effects of eight insecticides on the foraging behavior of the parasitoid wasp Cotesia vestalis

In natural environments, parasitoid wasps can find host-infested plants by detecting herbivore-induced plant volatiles (HIPVs). However, in agroecosystems, their foraging behavior may be inhibited by the odors of insecticides sprayed on the host-infested plants. In this study, we investigated the effects of the following eight insecticides on the flight response of female parasitoids (Cotesia vestalis) to Brassica rapa infested with the larvae of their host, the diamond-back moth (Plutella xylostella). We found that odors from etofenprox, methomyl, and malathion strongly affect the parasitoid's foraging behavior via HIPVs, while permethrin, emamectin benzoate, and clothianidin do not. Alanycarb and diazinon are intermediate between them. We then investigated, using host-infested plants treated with diazinon or distilled water, how long the insecticide affected their flight response. At 1 and 24 h after spraying, C. vestalis females preferred infested, water-treated plants to infested, diazinon-treated plants. However, at 72 h after spraying, they did not discriminate between these plants, suggesting that the inhibitory effect disappears at least 72 h after spraying.