Spiders as biological controller in apple orchards infested by Cydia spp.

Spiders have been commonly considered as polyphagous predators. For this reason, it has been argued that spiders may not be efficient in controlling pests. However, in recent years it has been demonstrated that they are able to significantly decrease the damage caused by insects to harvest. In this paper we present some preliminary results of a field experiment that has taken place in 2007, in a biological apple orchard at Caraglio (Cuneo, North-Western Italy). The aim of the experiment was to study the potential reduction of the damage caused by Cydia spp. (Lepidoptera: Tortricidae) to apples by increasing the population size of spiders living on trees by offering them additional shelter space through the provision of artificial shelters (polyethylene bark-traps) during wintertime. The spider assemblage was found to be strongly dominated by Anyphaena accentuata (43%), followed by Dictyna arundinacea (20%) and Philodromus spp. (8%). Compared to control, the total number of spiders increased significantly in trees provided with artificial shelter and trees with such device showed lower frequency of damaged apples. Results from this preliminary study suggest that habitat manipulation in apple orchards may increase the population size of bark dwelling spiders and thus increase their potential preying efficiency.