Modifications of Trichogramma Behaviors During the Exploitation of Host Patches Induced by the Insecticide Chlorpyrifos

Parasitoid species are key species because they regulate numerous insect species, including pests. An efficient infestation of hosts is critical to the development of parasitoid populations. In this article, we investigate the effects of the widely used insecticide chlorpyrifos on the exploitation of a patch of host by a parasitoid, Trichogramma brassicae. We show that chlorpyrifos increased the efficiency of parasitoid females in the infestation of the first host egg by decreasing its super-parasitization. Except for the first egg, all infested eggs were infested only once by both control and treated females; therefore, the insecticide did not impede the detection of a host that had already been infested. We did find that the insecticide affected the mode of rejection of infested eggs. At the beginning of the exploitation of the patch, females exposed to the insecticide made more antennal rejections than controls but eventually made more ovipositor rejections. These results suggest that the insecticide initially stimulated the antennal perception of the infested host but finally led to the saturation of this perception. Parasitoids compensated for this loss of antennal perception via ovipositor perception of infested eggs. This switch of behavior corresponds to a decrease in efficiency, as it is much more time consuming; therefore, females exposed to the insecticide had to stay longer on the patch for an equal rate of exploitation relative to controls. The infestation of host eggs is a crucial behavior for parasitoids, enabling their reproduction and the development of their species. By decreasing the antennal recognition of infested eggs, chlorpyrifos continues to be detrimental even when parasitoids survive exposure.