Fecundity and Egg Viability of Northern and Western Corn Rootworm (Coleoptera: Chrysomelidae) Beetles Surviving Labeled and Reduced Soil Insecticide Applications

Abstract

The influence of soil insecticide application rates on the reproductive biologies of field-collected northern and western corn rootworms, Diabrotica barberi Smith & Lawrence, and D. virgifera virgifera LeConte, respectively, was investigated under laboratory conditions. Comparisons were made on beetles obtained from plots treated with planting-time applications of labeled (IX) and reduced (0.5 and 0.75X) rates of chlorethoxyfos, tefluthrin, and terbufos, and from untreated control plots. Captured insects were pooled by species and insecticide treatment into laboratory rearing cages and allowed to mate. Gravid females were held individually in oviposition chambers to assess fecundity. Egg viability was measured on subsamples of eggs from all treatments. No significant differences ( P >0.05) were detected in fecundity, fertility, or percentage of nonviable eggs of D. barberi or D. virgifera with any insecticide or application rate within insecticide tested. However, reductions in total eggs produced and hatch were 31.2 and 53.7%, respectively, for D. virgifera that survived chlorethoxyfos treatment in comparison with beetles that emerged from untreated plots. Also, the percentage of nonviable eggs produced by D. virgifera emerging from chlorethoxyfos-treated plots was 2-fold of that in beetles captured from untreated corn plots. Whereas, D. barberi females from tefluthrin-treated plots experienced a 44% increase in fecundity and 49.2% more egg hatch than those from the untreated controls. Additionally, total eggs and hatch were increased by 32.1 and 33.7%, respectively, in D. barberi that emerged from terbufos-treated corn plots when compared with their counterparts from untreated control plots. The numerical disparities that we observed appeared to be species specific rather than associated with insecticide class or application rate. Our evaluations indicate that using reduced (0.5 and O.75X) application rates of these organophosphate and pyrethroid insecticides will not likely have major effects on the reproductive capacities of D. barberi or D. virgifera . Thus, corn rootworm management programs should include options for using the lowest efficacious application rates of these insecticides.