Chlorethoxyfos

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.

Abstract: Background The western corn rootworm is an economically important pest of corn. Management tactics include pyrethroid and organophosphate insecticides, which may be applied as a mixture to protect corn roots. The goal of our study was to characterize the effects of pyrethroids and organophosphates alone and in combination on larval corn rootworm mortality and injury to corn roots. We evaluated two insecticide combinations: tebupirimphos with β-cyfluthrin and chlorethoxyfos with bifenthrin. Using a soil-based, laboratory bioassay, we exposed larvae to five concentrations of the pyrethroid alone, the organophosphate alone, the combined formulation, and a water control. We calculated LC50 values and co-toxicity factors to determine synergism or antagonism between organophosphates and pyrethroids. We also measured adult emergence and root injury in a field experiment that tested tebupirimphos alone, β-cyfluthrin alone, the combined formulation, and an untreated control. Results Bioassay results indicated antagonism between the pyrethroid and organophosphate at most concentrations for both insecticide combinations. In the field experiment, tebupirimphos alone or in combination with β-cyfluthrin significantly reduced adult emergence and root injury compared to the untreated controls, but β-cyfluthrin alone did not differ from the untreated control for either metric. Conclusions These results suggest that, at the concentrations tested, the pyrethroid component of pyrethroid-organophosphate mixtures may not contribute to a reduction of rootworm emergence or root injury. While these pyrethroids may confer a management benefit for other pests, such as seedcorn maggot, the concentrations of pyrethroids present in current formulations of these mixtures are likely too low for effective rootworm management. © 2020 Society of Chemical Industry.