Does the dose make the poison? Neurotoxic insecticides impair predator orientation and reproduction even at low concentrations

Abstract

BACKGROUND: Pesticides can be noxious to non-target beneficial arthropods and their negative effects have been recently rec-ognized even at low doses. The predatorNesidiocoris tenuis(Reuter) (Hemiptera: Miridae) plays an important role in controllinginsect pests in solanaceous crops, but its concurrent herbivory often poses relevant concerns for tomato production. Althoughinsecticide side effects onN. tenuishave been previously studied, little is known on the potential implications of neurotoxic che-micals at low concentrations. We assessed the baseline toxicity of three neurotoxic insecticides (lambda-cyhalothrin, spinosadand chlorpyrifos) onN. tenuisby topical contact exposure. The behavioral and reproduction capacity of the predator was theninvestigated upon exposure to three estimated low-lethal concentrations (LC1,LC10and LC30).RESULTS: Predator survival varied among insecticides and concentrations, with LC30/label rate ratios ranging from 8.45% to65.40% for spinosad and lambda-cyhalothrin, respectively. All insecticides reduced the fertility ofN. tenuisfemales at all esti-mated low-lethal concentrations. Chlorpyrifos seriously compromised predator orientation towards a host plant even at LC1,while the same effect was observed for lambda-cyhalothrin and spinosad solely at LC30. Lambda-cyhalothrin (at all concentra-tions) and chlorpyrifos (at LC10and LC30) also affected the time taken byN. tenuisfemales to make a choice.CONCLUSION: The results indicate that all three insecticides can be detrimental toN. tenuisand should be avoided when pres-ence of the predator is desirable.