Arachnology 27:531-538 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 per? centage of predaceous insects (e.g., lacewings) may reflect the lack of preferred prey (e.g., aphids) on grape vines. Spiders are important predators in agroe? cosystems (reviews in Nyfeller & Benz 1987; Nyfeller et al. 1994). Many researchers have provided descriptions of spider species abun? dance or composition in a variety of agroe? cosystems (e.g., Bishop 1980; Dean et al. 1982; Agnew & Smith 1989; Bardwell & Averill 1997; Wisniewska & Prokopy 1997). Other researchers have provided qualitative observations on the abundance of spiders (Carroll & Hoyt 1984) or recorded spider pre? dation events (Reichert & Bishop 1990; Ny? feller et al. 1992). However, it is less common for researchers to compare spider abundance to that of predaceous insects. Those studies that have analyzed the relative abundance of all predaceous arthropods vary considerably in the presentation of the data. For example, MacLellan (1973) reported on predaceous ar? thropods collected on apples in southeastern Australia, presenting numbers of spiders col? lected by size and numbers of predaceous in? sects collected by family. Plagens (1983) re1 Current address: Costello Agricultural Research & Consulting, PO. Box 165, Tollhouse, California 93667 USA. ported population densities of the most abundant spiders (Misumenops spp.) found on Arizona eotton, presenting predaceous insects as overall percentages but not itemizing for different taxonomic groups. In these publica? tions, the amount of detail presented reflects the focus of the research, depending in part upon the breadth of the predator taxon being studied. More commonly, researchers present more detailed descriptions of the predaceous insect fauna, while spiders are grouped to? gether and data presented as an overall mean, numerical rank or percentage of the number collected (e.g., Roach 1980; Knutson & Gilstrap 1989; Royer & Walgenbach 1991; Braman & Pendley 1993). Few studies have pro? vided equivalent comparisons of spiders and predaceous insects at the genus or species lev? el (but see Breene et al. 1989). In vineyards, several researchers have cataloged the abundance of predaceous arthro? pods on grapevines. In southern Germany, Buchholz & Schruft (1994) presented num? bers of predaceous insects by family, identifying salticids to species and thomisids to ge? nus, but leaving most spiders unidentified. In California vineyards, spider species composi. rachnology :531-538 BUNDANCE F PIDERS ND SECT EDATORS N RAPES ENTRAL ALIFORNIA ichael . stello!: niversity f lifornia Cooperative tension, 20 uth aple ve., r sno, lifornia 702 SA ent . aane: nter r iological ntrol, ivision f sect Biology, epartment f vironmental ience, Policy d anagement, niversity f lifornia, erkeley, lifornia 720 SA STRACT co pared e spiders predaceous cts tr fornia vineyards. Spiders stituted predators llected. r spiders llected r eight species f spiders, representing ies. s ( heridion t . elanurum) r t t, llowed by iturgid ( heiracanthium inclusu ) agelinid ( ololena e r ). ous cts co prised predators llected, r represented by genera ies. is a ericoferis ( eteroptera, abidae) t on predaceous i t, t ities highest gro ing n. hrysoperla m , hrysoperla nche hrysopa lata ( europtera, hrysopidae) ippodamia convergens (Coleoptera, ccinellidae) r t t early n. i ance spiders ay r r position vineyard predator co unity co pared predaceous ts. suggest percentage predaceous cts (e.g., lace ings) ay t preferred prey (e.g., aphids)