Some observations on overwintering of spiders (Araneae) in two contrasting orchards in the Czech Republic

Abstract

Overwintering of spiders was studied by means of cardboard trap bands in two different orchards in the Czech Republic, an apple under integrated pest management (in 1993) and an abandoned pear (in 1995). Twenty-seven species of spiders were found to overwinter on tree trunks. The overwintering composition was not very similar to the composition of arboreal spiders detected during spring and summer by beating tree branches. For example, Clubiona specimens occur on ground and canopy in summer but prefer tree trunks to pass winter. Except Clubionidae, three other families, Philodromidae, Theridiidae and Dictynidae, predominated in trap bands. The two study orchards differed in species composition of overwintering spiders as a result of the orchard type (commercial versus abandoned), temporal variation, and the bark structure (rough in pear and smooth in apple). The commercial apple orchard was predominated by small insecticide-tolerant spiders, Theridiidae and Dictynidae, whereas the abandoned pear orchard was dominated by large susceptible species of Clubionidae and Philodromidae. Installation of cardboard bands on young trees with smooth bark may significantly support overwintering of spiders. Distribution of spiders among trap bands of the IPM orchard showed a clumped pattern. It appeared that populations under pressure are spatially distributed. A significant negative correlation was observed between large spiders (Philodromidae) and small ones (Theridiidae and Dictynidae) resulting presumably from interspecific predation. Non-linear models were fitted to these relationships. The relationship between Philodromidae : Clubionidae, Clubionidae : Theridiidae, and Clubionidae : Dictynidae could not be described by correlation. Thus, it is concluded that Clubionidae do not interact with other spiders at overwintering sites.