Side-effect of integrated pest management and conventional spraying on thecomposition 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 harv estmen in an apple orchard was investigated over 4 years. Conventional spra ying 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 sligh tly different in particular seasons between plots, in particular during spr aying. In 1992 the arachnids were a little more abundant on the conventiona l spraying plot, in 1993 on IPM plots and during subsequent 2 years the dif ference diminished. The seasonal abundance appeared to be influenced by her bicide applications. Species diversity of all plots were higher than in cro p fields, but did not reveal disagreement between plots. The numerical hier archical classification (TWINSPAN) detected that the composition of arachni ds was influenced in particular by annual variation. The arachnid assemblag es 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 c omposition of epigeic arachnids was far less apparent than it was in arbore al species. However, nearly 20% of spiders were found common with crown str atum. Some of them occupied both strata, a few occurred in epigeon only acc idently, while others moved vertically during the season. Thus the epigeic fauna seems to support arboreal spiders.