Abundance of Spiders and Insect Predators on Grapes in Central California

We compared the abundance of spiders and predaceous insects in five central California vineyards. Spiders constituted 98.1% of all predators collected. More than 90% of all spiders collected were from eight species of spiders, representing six families. Two theridiids (Theridion dilutum and T. melanurum) were the most abundant, followed by a miturgid (Cheiracanthium inclusum) and an agelinid (Hololena nedra). Predaceous insects comprised 1.6% of all predators collected, and were represented by six genera in five families. Nabis americoferis (Heteroptera, Nabidae) was the most common predaceous insect, with its densities highest late in the growing season. Chrysoperla carnea, Chrysoperla comanche and Chrysopa oculata (Neuroptera, Chrysopidae) and Hippodamia convergens (Coleoptera, Coccinellidae) were most abundant early in the season. The dominance of spiders may be due to their more stable position in the vineyard predator community compared to predaceous insects. We also suggest that the low percentage of predaceous insects (e.g., lacewings) may reflect the lack of preferred prey (e.g., aphids) on grapevines.