Spider predation on rosy apple aphid in conventional, organic and insecticide-free orchards and its impact on aphid populations

Spiders dwelling in the canopy of apple trees may contribute to the control of the rosy apple aphid (Dysaphis plantaginea) in spring. They are expected to be very efficient early in the season during aphid colony establishment. However, their predation on aphids may be impaired by insecticide treatments. In the present study, we aimed to assess the effectiveness of spider predation on D. plantaginea in apple orchards. For this purpose, we sampled a total of 1281 canopy spiders in 8 orchards under IPM (Integrated Pest Management), organic or insecticide-free management in the early and mid-season. DNA analyses of the spider guts with specific D. plantaginea PCR primers were performed to estimate which taxa had eaten this aphid pest in the early and mid-season. Lastly, we assessed the effectiveness of aphid suppression by spiders in insecticide-free orchards during these two periods. The most abundant spiders collected belonged to the Philodromidae, Salticidae and Anyphaenidae families. Spiders were more abundant in the insecticide-free orchards than in the other orchards in the mid-season but not in the early season. The positive detection of D. plantaginea DNA was observed in 8 out of the 12 most abundant families and occurred in all orchards. The probability for a spider to be found positive increased with the abundance of aphids and was higher in the insecticide-free than in the other orchards. It did not depend on the spider prosoma size. Lastly, the increase in the number of aphid colonies early in the season was negatively related to the abundance of Philodromus spp. All these results showed that numerous spider taxa participate in the control of D. plantaginea in organic, conventional and IPM orchards and that Philodromus spp. may be particularly efficient in the early season where arthropod communities are not disturbed by insecticides.