Sub-lethal effects of two pyrethroids on biological parameters and behavioral responses to host cues in the egg parasitoid Telenomus busseolae

The present study was undertaken to investigate possible integration of synthetic pyrethroids with biological control of Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) by the egg parasitoid Telenomus busseolae Gahan (Hymenoptera: Scelionidae). The effects of two commonly used synthetic pyrethroids, deltamethrin (Decis Jet 15 EC) and cyfluthrin (Bayteroid 5 EC), on the parasitoid were studied. Lethal concentrations (LC25) were estimated for both insecticides, and their sub-lethal effects on some biological parameters and behavioral responses to different kairomonal cues mediating host location were investigated. Parasitoid females exposed to cyfluthrin (LC25) parasitized significantly fewer eggs than untreated females, whereas neither the level of emergence from parasitized eggs nor the sex ratio of the offspring was affected by the insecticides. None of the above biological parameters were significantly affected by deltamethrin (LC25). Both insecticide treatments reduced the longevity of the parasitoids. The effects of both insecticides (LC25) on the behavioral responses of parasitoid females to the sex pheromone of S. nonagrioides, which acts as a long-distance kairomone, were investigated in a Y-tube olfactometer. Cyfluthrin-treated parasitoids failed to respond to the host pheromone, whereas deltamethrin-treated females responded similarly to untreated females. In addition, sub-lethal effects of pyrethroids on parasitoid arrestment behaviors were evaluated in an open arena containing abdominal scales from virgin female moths, which are a source of short-distance kairomone for the parasitoid. No significant differences in arrestment behaviors (residence time, linear speed) were found. Based on our results, possible consequences of treating maize with cyfluthrin or deltamethrin on the effectiveness of surviving T. busseolae in the field are discussed.