Increase of the behavioral response to kairomones by the parasitoid wasp Leptopilina heterotoma surviving insecticides

Hymenopterous parasitoids are key species involved in the regulation of insect populations. Kairomone perception is an important step leading to host parasitization. The massive use of insecticides induces environmental pollution that can interact with the reproduction of parasitoids. In this work, we have determined the sublethal effects of two insecticides, an organophosphorus (chlorpyrifos) and a pyrethroid (deltamethrin), on the arrestment, by host kairomones, of female parasitoids surviving an LD 20 for 24 h. The behavior of the parasitoids has been recorded with a video-computerized system. The analysis of the behaviors in control conditions versus exposed to an LD 20 have shown that both insecticides significantly increased the arrestment of parasitoids by kairomones. This increase was not followed up by a modification of the kinetics of the behavior. In both control and exposed conditions, parasitoids regularly increased their residence time on the kairomone patch indicating that no saturation to kairomones had occurred. In a field situation where hosts could be scarce, this increase in arrestment could be advantageous for parasitoids by increasing their host finding.