Effects of insecticides on the foraging behaviour and survival of Cotesia vestalis, a larval parasitoid of the diamondback moth, Plutella xylostella

Abstract

The effects of the insecticides etofenprox, malathion, diazinon, methomyl, alanycarb, clothianidin and emamectin benzoate on the foraging behaviour and survival of Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) were investigated in the laboratory. The period required for C. vestalis females to reach P. xylostella-infested Komatsuna (Brassica rapa) plants treated with etofenprox, methomyl or malathion was significantly longer than that to infested plants treated with emamectin benzoate or clothianidin; and the period to reach alanycarb or diazinon-treated plants was intermediate between them. The period to reach emamectin benzoate- or clothianidin-treated plants was not significantly different from that to distilled water-sprayed plants, suggesting that etofenprox, methomyl and malathion have strong inhibitory effects on the flight response, whereas the inhibitory effects of alanycarb and diazinon are relatively weak. By contrast, emamectin benzoate and clothianidin showed no inhibitory effect. The time of residency on the clothianidin-treated plants was significantly longer than that on other insecticide-treated plants (etofenprox, methomyl, alanycarb, malathion or diazinon), with the time of residency on emamectin benzoate-treated plants being intermediate between them. These results suggest that etofenprox, methomyl, alanycarb, malathion, and diazinon have a strong inhibitory effect on host-searching behaviour, while emamectin benzoate and clothianidin have a relatively weak effect. Furthermore, the mortality of wasps after foraging on the clothianidin-treated plants was significantly higher than after foraging on other insecticide-treated plants (etofenprox, methomyl or malathion), with subsequent mortality on alanycarb-, diazinon- and emamectin benzoate-treated plants being intermediate between them. Our results suggest that subsequent mortality increases with decreased inhibitory effect on the foraging behaviour of C. vestalis.