EFFECTS OF HIGH-TEMPERATURE SHOCKS ON THE DEVELOPMENT AND BIOLOGY OF TRICHOGRAMMA-BRASSICAE [HYM, TRICHOGRAMMATIDAE]

Trichogramma brassicae Bezdenko is used throughout Europe as an effective biological control agent against the European corn borer (Ostrinia nubilalis Hubner). However, in certain climatic regions, the biological control exerted by this parasitoid is less effective. High temperatures inside the released capsules are suspected to have a negative influence on the parasitoids. To simulate these adverse conditions, we applied heat shocks (35-degrees-C and 44-degrees-C) for 6 hours to pupae of Trichogramma brassicae at two periods: white pupae and melanized pupae. The results showed the susceptibility of both the white pupae and melanized pupae, especially at 44-degrees-C. At this temperature, the adults (G0 generation) derived from pupae treated at any age showed reduced longevity and fecundity. Moreover, those descended from treated melanized pupae showed an emergence rate lower than that of the control. These effects reduced to half and more the parasitic efficiency of the G, generation. For the progeny (G1 generation), we observed a decrease of the female ratio : 38 % for the progeny of adults derived from treated melanized pupae ; 88 % for the progeny of those derived from treated white pupae. In that condition, the G1 generation, almost totally male, could not have any parasitic activity.