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Trichogramma brassicae Bezdenko is used throughout Europe as an effective biological control agent against the European corn borer (Ostrinia nubilalis H/ibner). 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 *C and 44 ~ 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 *C. At this temperature, the adults (Go 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 thc control. These cffects reduced to half and more the parasitic efficiency of the Go generation. For the progeny (G t generation), wc 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 G~ generation, almost totally male, could not have any parasitic activity. KEY-WORDS : parasitoid, biological control, heat shock.In Europa, the use of Trichogramma (Hym. oophagous parasitoids) against the European corn borer Ostrinia nubilalis Hiibner (Lep., Pyralidae) (Hawlitzky et al., 1987) has been spreading for some years. In certain regions of France, the entomophagous insects are released when the corn is still small and has few leaves, thus exposing the capsules containing the developing Trichogramma to adverse climatic conditions, especially strong sunshine.To simulate these climatic conditions, found in the field --especially in the Paris region where measurements taken inside the capsules showed that the temperature could reach 35 ~ or even 44 *C for 6 hours per day --single heat shocks of 35 ~ or 44 ~ were applied in the laboratory for a duration of 6 hours, during the pupal instar of T. brassicae.Two ages were chosen : white pupae with red eyes and red ocelli (WP), and melanized pupae (MP). These are the stages used for field releases. The first aim was to determine the effects produced by the rise in temperature on individuals originating from the pupae released in nature, and on their progeny. The second aim wa~ to compare the susceptibility of the two pupal periods to these temperature shocks (Chihrane, 1989).

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Volatile chemicals emanating from the different developmental stages ofOstrinia nubilalis Hübner (Lepidoptera, Pyralidae) increase the mobility ofTrichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) in a linear airflow olfactometer. In this paper, we have demonstrated that airborne chemicals from egg masses and virgin females during calling activity stimulate an intensive search behavior byTrichogramma females. On the other hand, emanations from mated females with extruded abdominal tips do not incite the parasitoid's movement. For the moment we cannot elucidate, with these bioassays, the real role of these kairomones as attractants, guides, stimulants, or retainers.

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