Résumé
Using the methodology of the French AFPP/CEB guideline no. 167 for testing side effects of pesticides on Typhlodromus pyri, we review the results obtained with laboratory trials for more than 120 pesticides. Most of the insecticides/acaricides tested were found to be toxic and most of the fungicides non-toxic or slightly toxic. These results provided a good indication of the toxicity assessed in field trials. To put this relation to the test, we carried out a more in-depth study on the fungicide mancozeb and its toxicity to phytoseiids in vineyard and orchard. Side effects of this fungicide were studied on T. pyri in the laboratory and in 4-year field trials in several grape crops. In vineyards where mancozeb had commonly been used over the years, this fungicide is generally slightly toxic. However, in plots where it had never been used, its effect on populations of T. pyri was more pronounced and varied from moderately toxic to toxic. Despite its intrinsic toxicity, populations were never eradicated. Laboratory results confirmed the field trial results. Even though toxicity of mancozeb is higher in lab trials, a significant correlation was established between field and laboratory results for all strains of T. pyri. It is striking to observe that – despite the intrinsic toxicity of not only mancozeb, but also pyrethroids and organophosphates – densities of T. pyri and Amblyseius andersoni in grape crops in the Region Midi-Pyrénées are commonly high. Our laboratory tests indeed showed that strains of these two species are resistant to deltamethrin, ë-cyhalothrin, and chlorpyriphos-ethyl, which probably explains their abundance in grape crops in this area.