Sublethal and transgenerational effects of lambda-cyhalothrin on the mirid bugs Lygus pratensis Linnaeus and Polymerus cognatus Fieber

The plant mirid bugs, Lygus pratensis Linnaeus and Polymerus cognatus Fieber, are key pests on economically important cotton crops and ecologically important grassland in northwestern China. Lambda-cyhalothrin is frequently used against mirid bugs in the regions. In this study, we examined the sublethal and transgenerational effects of short-term exposure to lambda-cyhalothrin on biological traits using a miminal dose, LD5 [0.484 ng/L. pratensis adult, and 0.171 ng/P. cognatus adult], a low lethal dose, LD25 [1.353 ng/L. pratensis adult, and 0.781ng/P. cognatus adult] and a moderate lethal dose, LD50 [2.766 ng/L. pratensis adult, and 2.243 ng/P. cognatus adult]. Direct exposure to LD50 of lambda-cyhalothrin led to decreased adult longevity, shorter female oviposition period and lower fecundity of the parental generation for both species, whereas treatment with LD5 lambda-cyhalothrin stimulated female fecundity on L. pratensis, but not on P. cognatus. The F1 generation underwent transgenerational effects, i.e. there was delayed egg-laying period and larval development and decreased hatchability for both species, decreased adult longevity and fecundity for L. pratensis, and shortened adult longevity for the LD50 group of P. cognatus. Compared with the untreated control group, the net reproductive rate (R0), the intrinsic rate of increase (rm), and finite rate of increase (λ) were significantly decreased for the groups treated with different doses of lambda-cyhalothrin, whereas the generation time (T) was increased. Our results demonstrate that sublethal effects of lambda-cyhalothrin can retard development and suppress population growth for both of these mirid species. Therefore, this insecticide can be used effectively against mirid
bugs in northern China and its application strategy to control mirid bug is discussed.