Effect of exclusion nets on spider diversity and composition in IPM apple orchard

Abstract: Spiders are one of the most abundant natural enemies in apple orchards and have an important role in the biological control of harmful arthropods. Recently coloured shade nets to improve the utilization of solar radiation by fruit trees and to exclude pest species have been introduced in practice. While the coloured netting in apple orchards had a positive effect on fruits, the aim of the our research was to analyse the effects of the nets on spider diversity and species composition. The ground dwelling spider assemblage was sampled by pitfall trapping. Pitfall traps were placed under trees covered by four types of exclusion photo selective nets and uncovered control trees in an untreated experimental plot of an IPM apple orchard. The study was spatially replicated in three rows. During the investigation period 456 individuals belonging to 26 species and 12 families of spiders were collected. Two wolf spider (Araneae, Lycosidae) species were dominating the assemblages: Trochosa robusta (Simon 1876) and Hogna radiata (Latreille 1819) comprised 45% of the total adult catch, and these were the only species that occurred in all treatments. There was no difference either between the abundance, species richness or the species composition of spiders in the treatments. The study strongly indicates that insect exclusion nets have no negative effect on ground dwelling spider assemblages.