungal
growth was less apparent in our blueberry field ex-
periments. The shorter sphere deployment period
necessary for control of blueberry maggot flies may
account for the observed differences in fungal growth
on the spheres.
Laboratory assays also showed that biodegradable
spheres treated with imidacloprid at 2% (AI) that
were deployed in the ,.. i I for 12 wk had a decreased
effectiveness compared with unexposed biodegrad-
able spheres treated in a similar manner (Fig. 2). In
addition, biodegradable spheres exposed for 12 wk and
without fungal growth i1 ... similarly to spheres
exposed for 12 wk with fungal growth and bio-
degradable spheres exposed for 12 wk having 50% of
their mass removed by rodents (Fig 2). Such a de-
crease in effectiveness was not observed with wooden
imidacloprid-treated spheres that were exposed in the
:. .l 11 r 12 wk. These results indicate that the decrease
in effectiveness r 1 .. i. .. i :. spheres after 12 wk
of field exposure might not be due to fungal infestation
or rodent damage. However, the results imply that
wooden spheres treated with imidacloprid at 2% (AI)
may retain residual insecticidal activity in the field
longer than biodegradable spheres treated in the same
manner.
Although our assays c *,.... .1 that 50% damaged
biodegradable spheres are not less effective than un-
damaged spheres, the complete loss of spheres in the
field due to animal feeding is a significant problem. In
Michigan, loss i] 1. ..i .: i. spheres due to animal
feeding appeared to be insignificant in 1999 when
-95% of spheres deployed in :;. I.1 studies were re-
trieved at the end of the season. However, in 2000,
-20% : -, -. i ,i = spheres deployed in an aban-
doned apple orchard required replacement one
month after initial deployment because of rodent
feeding. I Ii. i: rodent/animal deterrents must be
developed before biodegradable spheres can be rec-
ommended for commercial use.
Our findings with respect to feeding stimulants
were consistent with the earlier studies of Hu et al.
(1998). The use of a feeding stimulant (sucrose) en-
courages prolonged feeding and increases the poten-
tial for Rhagoletis :i, to ingest a greater dosage of
insecticide. Although aged wooden spheres per-
formed. :,.. 'II. I orbetter than aged biodegradable
spheres in our Massachusetts laboratory studies, pre-
vious field studies have shown that the use of wooden
spheres requires the periodical reapplication of feed-
ing stimulant, because the externally .i. i'.. 1 sucrose
is washed off by rain. Therefore, we still support fur-
ther development and future use of biodegradable
spheres or the development of a constant release su-
crose dispenser to be used with wooden spheres as a
control tactic for key Rhagoletis species.
Overall, both :;. I i and laboratory experiments con-
firmed several crucial requirements that must be met in
order for insecticide-treated spheres to be effective
throughout the growing season. First, they must deliver
a lethal dose of insecticide over the course of the entire
growing season to provide adequate fruit protection.
Second, they must be able to withstand adverse weather
conditions and present a feeding deterrent for rodents.
Future prototypes of biodegradable spheres should in-
clude appropriate anti-fungal agents and rodent-feeding
deterrents.
Recent studies have shown that insecticide-treated
spheres can achieve comparable control of the apple
maggot fly (Propkopy et al. 2001) and the blueberry
Vol. 94, no. 5
STELINSKI ET AL.: NEONICOTINOID-TREATED SPHERES ON Rhagoletis SPECIES
maggot !H (Stelinski and Liburd 2001) to the use
of organophosphate insecticides. This study demon-
strated .', ., i,. 1.1-.. .I .1 imidacloprid-treated spheres
are more effective in killing apple maggot and blue-
berry maggot flies than similar spheres treated with
thiamethoxam or thiocloprid. The study also provided
initial evidence that the use of the neonicotinoid in-
secticide thiocloprid at 2% (AI) with biodegradable
spheres may be an ineffective tactic. Our results
showed that insecticide formulation, percentage of
active ingredients, sphere material ( .^.. ...
wood), and presence of phago-stimulant impacted the
effectiveness of insecticide-treated spheres. Cur-
rently, imidacloprid is the most effective neonicotin-
oid insecticide tested for use with both biodegradable
and wooden spheres against both apple maggot and
blueberry maggot flies. In addition, the increase of
imidaclopid from 2 to 4% (AI) improved the effec-
tiveness of insecticide-treated spheres. Finally, our
results provided initial evidence that wooden spheres
treated with iridacloprid maintain longer lasting in-
secticidal activity than identically treated biodegrad-
able spheres.
Acknowledgments
We thank i .'s Apple Orchard, Dan's blueberry plan-
tation, and the owner of blueberry plantation # 4, who
wished to remain anonymous, for .il -. .. conduct our
experiments. We thank Dan Young for his assistance with
sampling and fieldwork. We are grateful to Bradley Chandler
for conducting laboratory-based assays. We thank John Wise
and the staff at the Trevor Nichols Research Complex for
their valuable assistance on this project. We also acknowl-
edge David I i .- 1 (Fruitspheres, Inc., Macomb, IL) for
providing us with biodegradable spheres to conduct our
research in 2000. The research reported here was supported
by USDA Special Fruit Grant No. 61-4058.
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Received for publication 24 .. I March
2001.
Vol. 94, no. 5
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