Bhadriraju Subramanyam

Alternatives to pesticides in stored-product IPM

Dedication. Contributors. About the editors. Preface. 1. Monitoring and decision tools D.W. Hagstrum, B. Subramanyam. 2. Sanitation and exclusion M.A. Mullen, J.R. Pederson. 3. Aeration C. Reed, F.H. Arthur. 4. Temperature C.S. Burks, et al. 5. Modified atmospheres C. Adler, et al. 6. Insect growth regulators H. Oberlander, D.L. Silhacek. 7. Varietal resistance J.E. Throne, et al. 8. Pathogens D. Moore, et al. 9. Parasites and predators M. Scholler, P.W. Flinn. 10. Pheromones T.W. Phillips, et al. 11. Botanicals D.K. Weaver, B. Subramanyam. 12. Inert dusts B. Subramanyam, R. Roesli. 13. Radiation S.L. Halverson, S.V. Nablo. 14. Impact R. Plarre, F. Reichmuth. 15. Integration D.W. Hagstrum, B. Subramanyam. Index.

Effectiveness of Spinosad on Four Classes of Wheat Against Five Stored-Product Insects

Abstract Spinosad is a commercial reduced-risk pesticide that is naturally derived. Spinosad’s performance was evaluated on four classes of wheat (hard red winter, hard red spring, soft red winter, and durum wheats) against adults of the lesser grain borer, Rhyzopertha dominica (F.); rice weevil, Sitophilus oryzae (L.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); red flour beetle, Tribolium castaneum (Herbst); and larvae of the Indianmeal moth, Plodia interpunctella (Hübner). Beetle adults (25) or P. interpunctella eggs (50) were exposed to untreated wheat and wheat treated with spinosad at 0.1 and 1 mg (AI)/kg of grain. On all untreated wheat classes, adult beetle mortality ranged from 0 to 6%, and P. interpunctella larval mortality ranged from 10 to 19%. The effects of spinosad on R. dominica and P. interpunctella were consistent across all wheat classes. Spinosad killed all exposed R. dominica adults and significantly suppressed progeny production (84–100%) and kernel damage (66–100%) at both rates compared with untreated wheat. Spinosad was extremely effective against P. interpunctella on all wheat classes at 1 mg/kg, based on larval mortality (97.6–99.6%), suppression of egg-to-adult emergence (93–100%), and kernel damage (95–100%), relative to similar effects on untreated wheats. The effects of spinosad on S. oryzae varied among wheat classes and between spinosad rates. Spinosad was effective against S. oryzae, O. surinamensis and T. castaneum only on durum wheat at 1 mg/kg. Our results suggest spinosad to be a potential grain protectant for R. dominica and P. interpunctella management in stored wheat.

Time-Mortality Relationships for Tribolium castaneum (Coleoptera: Tenebrionidae) Life Stages Exposed to Elevated Temperatures

The use of elevated temperatures (> or = 40-60 degrees C) or heat treatments for managing insects in food-processing facilities is a viable alternative to space fumigation with methyl bromide. Quantitative data are lacking on the responses of life stages of the red flour beetle, Tribolium castaneum (Herbst), an important pest of food-processing facilities worldwide, to elevated temperatures used during heat treatments. We determined time-mortality relationships for eggs, young (neonate) larvae, old larvae, pupae, and adults of T. castaneum, exposed to constant temperatures of 42, 46, 50, 54, 58, and 60 degrees C. Generally, mortality of each stage increased with an increase in temperature and exposure time. Young larvae were the most heat-tolerant stage, especially at temperatures > or = 50 degrees C. Exposure for a minimum of 7.2 h at > or = 50 degrees C was required to kill 99% of young larvae, whereas the other stages required < or = 1.8 h. Heat treatments that control young larvae should control all other stages of T. castaneum, and young larvae should be used as test insects to evaluate efficacy against T. castaneum during an actual facility heat treatment. These results provide the basis for successful use of elevated temperatures for management of T. castaneum life stages associated with food-processing facilities.

Changes in Expression of Heat Shock Proteins in Tribolium castaneum (Coleoptera: Tenebrionidae) in Relation to Developmental Stage, Exposure Time, and Temperature

Abstract The use of elevated temperatures or heat treatments for managing insect pests in food-processing facilities is becoming a popular alternative to methyl bromide fumigation. We found that young larvae (first instars) of red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), were relatively more tolerant to elevated temperatures than eggs, old larvae, pupae, and adults. Our objective was to determine whether heat shock proteins (HSPs) confer thermotolerance in T. castaneum life stages. Western blot analyses by using HSP 70 antibody showed constitutive expression of HSP 70 in all stages of T. castaneum. However, the expression of HSP 70 in young larvae increased by ≈33%, after the larvae were exposed to 40°C for 1 h. The expression of HSP 70 in other stages did not vary significantly, but for eggs the expression of HSP 70 showed significant reduction at 40°C. Young larvae possessed two distinct HSPs with molecular masses of 70 and 24 kDa, both recognized by a monoclonal anti-bovine brain HSP 70 antibody. Our study suggests that increased thermotolerance in young larvae could be due to increased expression of HSP 70 at higher temperatures. Time- and temperature-dependent expression of HSP 70 showed that the increased thermotolerance in young larvae might last as long as 8 h at 40°C or 30 min at 46°C.

Effects of delayed mating on reproductive performance of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Virgin male and female Indianmeal moths, Plodia interpunctella (H . ubner), were mated soon after emergence or delayed from mating for 1–5 d, to determine the effect of age at mating on the number of spermatophores transferred by males to females, number of eggs laid (fecundity), egg viability, and adult longevity. When male and female moths were mated without delay, all females mated successfully. On average, each mated female had 2.2 spermatophores and laid 161 eggs. About 99% of the eggs laid were viable. Fecundity and egg viability were significantly and positively correlated with the number of spermatophores/female. For each day that mating of virgin male or female P. interpunctella was delayed, fecundity decreased by about 25 eggs. Egg viability decreased by 22%/d only when females were delayed from mating. Males delayed from mating for 5 d were unable to inseminate females. However, about 23% of females had one spermatophore when females or both males and females were delayed from mating for 5 d. On average, 22–39 non-viable eggs were laid by a female in treatments where male or female moths were delayed from mating for 5 d. Similarly, unmated (virgin) females laid 33 non-viable eggs. These results suggest that methods that can delay and disrupt mating may be effective behavioral strategies for managing this important pest of stored commodities and processed foods. r 2002 Elsevier Science Ltd. All rights reserved.

Effectiveness of spinosad against seven major stored-grain insects on corn

Abstract In January 2005, the United States Environmental Protection Agency registered spinosad as a stored grain protectant. No referenced data on the efficacy of spinosad on corn in suppressing major stored‐grain insects have been published. In this paper, we evaluated the efficacy of spinosad against seven major stored‐grain insects on shelled corn in the laboratory. Insect species tested were the red flour beetle, Tribolium castaneum (Jacquelin duVal); rusty grain beetle, Cryptolestesferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); rice weevil, Sitophilus oryzae (L.); maize weevil, Sitophilus zeamais (Motschulsky); and Indian meal moth, Plodia interpunctella (Hübner). Corn kernels were treated with spinosad at 0, 0.1, 0.5, 1, and 2 active ingredient (a.i.) mg/kg for controlling the seven species. Beetle adults or P. interpunctella eggs were introduced into each container holding 100 g of untreated or insecticide‐treated corn. The seven insect species survived well on the control treatment, produced 28 to 336 progeny, and caused significant kernel damage after 49 days. On spinosad‐treated corn, adult mortality of C. ferrugineus, R. dominica, O. surinamensis, S. oryzae, and S. zeamais was > 98% at 1 and 2 mg/kg after 12 days. Spinosad at > 0.5 mg/kg completely suppressed egg‐to‐larval survival after 21 days and egg‐to‐adult emergence of P. interpunctella after 49 days, whereas 16%T. castaneum adults survived at 1 mg/kg after 12 days. Spinosad at 1 or 2 mg/kg provided complete or near complete suppression of progeny production and kernel damage of all species after 49 days. Our results indicate that spinosad at the current labeled rate of 1 mg/kg is effective against the seven stored‐grain insect pests on corn.

Immediate and Delayed Mortality of Rhyzopertha dominica (Coleoptera: Bostrichidae) and Sitophilus oryzae (Coleoptera: Curculionidae) Adults Exposed to Spinosad-Treated Commodities

Abstract A series of tests was conducted to characterize differences in the mortality of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), exposed to three commodities treated with a liquid and dry spinosad formulation. In laboratory bioassays, adults of the two insect species were exposed to untreated wheat, Triticum aestivum L., corn, Zea mays L., and sorghum, Sorghum bicolor (L.) Moench., and to commodities treated with 1 mg (AI)/kg of liquid and dry spinosad formulations. Mortality was assessed from independent samples examined at specific time intervals to determine immediate mortality and after 24 h of recovery on untreated grain at 28°C and 65% RH to determine delayed mortality. Comparison of the time required for 50% (LT50) and 95% (LT95) mortality indicated that R. dominica adults were consistently and significantly more susceptible (died quickly) than S. oryzae adults when exposed to spinosad-treated commodities. In general, the toxicity of liquid and dry spinosad formulations was similar against R. dominica or S. oryzae. The toxicity of spinosad to each species varied slightly among the three commodities, and there were no consistent trends to suggest that spinosad was more effective on one commodity versus another. LT50 values based on immediate mortality for R. dominica on all commodities ranged from 0.45 to 0.74 d; corresponding values based on delayed mortality ranged from 0.04 to 0.23 d, suggesting delayed toxic action of spinosad in R. dominica. LT50 values based on immediate and delayed mortality for S. oryzae on all three commodities treated with the two spinosad formulations were essentially similar and ranged from 2.75 to 4.56 d. LT95 values for R. dominica based on immediate mortality on spinosad-treated commodities ranged from 1.75 to 3.36 d, and those based on delayed mortality ranged from 0.49 to 1.88 d. There were no significant differences in LT95 values based on immediate and delayed mortality for S. oryzae on spinosad-treated commodities, and the LT95 values ranged from 7.62 to 18.87 d. The toxicity of spinosad was enhanced during a 24-h holding period after removal from spinosad-treated commodities only against R. dominica adults, and possible reasons for increased postexposure mortality of R. dominica adults after brief exposures to spinosad warrant further study.

Diagnostic Molecular Markers for Phosphine Resistance in U.S. Populations of Tribolium castaneum and Rhyzopertha dominica

Stored product beetles that are resistant to the fumigant pesticide phosphine (hydrogen phosphide) gas have been reported for more than 40 years in many places worldwide. Traditionally, determination of phosphine resistance in stored product beetles is based on a discriminating dose bioassay that can take up to two weeks to evaluate. We developed a diagnostic cleaved amplified polymorphic sequence method, CAPS, to detect individuals with alleles for strong resistance to phosphine in populations of the red flour beetle, Tribolium castaneum, and the lesser grain borer, Rhyzopertha dominica, according to a single nucleotide mutation in the dihydrolipoamide dehydrogenase (DLD) gene. We initially isolated and sequenced the DLD genes from susceptible and strongly resistant populations of both species. The corresponding amino acid sequences were then deduced. A single amino acid mutation in DLD in populations of T. castaneum and R. dominica with strong resistance was identified as P45S in T. castaneum and P49S in R. dominica, both collected from northern Oklahoma, USA. PCR products containing these mutations were digested by the restriction enzymes MboI and BstNI, which revealed presence or absence, respectively of the resistant (R) allele and allowed inference of genotypes with that allele. Seven populations of T. castaneum from Kansas were subjected to discriminating dose bioassays for the weak and strong resistance phenotypes. Application of CAPS to these seven populations confirmed the R allele was in high frequency in the strongly resistant populations, and was absent or at a lower frequency in populations with weak resistance, which suggests that these populations with a low frequency of the R allele have the potential for selection of the strong resistance phenotype. CAPS markers for strong phosphine resistance will help to detect and confirm resistant beetles and can facilitate resistance management actions against a given pest population.

Methodology for assessing rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica

Abstract Several physical and chemical attributes of rice were evaluated to determine which character would be best to use to assess multiple rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica (F.). Laboratory tests were conducted on single varieties of long-, short-, and medium grain-rice to develop procedures and methodologies that could be used for large-scale screening studies. Progeny production of R. dominica was positively correlated with the percentage of broken hulls. Although kernel hardness, amylose content, neonate preference for brown rice, and adult emergence from neonates varied among the three rice varieties tested they did not appear to be valid indicators of eventual progeny production, and may not be useful predictors of resistance or susceptibility. Soundness and integrity seem to be the best characters to use for varietal screening studies with R. dominica.

Dynamic Model for Predicting Survival of Mature Larvae of Tribolium confusum During Facility Heat Treatments

Abstract Structural heat treatment, a viable alternative to methyl bromide fumigation, involves raising the ambient temperature of food-processing facilities between 50 and 60°C by using gas, electric, or steam heaters, and holding these elevated temperatures for 24 h or longer to kill stored-product insects. A dynamic model was developed to predict survival of mature larvae, which is the most heat-tolerant stage of the confused flour beetle, Tribolium confusum (Jacquelin du Val), at elevated temperatures between 46 and 60°C. The model is based on two nonlinear relationships: 1) logarithmic survival of T. confusum mature larvae as a function of time, and 2) logarithmic reduction in larval survival as a function of temperature. The dynamic model was validated with nine independent data sets collected during actual facility heat treatments conducted on two separate occasions at the Kansas State University pilot flour and feed mills. The rate of increase of temperature over time varied among the nine locations where mature larvae of T. confusum were exposed, and the approximate heating rates during the entire heat treatment ranged from 1.1 to 13.2°C/h. The absolute deviation in the predicted number of larvae surviving the heat treatment was within 3–7% of the actual observed data. Comparison of the absolute deviation in the time taken for equivalent larval survival showed that the model predictions were within 2–6% of the observed data. The dynamic model can be used to predict survival of mature larvae of T. confusum during heat treatments of food-processing facilities based on time-dependent temperature profiles obtained at any given location.