Laboratoire de Neurobiologie Comparée Des Invertébrés, INRA, BP 23, 91440 Bures-Sur-Yvette, France.
Parasitic wasps are important regulators of pest insects. In many species, the recognition of chemical signals is essential to find specific hosts. This function may be impaired by parasitoids surviving insecticide exposure. We aimed to document this assumption. In laboratory conditions, the behaviour of the Hymenopterous parasitoid Aphidius ervi surviving low doses of the pyrethrinoid lambda-cyhalothrine was examined on a host aphid, Myzus persicae, on oilseed rape. Female Aphidius were exposed by contact with dry residues of the active ingredient on glass, at the CL 0.1 and the CL 20. In a four-armed olfactometer, control females were innately attracted to the odour of Myzus-infested plants. This response was much decreased by exposure to the CL 0.1 but not the CL 20. The effect disappeared within 24h. Females with a previous oviposition experience on the infested plant showed a longer response to the odour than naive individuals. These experienced responses were not impaired by the insecticide. Oviposition activity was slightly decreased in treated individuals. So this work shows that behaviours essential to the parasitoid's reproduction can be impaired by very low quantities of insecticide. It also points out that such sublethal effects are difficult to predict because they are not correlated to insecticide concentrations and they depend on individual parameters such as experience.