Imidacloprid-induced hormesis effects on demographic traits of the melon aphid, Aphis gossypii

Imidacloprid is a largely commercialized neonicotinoid insecticide, and it is used effectively against a variety of sap-sucking insect pests including melon aphid, Aphis gossypii. In this study, the inhibitory and stimulatory effects of low and sublethal concentrations of imidacloprid were investigated on two successive generations of A. gossypii. The initial bioassay results showed that imidacloprid exhibited high toxicity against adult melon aphids with a LC50 of 0.42 mg/l after 72 h exposure. The low lethal (LC15) and sublethal (LC5) concentrations of imidacloprid reduced adult longevity and fecundity in exposed aphids (F-0). By contrast, hormesis effects were observed on the biological traits of progeny generation (F-1) exposed to both concentrations of imidacloprid. Substantial increases were noted for the adult longevity and fecundity of F-1 aphids. Consequently, the demographic indexes such as intrinsic rate of increase (r) and finite rate of increase (lambda) were enhanced by both concentrations whereas the net reproductive rate (R-0) and gross reproduction rate (GRR) were increased only by the LC15 of imidacloprid. Nonetheless, the mean generation time (T) of F-1 A. gossypii was extended by the LC5 and LC15 of imidacloprid. These results indicated that low or sublethal concentrations of imidacloprid, while negatively affecting biological traits of directly exposed aphids, could induce hormesis effects in the progeny of exposed individuals in the aphid A. gossypii. Therefore, the occurrence of potential hormesis should be taken into consideration when using imidacloprid against aphid pests.