Spider (Araneae) Species Composition and Seasonal Abundance in San Joaquin Valley Grape Vineyards

Environ. Entornol. 24(4): 823-831 (1995) ABSTRACT As part of an investigation to estimate the effect of resident spider populations on Erythroneura vatiabilis Beamer, spider species composition, relative abundance, and sea­ sonal occurrence were determined. Spiders were sampled monthly during the 1992 and 1993 growing seasons; their numbers were pooled and analyzed for species diversity using the Renkonen index of similarity and cluster analysis. Twenty-seven species of spiders were re­ corded, representing 14 families. The most common species were Cheiracanthium inclusum (Hentz), TrachelCM pacificus (Chamberlin and Ivie), Thetidion dilutum Levi, Thetidion melan­ urum Hahn, OXIJopes scalatis Hentz, Oxyopes salticus Hentz, Hololena nedra Chamberlin and Ivie, and Metaphidippus vitis (Cockerell). Three species (C. inclusum, T. dilutum, and T. melanurum) constituted >30% of all spiders collected; however, species diversity varied among vineyard sites. In 4 vineyard sites, hunting spiders (C. inclusum, T. pacificus, OXIJopes spp., and M. vitis) dominated the fauna, representing an average of 79.7% of the specimens col­ lected. In the other 3 vineyards, hunting and web-weaving spiders were more equally repre­ sented, averaging 43.5 and 50.0%, respectively, of all spiders collected. Species similarity be­ tween vineyards from both years ranged from 19 to 73% based on the Renkonen index. Similarly, cluster analysis showed a wide separation in species composition among sampled vineyards. The discrepancy in species similarity among sampled vineyards is discussed in ref­ erence to potential prey density and vineyard cultural practices. Seasonal abundance patterns of the 8 most common species are presented and discussed in reference to their respective phenologies.