Effects of exposure to imidacloprid direct and poisoned cotton aphids Aphis gossypii on ladybird Hippodamia variegata feeding behavior

Imidacloprid is a pesticide used to control aphid infestations of cotton plants. However, poisoned aphids also serve as food for the ladybird natural predator Hippodamia variegata. We investigated whether imidacloprid-treated eggs, pupae, and adults of H. variegata and poisoned aphids altered ladybird predatory behavior. Laboratory bioassay results demonstrated that 0.72 g/L imidacloprid was lethal to ladybirds. Imidacloprid significantly reduced the hatching and emergence rates of H. variegata, and these effects were time and dose dependent. Predation was most adversely affected when the ladybirds directly consumed poisoned aphids and less so when directly exposed to the insecticide at sublethal concentrations. Imidacloprid use in cotton fields should be restricted to the initial stages of aphid infestation to avoid the period when adult ladybirds are present.