Susceptibility of Aphelinus mali (Haldeman) to different active ingredients commonly used in organic apple orchards in Trentino (North Italy)

Aphelinus mali (Haldeman) is the most important biological control agent of woolly apple aphid (WAA) Eriosoma lanigerum (Hausmann), a serious pest of apples. The amount of products used in apple orchards could compromise the effectiveness of A. mali on its biological control. The rate of parasitism reaches high levels (80-90%) in late summer when part of the damage has already been caused. In Trentino region (Italy) the first peak of flight of A. mali is in the post-flowering period, although limited in size and is essential for an exponential flight increase and the consequent culmination of the parasitisation ratio in summer, generally at the end of July. It is essential to avoid pesticides toxic to A. mali after flowering but also other active substances that can reduce A. mali activity. For these reasons, we tested several plant protection products to evaluate potential compatibility in integrated and organic pest management programs. The direct (topical sprays in Potter’s Tower) and residual (leaf residue) effect of insecticides and fungicides on the adult stage of this parasitoid were investigated under laboratory conditions. The active ingredients used in trials were deltamethrin (as a chemical referent), azadirachtin, sulphur and Lime Sulphur. The products were tested at recommended field rates. A treatment with water was used as control in both experimental trials. The insects’ mortality rate on direct effect in Potter’s Tower was different only for the deltamethrin at different control timing. Deltamethrin caused the highest mortality also in residual effect than the other products. After 3 and 7 days from the treatment no product were caused mortality