Side-effect of integrated pest management and conventional spraying on the composition of epigeic spiders and harvestmen in an apple orchard (Araneae, Opiliones)

The effect of two different integrated pest management (IPM) practices and conventional spraying (CHEM) on the composition of epigeic spiders and harvestmen in an apple orchard was investigated over 4 years. Conventional spraying included more frequent and nonselective pesticide applications, whilst IPM plots were treated with selective pesticides and less frequently. One of the IPM plots was undersown with various plantings, the other with grass, and the plot under conventional spraying was covered with weeds. In total, eight species of harvestmen and 65 species of spiders were recorded whose abundance peaked in spring and autumn. Arachnids were on average over the 4 years less abundant on both IPM plots than on CHEM which seems to be due to lower plant density of weed cover. Seasonal oscillations were only slightly different in particular seasons between plots, in particular during spraying. In 1992 the arachnids were a little more abundant on the conventional spraying plot, in 1993 on IPM plots and during subsequent 2 years the difference diminished. The seasonal abundance appeared to be influenced by herbicide applications. Species diversity of all plots were higher than in crop fields, but did not reveal disagreement between plots. The numerical hierarchical classification (TWINSPAN) detected that the composition of arachnids was influenced in particular by annual variation. The arachnid assemblages of the studied plots were not found to be markedly different during the whole study. The effect of IPM practices and conventional spraying on the composition of epigeic arachnids was far less apparent than it was in arboreal species. However, nearly 20% of spiders were found common with crown stratum. Some of them occupied both strata, a few occurred in epigeon only accidently, while others moved vertically during the season. Thus the epigeic fauna seems to support arboreal spiders.