A field study to assess the effects of insecticides used to control the Colorado beetle in potato on aphid antagonists

Abstract: The effects of five insecticides used to control the Colorado beetle in Potato were assessed in a field trial on aphid-specific beneficial arthropod fauna, mainly parasitic hymenoptera, ladybirds, lacewings and hoverflies. The insecticides were applied at their commercial rate at the end of July, when beneficial arthropods and aphid population were at their maximum. The effects on aphid populations were followed by visual inspection up to 33 days after treatment and aphid natural enemies were collected by the beating methods 2, 7 and 18 days after treatment.The results of the beatings showed that all insecticides had an impact on both ladybird and hoverfly larvae. The impact on ladybird was limited for azadirachtin, rynaxypyr and spynosin B while cypermethrin and thiametoxam were more toxic. Hoverfly were more sensitive to all the insecticides tested, with population reduction > 50% compared to the control. Spynosyn B also reduced the parasitism of aphid by Aphidius wasps at DAT2, determined by dissection of aphid collected during the beatings, but the effects were limited in duration and no significant effects were observed later. The other product had no or limited effects on aphid parasitism.The effects on aphid populations revealed that no insecticides were promoting aphid outbreak by directly impacting natural enemy’s populations. However, the beneficial arthropods activity was so high that even high reductions of populations had no impact on aphid population in this particular field site.These results are discussed in term on beneficial populations and IPM, taking into accounts both direct effects and long-term effects.