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

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. ABSTRACT As part of an investigationto estimate the effect of resident spider populations on Erythroneura variabilis 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), TrachelCMpacificus (Chamberlin and Ivie), Theridion dilutum Levi, Theridion melan- urum Hahn, OX'lopes scalaris 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 diversityvaried among vineyard sites. In 4 vineyard sites, hunting spiders (C. inclusum, T. pacificus, OX'l0pes 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 similaritybe- 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 similarityamong 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.