Susceptibility of Aphelinus mali (Haldeman) to different products used in apple orchards in Trentino (Northern Italy)

Aphelinus mali (Haldeman) is the most important biological control agent of woolly apple aphid (WAA) Eriosoma lanigerum (Hausmann), a serious pest of apple. The first adults of A. mali emerge only when the WAA has already gone through one generation, and its innate capacity to increase is considerably lower than its host. In fact, the rate of parasitism reaches high levels (80-90%) in late summer. Furthermore, some plant protection products commonly used in apple orchards could compromise the effectiveness of A. mali on biological control. In Trentino region (Italy), the first flight peak of A. mali usually occurs in the post-flowering period. Afterwards, an exponential flight increases and the consequent culmination of the parasitisation ratio in summer is observed, generally at the end of July. To understand the possible effects of different active substances on A. mali activity, we tested several plant protection products commonly used in integrated and organic pest management programs. The direct treatment effect (topical sprays in Potter’s Tower) of insecticides and fungicides on parasitized mummies (closed, with parasitoid inside) were investigated under laboratory conditions. The products used in trials were Decis®Evo (a.i. Delthametrin, as a chemical referent), a mixture preparation containing Vernoil (paraffin mineral oil) and Thiopron® (a.i. Sulphur), Polithiol® (a commercial formulation of emulsifiable suspension containing paraffin oil) and Pirimor®50 (a.i. pirimicarb). A treatment with water was used as control. The products were tested at recommended field rates. Twigs with parasitized woolly apple aphids were collected at the end of June from an untreated orchard and kept in a cool room until needed. Parasitized mummies were removed from the infested twigs and selected under the stereomicroscope for the Potter’s tower treatments. Forty mummies per thesis were used. The experimental design was replicated and reproduced in two different timings. After the treatment, the mummies were kept in a climatic chamber under constant climatic conditions (25±1°C, 60±5% R.H. and photoperiod 16:8 (L:D). The mummies were examined at 5,7,12,16 days after the treatment and the emergence of adult parasitoids was evaluated. At the same time, a commercial apple orchard was divided in two blocks: untreated and treated with the mixture preparation containing Vernoil (paraffin mineral oil) and Thiopron (a.i. Sulphur), at BBCH 01. After that, treated and untreated Eriosoma lanigerum colonies were collected from the field, selected under stereomicroscope and positioned in an aerated box until A. mali adults completely emerged. The results of direct effect trial in Potter’s Tower showed that the commercial formulation containing paraffin oil and sulphur (Polithiol) caused a lower A. mali flicker rate than the other products. The preliminary field results showed a lower percentage of parasitoid flicker on mummies collected in the plot subjected to the winter treatment. Further studies are necessary to understand if insecticides and fungicides can influence the first peak of A. mali flight in the post-flowering period and the consequent parasitisation ratio in summer