Sub-lethal effects of deltamethrin on walking behaviour and response to host kairomone of the egg parasitoid Trissolcus basalis.

The lethal doses of the pyrethroid deltamethrin were estimated for the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), and the sub-lethal effects of an LD25 on female walking behaviour were evaluated. Linear speed of treated parasitoids was reduced compared with that of untreated ones for a period of up to 24 h. The sub-lethal effects of deltamethrin on parasitoid response to patches contaminated by a contact kairomone from its host, Nezara viridula L (Heteroptera: Pentatomidae), was also evaluated. Both treated and untreated parasitoids responded to host-contaminated patches by increasing residence time and decreasing linear speed. However, treated females showed a significantly lower residence time compared with untreated females. Both treated and untreated females showed a similar decrease over time in the proportion of time spent in the host-contaminated patch. Hence, we hypothesise that the sub-lethal effect of deltamethrin on host foraging may decrease T basalis efficacy in controlling N viridula.