STORED-PRODUCT Survival of Stored-Product Natural Enemies in Spinosad-Treated Wheat

1 MICHAEL D. TOEWS AND BHADRIRAJU SUBRAMANYAM

Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506

J. Econ. Entomol. 97(3): 1174Ð1180 (2004) ABSTRACT The survival of stored product insect natural enemies in wheat treated with spinosad was investigated in laboratory and pilot scale experiments. The predator Xylocoris flavipes (Reuter), the warehouse pirate bug, and the parasitoids Habrobracon hebetor (Say), Theocolax elegans (West- wood), and Anisopteromalus calandrae (Howard) were exposed to wheat treated with aliquots of water or spinosad at 0.05Ð1 mg ([AI])/kg. X. flavipes was the only species that survived (92% survival) in spinosad-treated wheat at 1 mg/kg. X. flavipes suppressed populations of immature Tribolium casta- neum (Herbst), the red ßour beetle, by nearly 90% compared with a water-treated control, but 100% suppression of immatures was achieved in wheat receiving spinosad or spinosad ϩ X. flavipes treatments. A 3-mo pilot scale experiment to evaluate T. castaneum suppression in drums holding 163.3 kg of wheat showed that the pest populations increased throughout the study in the control treatment, but peaked after 1 mo in the X. flavipes-treated drums. By comparison, better T. castaneum population suppression was achieved in spinosad or spinosad ϩ X. flavipes treatments. Although X. flavipes can survive and reproduce in spinosad-treated wheat, under our test conditions spinosad alone provided adequate suppression of T. castaneum populations in stored wheat.

KEY WORDS Saccharopolyspora spinosa, stored-product , biological control, natural enemies

SPINOSAD, A COMMERCIAL PESTICIDE based on the fermen- vergens Gue´rin-Me´neville (Coleoptera: Coccinelli- tation products of the bacterium Saccharopolyspora dae); phytoseid mite, Phytoseiulus persimilis Athias spinosa Mertz & Yao, is efÞcacious against several Henriot (Acari: Phytoseiidae); and common green insects associated withstored grain in laboratory lacewing, Chrysoperla plorabunda (Fitch) (Neurop- (Fang et al. 2002a, Toews and Subramanyam 2003) and tera: Chrysopidae). Boucher (1999) reported that spi- Þeld evaluations (Fang et al. 2002b). Spinosad is cur- nosad applied to bell peppers effectively controlled rently labeled for use on vegetable crops, ornamentals, the pepper maggot, electa (Say) (Diptera: and forest trees (Thompson et al. 2000), but not on ), but it did not reduce populations of stored grain. In May 2002, an experimental use permit beneÞcial , including unspeciÞed species of for use on grain at 1 mg([AI])/kg was approved by the Coccinellidae, Chrysopidae, Cecidomyiidae, Syrphi- U.S. Environmental Protection Agency (EPA Exper- dae, Nabidae, and hymenopteran-parasitized Aphidi- imental Use Permit No. 62719-EUP-50) that facilitated dae. Mason et al. (2002) found that spinosad was toxic full-scale Þeld trials withthispesticide on farms in to the parasitoids Trichogramma inyoense Pinto & Oat- Kansas and other states. man (Hymenoptera: Trichogrammatidae) and Micro- The compatibility of low rates of spinosad with plitis mediator Haliday (Hymenoptera: Braconidae). parasitoids of stored product insect pests is unknown. Bret et al. (1997) reported that spinosad was much less In the present investigation, we evaluated the sus- toxic to beneÞcial insects in Þeld crops than synthetic ceptibility of several parasitoids and a predator of pesticides. Schoonover and Larson (1995) reported stored product insect pests to spinosad-treated wheat that spinosad was practically nontoxic to the insidious in the presence and absence of hosts or prey. Addi- ßower bug, Orius insidiosus (Say) (Heteroptera: An- tionally, we determined the effectiveness of spinosad thocoridae); convergent lady beetle, Hippodamia con- in combination witha predator to suppress thered ßour beetle, Tribolium castaneum (Herbst) (Co- This paper reports research results only. Mention of a proprietary leoptera: Tenebrionidae), in hard red winter wheat product name does not constitute an endorsement for its use by stored in 208-liter plastic drums. T. castaneum was used Kansas State University or the United States Department of Agricul- in experiments because the adults are relatively less ture. susceptible than other stored-product insect species 1 Current address: USDAÐARS, Grain Marketing and Production ResearchCenter, 1515 College Ave., Manhattan,KS 66502 (e-mail: to spinosad at 1 mg/kg (Fang et al. 2002a,b; Toews and [email protected]). Subramanyam 2003).

0022-0493/04/1174Ð1180$04.00/0 ᭧ 2004 Entomological Society of America June 2004 TOEWS AND SUBRAMANYAM:SUSCEPTIBILITY OF NATURAL ENEMIES TO SPINOSAD 1175

Materials and Methods Spinosad Toxicity to Natural Enemies. The survival of natural enemies in spinosad-treated wheat was de- Wheat. Hard red winter wheat, previously stored termined in the presence and absence of host insects for 24 mo in a round metal bin at the Kansas State in separate laboratory experiments. In the Þrst exper- University Grain Storage Training Center, Manhattan, iment, each0.95-liter glass jar, Þlled with100 g of KS, was used in tests. Four weeks before use in ex- uninfested wheat, was treated with 100 ␮l of distilled periments, the wheat was fumigated with aluminum water (control) or 100 ␮l of spinosad solution to pro- phosphide (Pestcon Systems, Inc., Raleigh, NC) to kill any live insects. Wheat (Ϸ2 kg) was removed for use vide rates of 0Ð1 mg/kg. Eachnatural enemy by rate in experiments from the bin by using a 1.2-m-long treatment was replicated eight times, and each repli- grain trier (Seedburo Equipment Co., Chicago, IL). cate was treated separately. After adding distilled wa- The dockage content, shrunken/broken kernels, for- ter or spinosad solution to the grain, the jars were eign material, damaged kernels, and total defects of Þtted withwire meshand Þlter paper lids and tumbled wheat, determined following ofÞcial methods (GIPSA for 20 min on a ball-mill roller (Morse Manufacturing 1997), was 0.1, 1.0, 0.3, 0.6, and 1.9% by weight, re- Co., model 200VS, East Syracuse, NY), to ensure uni- spectively. The test weight or bulk density of wheat form insecticide coverage on kernels. Twenty-four was 79.1 kg/hl, and the moisture content was 12.1%. hours after tumbling, 20 adults each of A. calandrae Before use in laboratory experiments, the wheat was (Savannahstrain), H. hebetor, T. elegans, or X. flavipes Ϫ Њ were introduced into untreated- or spinosad-treated frozen for7dat 13 C to kill any insects that survived Њ the fumigation. Moisture content of the wheat used in wheat in a jar. All jars were held at 28 C, 65% RH, and all experiments ranged from 11.7 to 13.3%. a photoperiod of 16:8 (L:D) h. After 24-h exposure, Insects. All natural enemies of stored-product in- natural enemies were separated from the wheat using sects were reared in the laboratory to produce a standard testing sieve with1.68-mm meshopenings sufÞcient numbers of known ages. Cultures of the (No. 12, Seedburo Equipment Co.). Natural enemies Indianmeal moth, Plodia interpunctella (Hu¨ bner) that could walk or ßy when prodded with a Þne cam- (Lepidoptera: Pyralidae), were reared on a turkey- elÕs-hair brush were considered to be alive. mashdiet (Subramanyam and Cutkomp 1987). The In the second experiment, adults of A. calandrae rice weevil, Sitophilus oryzae (L.) (Coleoptera: Cur- and T. elegans were exposed to wheat infested with culionidae), was reared on whole hard red winter S. oryzae and treated withwater or spinosad solution. wheat, and T. castaneum was reared on whole wheat Some members of the Pteromalidae require host feed- ßour plus 5% (by weight) brewerÕs yeast. The para- ing for normal oo¨genesis (Clausen 1940); thus, we sitoids Theocolax elegans (Westwood) (Hymenoptera: investigated the potential that host feeding may in- Pteromalidae) and two strains (Savannahand Bam- crease parasitoid survival in spinosad-treated wheat. berg) of Anisopteromalus calandrae (Howard) (Hy- Wheat was Þrst infested with S. oryzae and held in an menoptera: Pteromalidae), were obtained from the environmental chamber until fourth instars were USDA-ARS, Grain Marketing and Production Re- present, based on published developmental data search Center, Manhattan, KS. The Bamberg strain is (ShariÞ and Mills 1971). The wheat was then treated resistant to malathion (Baker 1994, Baker and Weaver witheitherwater or 1 mg/kg spinosad solution. 1993), whereas the Savannah strain is not. T. elegans H. hebetor was not included in this study because and A. calandrae were reared by introducing 100 adult S. oryzae is not a host for this parasitoid. In this ex- wasps (Ͻ3 d old) into 100 g of whole wheat containing periment, the Bamberg strain of A. calandrae was in- approximately 100 fourthinstars of S. oryzae. Habro- cluded to determine whether malathion resistance bracon hebetor (Say) (Hymenoptera: Braconidae) and would confer any survival beneÞts to parasitoids in a predator, the warehouse pirate bug, Xylocoris flavi- spinosad-treated wheat. Survival was assessed as de- pes (Reuter) (Heteroptera: Anthocoridae), were ob- scribed above. tained from BioFac Crop Care (Mathis, TX). H. he- X. flavipes Suppression of T. castaneum in betor was reared using the wandering stage larvae Spinosad-Treated Wheat. Because X. flavipes exhib- (Þfthinstars) of P. interpunctella, whereas X. flavipes ited signiÞcant survival in the previous experiments, was reared on T. castaneum eggs (Յ3 d old) placed in we investigated the ability of X. flavipes to suppress rolled oats. We placed 40 X. flavipes adults in 100 g of T. castaneum immatures in spinosad-treated wheat. rolled oats with Ϸ200 T. castaneum eggs, twice each Individual 0.95-liter jars containing 100 g of wheat week. All insects were reared in 0.95-liter glass jars received one of the following four treatments: distilled placed in environmental growthchambers(model water, 1 mg/kg spinosad, 1 mg/kg spinosad ϩ three I-36VL, Percival ScientiÞc, Boone, IA) maintained at female and two male X. flavipes adults, or distilled 28ЊC and 65% RH with a photoperiod of 16:8 (L:D) h. water ϩ three female and two male X. flavipes adults. All natural enemy and T. castaneum adults used in Wheat in jars was tumbled on a ball-mill roller for experiments, unless otherwise speciÞed, were Յ3 and 20 min and held at room conditions for 24 h before Յ7 d old, respectively. introduction of insects. Eachjar ( n ϭ 7 per treatment) Spinosad. SpinTor 2SC (Dow AgroSciences, India- was infested with100 T. castaneum eggs (Յ3 d old), napolis, IN) formulation containing 240 mg([AI]) spi- followed by the introduction of natural enemies. After nosad/ml was diluted in distilled water to the appro- 7 d in the growth chamber at 28ЊC and 65% RH with priate concentration for grain treatment. a photoperiod of 16:8 (L:D) h, all insects were sepa- 1176 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 97, no. 3 rated from the wheat and the number of live T. cas- the number of live T. castaneum adults and X. flavipes taneum larvae was recorded. In the second experi- adults and nymphs. Each of the four samples spanned ment, 50 Þrst and second instars of T. castaneum were from the top to the bottom of the grain mass. The four placed in separate 0.94-liter jars (n ϭ 7 per treatment) samples from eachdrum were combined and thecom- containing 100 g of wheat that received the same posite sample was sieved to separate live insects from treatments as described above. X. flavipes introduction the grain. At the termination of the test (3 mo), the occurred 4 hafter introduction of T. castaneum larvae wheat in each drum was sieved over an inclined sieve into the wheat. After 7 d, insects were separated from (White 1983) to determine the absolute numbers of the grain as described above, and the number of live live T. castaneum adults and X. flavipes adults and T. castaneum larvae was recorded. nymphs. X. flavipes nymphs were observed in the spinosad- Temperature and relative humidity of grain in a treated replications described above in which only drum were recorded 30 cm below the grain surface predator adults were introduced. Therefore, we in- near the drum center using a HOBO data logger (On- vestigated the ability of X. flavipes to reproduce in set Computer Corp., Bourne, MA). A second HOBO spinosad-treated wheat in the third test. Glass jars unit was placed on top of a drum lid to record ambient (0.95 liter), eachcontaining 400 g of wheat,were temperature and relative humidity in the room. All of treated witheitherdistilled water (control treatment, the drums were stored adjacent to each other so we n ϭ 7) or 1 mg/kg spinosad solution (treatment, n ϭ assumed conditions to be similar among drums. 7) and then infested with 10 female and 10 male Mean Ϯ SE grain temperature 30 cm below the grain T. castaneum adults. Jars were placed in the growth surface inside the drums was 19.6 Ϯ 0.4ЊC. The tem- chamber for 2 wk after which Þve female and two male perature and relative humidity of the ambient air in X. flavipes were introduced into eachjar. Jars were the room was 20.3 Ϯ 1.0ЊC and 66.4 Ϯ 5.0%, respec- examined after 8 wk, and the number of live T. cas- tively. taneum adults and X. flavipes adults and nymphs was Data Analyses. A completely random design was counted. used for all tests. Survival of natural enemies was In the fourth experiment, the ability of X. flavipes to adjusted for mortality in the control treatments by suppress T. castaneum populations over a 3-mo period using the method of Abbott (1925). The response was evaluated in 208-liter plastic drums, eachholding variables were the proportion of the sample popula- 163.3 kg of wheat. Wheat for this study could not be tion that survived in the laboratory (jar) experiments frozen due to practical constraints on freezer space. and actual number of live insects recovered in the Two unbaited probe traps (Storgard WB-II, Tre´ce´ drum study. Before statistical procedures, proportions Inc., Salinas, CA), inserted into the wheat bulk for 48 h were transformed using arcsine square root, whereas before grain treatment, did not capture any live in- the number of live insects was transformed to loga- sects. This indicated that the wheat was relatively rithmic scale (Zar 1984). Statistical inferences were insect-free before use in our experiments. The wheat made after subjecting data to PROC MIXED (SAS in eachdrum ( n ϭ 3 per treatment) was treated with Institute 1999), withdegree of freedom adjustments distilled water, water ϩ X. flavipes, spinosad at 1 mg/ for the variance components following the methods of kg, or spinosad at 1 mg/kg ϩ X. flavipes. Wheat was Satterthwaite (1946). The analysis of variance preweighed and then moved into an overhead bin (ANOVA) for repeated measures was used for ana- with a pneumatic conveyor where a gate regulated the lyzing drum data as the same experimental units ßow out of the overhead bin. Distilled water or aque- (drums) were sampled monthly. Treatment means ous spinosad suspension was applied to the falling were separated using pairwise comparisons of least grain stream (0.7 ml/kg of grain) witha sprayer squares means (LSMEANS) at the ␣ ϭ 0.05 level. (model 1126, Cummins Industrial Tools, Spring Hill, Untransformed means and standard errors are pre- KS) powered by compressed air at 103.4-kPa pressure. sented in tables and Þgures. From the overhead bin, wheat fell 1 m into a grain hopper that fed the wheat into a 4.9-m-long electric Results grain auger (10.2 cm diameter), positioned 30Њ from horizontal that dropped the grain into the plastic Spinosad Toxicity to Natural Enemies. On un- drums. treated wheat (control), the survival (mean Ϯ SE) of Forty unsexed adults of T. castaneum (Յ2 wk old) natural enemies was 72.2 Ϯ 2.8% for T. elegans, 87.6 Ϯ were introduced into eachdrum 5 d after grain treat- 2.7% for X. flavipes, 90.7 Ϯ 2.4% for A. calandrae, and ment. Three weeks after T. castaneum introduction, 71.0 Ϯ 4.8% for H. hebetor. Survival of these natural Þve female and Þve male X. flavipes adults (Յ1 wk old) enemies in spinosad-treated wheat, adjusted for mor- were released into eachof theappropriate treatment tality in the control treatments, is shown in Fig. 1. drums. Plastic drums were then individually sealed X. flavipes was the only species that had Ͼ90% survival and stored in the research ßour mill located in the in wheat treated with 1 mg/kg spinosad. All hyme- third ßoor of the Department of Grain Science and nopteran species experienced Ͻ30% survival in wheat Industry, Kansas State University. treated with0.1 mg/kg spinosad, and none survived in Four separate grain samples (Ϸ350 g per sample) wheat treated with 1 mg/kg spinosad. were taken monthlyfrom eachdrum witha 1.2-m-long The presence of hosts did not affect the survival of grain trier (Seedburo Equipment Co.) to determine A. calandrae and T. elegans in the control and spinosad- June 2004 TOEWS AND SUBRAMANYAM:SUSCEPTIBILITY OF NATURAL ENEMIES TO SPINOSAD 1177

Fig. 3. Mean Ϯ SE proportion of live T. castaneum larvae Fig. 1. Mean Ϯ SE proportion of natural enemies sur- recovered after7dinjars of wheat initially infested with 50 viving 24-h exposure to spinosad-treated wheat (no hosts Þrst and second instars. Means followed by different letters present). Data were adjusted for mortality in the control are signiÞcantly different (P Ͻ 0.05; LSMEANS test). replicates. In the 8-wk study, we observed signiÞcant survival of T. castaneum adults and survival and reproduction treated wheat. Survival in the control treatments with of X. flavipes (Fig. 4). The mean number of T. casta- hosts present was 79.2 Ϯ 11.6 and 87.6 Ϯ 2.2% for the neum adults recovered at the end of the study was Bamberg and Savannahstrains of A. calandrae, respec- Ϯ similar between the control and spinosad treatments tively, and 75.6 6.0% for T. elegans. The survival of (F ϭ 0.41; df ϭ 11, 1; P ϭ 0.534). Likewise, the number these species in wheat treated with 1 mg/kg spinosad ϭ ϭ ϭ Ͻ of X. flavipes adults (F 1.88; df 1, 11; P 0.197) was 2%. and nymphs (F ϭ 4.07; df ϭ 1, 11; P ϭ 0.069) recovered X. flavipes Suppression of T. castaneum in Spinosad- also was similar between these two treatments. The Treated Wheat. In the test with T. castaneum eggs, presence of X. flavipes nymphs clearly indicates adult many more T. castaneum larvae were recovered in the reproduction and nymphal survival on spinosad- control treatment than in the other treatments (Fig. treated wheat, but it is not clear whether the adult 2). Spinosad treatment alone decreased T. castaneum insects recovered from the experiment represent sur- larval survival by 90%, whereas no larvae were recov- ϩ vivors of the initial cohort (introduced insects) or ered in the X. flavipes and spinosad X. flavipes progeny that matured to adulthood. treatments. Similar results were observed in experi- Overall repeated measures ANOVA showed that ments starting with T. castaneum Þrst and second in- there were signiÞcant differences among treatments stars (Fig. 3). There was an 88% decrease in T. casta- in the number of live T. castaneum adults recovered neum larval numbers in spinosad and X. flavipes only from the grain trier samples (F ϭ 44.6; df ϭ 3, 8; P ϭ treatments relative to the control treatment. No 0.001). The control treatment had 7.6 Ϯ 2.1 T. casta- T. castaneum larvae were recovered from the combi- neum adults per kilogram of grain, which was statis- nation treatment.

Fig. 4. Mean Ϯ SE number of T. castaneum adults, X. flavipes adults, and X. flavipes nymphs recovered after 8 wk Fig. 2. Mean Ϯ SE proportion of live T. castaneum larvae in jars of T. castaneum-infested wheat treated with aliquots of recovered after7dinjars of wheat initially infested with 100 distilled water (control treatment) or spinosad at 1 mg/kg. eggs. Means followed by different letters are signiÞcantly Treatment means within species and life stage are not sig- different (P Ͻ 0.05; LSMEANS test). niÞcantly different from one another (see text for details). 1178 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 97, no. 3

Table 1. Number (mean ؎ SE) of live T. castaneum adults, X. flavipes adults, and X. flavipes nymphs per kilogram of wheat obtained using a grain trier during the 3-mo drum test

Treatment Insect and life stage Month Control X. flavipes Spinosad Spinosad ϩ X. flavipes T. castaneum adults 1 3.3 Ϯ 0.6a 2.8 Ϯ 0.1a 0.0 Ϯ 0.0b 0.0 Ϯ 0.0b 2 8.3 Ϯ 2.5a 2.4 Ϯ 0.9b 0.3 Ϯ 0.3c 0.0 Ϯ 0.0c 3 11.3 Ϯ 5.2a 2.4 Ϯ 1.0b 0.0 Ϯ 0.0c 0.0 Ϯ 0.0c X. flavipes adults 1 Ña 1.4 Ϯ 1.1a Ñ 0.0 Ϯ 0.0a 2 Ñ 0.3 Ϯ 0.3a Ñ 0.0 Ϯ 0.0a 3 Ñ 0.5 Ϯ 0.3a Ñ 0.0 Ϯ 0.0a X. flavipes nymphs 1 Ñ 0.2 Ϯ 0.2a Ñ 0.0 Ϯ 0.0a 2 Ñ 1.0 Ϯ 0.7a Ñ 0.0 Ϯ 0.0a 3 Ñ 0.5 Ϯ 0.3a Ñ 0.0 Ϯ 0.0a

Means within a row (month) followed by different letters are signiÞcantly different (P Ͻ 0.05; LSMEANS test). a Not applicable. tically different (P Ͻ 0.05) from the X. flavipes treat- the organophosphates (Salgado 1998, Sparks et al. ment (2.6 Ϯ 0.4) (Table 1). The spinosad (0.1 Ϯ 0.1) 2001). Survivorship of hymenopteran species in the and the spinosad ϩ X. flavipes treatments (0.0 Ϯ 0.0) control (distilled water) treatments was not 100%, were statistically similar (P Ͼ 0.05). probably because of the sieving process, in which Absolute densities derived from sieving all of the delicate parasitoid species may have suffered addi- grain at the end of the study (Table 2) showed dif- tional mortality. X. flavipes is a more stout-bodied ferences among treatments in the number of T. cas- insect, and was perhaps, less affected by the sieving. A taneum adults (F ϭ 29.26; df ϭ 3, 8; P ϭ 0.001) or general lack of survival among hymenopterans ex- X. flavipes adults (F ϭ 12.73; df ϭ 1, 4; P ϭ 0.023), but posed to spinosad was also reported in the literature not X. flavipes nymphs (F ϭ 2.92; df ϭ 1, 4; P ϭ 0.163). (Tillman and Mulrooney 2000, Mason et al. 2002, Contamination by 105 live sawtoothed grain beetles, Michaud 2003). Oryzaephilus surinamensis (L.) (Coleoptera: Silvani- There is limited evidence to suggest that X. flavipes dae), was observed while sifting one drum of the is more pesticide-tolerant than parasitoids and pest X. flavipes treatment. Although exclusion of this rep- insects. Baker and Arbogast (1995) reported X. flavi- licate from the data set decreased the mean T. casta- pes to be 4- and 10-fold more tolerant to malathion neum population in the X. flavipes treatment from than A. calandrae and H. hebetor, respectively. Press et 67.0 Ϯ 52.7 to 14.5 Ϯ 7.5 adults per drum, the number al. (1978) reported that X. flavipes generally exhibited of T. castaneum adults present was still greater than greater tolerance to the insecticides permethrin, fe- that observed in the spinosad or spinosad ϩ X. flavipes nitrothion, pirimiphos-methyl, pyrethrins ϩ piperonyl treatments (Table 2). butoxide, and malathion than three prey species, in- cluding T. castaneum; the cigarette beetle, Lasioderma serricorne (F.); and P. interpunctella. Tillman and Mul- Discussion rooney (2000) found that counts of a hemipteran Our results indicate that spinosad treatment of hard predator Geocoris punctipes (Say) (Hemiptera: Lyg- red winter wheat at 1 mg/kg greatly decreased the aidae), were not affected by spinosad in cotton Þelds. survival of all the hymenopteran parasitoids, but not The exact mechanism by which X. flavipes is able to that of the predator X. flavipes. A similar lack of sur- metabolize or tolerate moderately high doses of pes- vival of the parasitoid species in tests with and without ticides, including spinosad, is unknown and warrants hosts leads us to believe that spinosad poisoning ad- further study. versely affected the parasitoids. The Savannah and Suppression of T. castaneum in spinosad-treated Bamberg strains of A. calandrae were equally suscep- wheat was variable. In experiments with T. castaneum tible to spinosad, suggesting that malathion resistance eggs and small larvae, very few larvae were recov- in the Bamberg strain did not confer cross-resistance ered after 7 d, which indicated high susceptibility of to spinosad. This result is not surprising, because spi- T. castaneum larvae to spinosad. In the 8-wk experi- nosad has a completely different mode of action than ments, we recovered nearly one-half of the introduced

Table 2. Number (mean ؎ SE) of live T. castaneum adults, X. flavipes adults, and X. flavipes nymphs recovered after sieving all of the grain in drums after 3 mo

Treatment Insect and life stage Control X. flavipes Spinosad Spinosad ϩ X. flavipes T. castaneum adults 396.0 Ϯ 50.0a 67.0 Ϯ 52.7b 1.0 Ϯ 0.6c 0.3 Ϯ 0.3c X. flavipes adults 14.0 Ϯ 9.5a 0.0 Ϯ 0.0b X. flavipes nymphs 21.0 Ϯ 18.1a 0.0 Ϯ 0.0a

Means within a row followed by different letters are signiÞcantly different (P Ͻ 0.05; LSMEANS test). June 2004 TOEWS AND SUBRAMANYAM:SUSCEPTIBILITY OF NATURAL ENEMIES TO SPINOSAD 1179 adult population. In the drum study, only one adult Baker, J. E., and D. K. Weaver. 1993. Resistance in Þeld was recovered in spinosad-treated wheat at the end of strains of the parasitoid Anisopteromalus calandrae (Hy- the 3-mo test. There is substantial evidence to show menoptera: Pteromalidae) and its host, Sitophilus oryzae that spinosad at 1 mg/kg is not effective in killing all (Coleoptera: Curculionidae), to malathion, chlorpyrifos- exposed adults, but this rate is effective in suppressing methyl, and pirimiphos-methyl. Biol. Control 3: 233Ð242. progeny of T. castaneum (Fang et al. 2002a,b), thereby Boucher, J. 1999. Effect of spinosad on bell peppers pests limiting any population growthto contamination from and beneÞcial arthropods, 1998. Manage. Tests 24: 144. external sources or other forms of immigration. Bret, B. L., L. L. Larson, J. R. Schoonover, T. C. Sparks, and Contamination by O. surinamensis in one replica- G. D. Thompson. 1997. Biological properties of spi- tion of X. flavipes treated grain in the drum study likely nosad. Down to Earth52: 6Ð13. decreased the observed suppression of T. castaneum. Clausen, C. P. 1940. Entomophagous insects. Hafner Pub- O. surinamensis attacks nearly all cereal grains and has lishing Co., Inc., New York. a reproductive potential of 6Ð10 eggs per female per Fang, L., Bh. Subramanyam, and F. H. Arthur. 2002a. Ef- day (Howe 1956). Because O. surinamensis is a known fectiveness of spinosad on four classes of wheat against prey of X. flavipes (Arbogast 1976), the reduced sup- Þve stored-product insects. J. Econ. Entomol. 95: 640Ð pression of T. castaneum was likely due to X. flavipes 650. feeding on the sizable O. surinamensis population in Fang, L., Bh. Subramanyam, and S. Dolder. 2002b. Fate addition to the T. castaneum population. The exact and efÞcacy of spinosad residues in farm-stored wheat. time and source of the contamination remains un- J. Econ. Entomol. 95: 1102Ð1109. GIPSA. 1997. Grain inspection handbook, book II, wheat. known, but it could have resulted from immigration http://ww.usda.gov/gipsa/reference-library/handbooks/ during the 4-wk window between fumigation of the grain-insp/grbook2/gihbk2.htm. grain and drum-Þlling. Howe, R. W. 1956. The biology of the two common storage Our results indicate that X. flavipes can survive, species of Oryzaephilus (Coleoptera, Cucujidae). Ann. reproduce, and suppress T. castaneum populations in Appl. Biol. 44: 341Ð355. wheat treated with Յ1 mg/kg spinosad, whereas the Mason, P. G., M. A. Erlandson, R. H. Elliott, and B. J. Harris. parasitoids were highly susceptible to spinosad poi- 2002. Potential impact of spinosad on parasitoids of soning. T. castaneum suppression withspinosad at Mamestra configurata (Lepidoptera: Noctuidae). Can. 1 mg/kg alone was generally equal to or greater than Entomol. 134: 59Ð68. the suppression achieved with X. flavipes. This Þnding Michaud, J. P. 2003. Toxicity of fruit ßy baits to beneÞcial leads us to believe there may be limited beneÞts in insects in citrus. J. Insect Sci. 3:8, available online: combining spinosad with X. flavipes for T. castaneum insectscience.org/3.8. Press, J. W., B. R. Flaherty, and L. L. McDonald. 1978. suppression in the storage situations tested. Toxicity of Þve insecticides to the predaceous bug Xylo- coris flavipes (Hemiptera: Anthocoridae). J. Ga. Entomol. Soc. 13: 177Ð181. Acknowledgments Salgado, V. L. 1998. Studies on the mode of action of spi- nosad: insect symptoms and physiological correlates. We thank Jackie Rowan, Zeb Larson, and Glen Swartz for Pestic. Biochem. Physiol. 60: 91Ð102. technical assistance. 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