A large field trial to assess the short-term and long-term effects of several 4 insecticides used to control the pollen beetle on parasitic hymenoptera in oilseed rape

Abstract: The effects of different mixtures containing one fungicide and one insecticide,some of them previously known to have synergistic effects on bees, on adults of the parasiticwasp Aphidius rhopalosiphi, protonymphs of the predatory mite Typhlodromus pyri andlarvae of the ladybird Adalia bipunctata were assessed in the laboratory. LD50 tests on glassplates using standard methods were used for the two first species while LD50 was assessed onladybird larvae following topical application of 0.5 μl product droplets. The mixturesprochloraz + lambdacyhalothrine, epoxyconazole + thiacloprid, pymetrozine + fluazinam andtaufluvalinate + boscalid, as well as each individual compound, were assessed in one or twosets of five to eight sequential dilutions. The proportions of insecticides and fungicides werebased on normal agricultural practice, keeping the same ratio throughout the dilutions.The results showed that the mixtures prochloraz + lambda-cyhalothrine andepoxyconazole + thiacloprid had a strong synergistic effect on the three species, with anLD50 2.5 to 11 times lower than that of the insecticide alone, while the fungicide testedseparately had no toxicity at all. The LD50 of the two other mixtures was no different fromthe effects of the insecticide alone.These results suggest that the toxicity of several insecticides for beneficial arthropodsoften applied in mixtures with fungicides could be underestimated if they are assessedindividually, as is currently done. Although only a limited number of associations have beentested so far, these results raise questions about the relevance of risk assessment of singleproducts for beneficial arthropods and, by extension, for all non-target species.