1999. The Journal of Arachnology 27:531-538 ABUNDANCE OF SPIDERS AND INSECT PREDATORS ON GRAPES IN CENTRAL CALIFORNIA Michael J. Costello!:Costello1: University of California Cooperative Extension, 1720 South Maple Ave., Fresno, California 93702 USA Kent M. Daane: Center for Biological Control, Division of Insect Biology, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 USA ABSTRACT We compared the abundance of spiders and predaceous insects in five central California vineyards. Spiders constituted 98.198.1%% 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 camea,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?per­ centage of predaceous insects (e.g., lacewings) may reflect the lack of preferred prey (e.g., aphids) on grapevines.grape vines. Spiders are important predators in agroe­agroe? ported population densities of the most cosystems (reviews in Nyfeller & Benz 1987; abundant spiders (Misumenops spp.) found on Nyfeller et al. 1994). Many researchers have Arizona cotton,eotton, presenting predaceous insects provided descriptions of spider species abun­abun? as overall percentages but not itemizing for dance or composition in a variety of agroe­agroe? different taxonomic groups. In these publica?publica­ cosystems (e.g., Bishop 1980; Dean et al. tions, the amount of detail presented reflects 1982; Agnew & Smith 1989; Bardwell & Av­Av- the focus of the research, depending in part erill 1997; Wisniewska & Prokopy 1997). upon the breadth of the predator taxon being Other researchers have provided qualitative studied. More commonly, researchers present observations on the abundance of spiders more detailed descriptions of the predaceous (Carroll & Hoyt 1984) or recorded spider pre?pre­ insect fauna, while spiders are grouped to­to? dation events (Reichert & Bishop 1990; Ny?Ny­ gether and data presented as an overall mean, feller et al. 1992). However, it is less common numerical rank or percentage of the number for researchers to compare spider abundance collected (e.g., Roach 1980; Knutson & Gil­Gil- to that of to that of predaceous insects. Those studies strap 1989; Royer & Walgenbach 1991; Bra­Bra- that have analyzed the relative abundance of analyzed man & Pendley 1993). Few studies have pro?pro­ all predaceous arthropods vary considerably predaceous arthropods vary considerably vided equivalent comparisons of spiders and in the presentation of the data. For example, presentation example, predaceous insects at the genus or species lev­lev? MacLellan (1973) reported on predaceous ar­ar? (1973) reported predaceous el (but see Breene et al. 1989). thropods collected on apples in southeastern thropods apples In vineyards, several researchers have cat­cat- Australia, presenting numbers of spiders col­col? presenting spiders aloged the abundance of predaceous arthro­arthro? lected by size and numbers of predaceous in­in? by predaceous pods on grapevines. In southern Germany, sects collected by family. Plagens (1983) re- by family. Plagens (1983) Buchholz & SchmftSchruft (1994) presented num­num? bers of predaceous insects by family, identi­identi- 1 fying salticids to species and thomisids to ge­ 1 Current address: Costello Agricultural Research & fying species ge? Consulting, PO.~O. Box 165, Tollhouse, California nus, but leaving most spiders unidentified. In 93667 USA. California vineyards, spider species composi- 531 532 THE JOURNAL OF ARACHNOLOGY tion, relative abundance and seasonal occur­occur? date, samples were taken between 0700-1200 rence were described by Costello & Daane h PDT. Samples from the .replicatedreplicated cover (1995) and Roltsch et a1.al. (1998), but neither crop studies were pooled across treatments study included data on .predaceouspredaceous insects.insects. and sample dates. A total.oftotal of 100 samples was Here, we present data that compare the rela­rela? taken from the Reedley vineyard, 180 from tive abundance of spiders to predaceous in­in? the Del Rey vineyard and 120 from the Parlier sects on grapevines in California's central val­val- vineyard (one season each). A total of 243 ley. samples was taken from the Ripperdan vine­vine? yard and 360 from the Woodbridge vineyard METHODS (two seasons each). Voucher specimens were Study sites.-sites.?TheThe data presented are from deposited at the Essig Museum at the Univer­Univer? five central valley vineyards that were sam­sam? sity of California at Berkeley. pled from 1995-1997. Grapevine cultivar and For each vineyard and sampling method, cultural practices varied among the sites. In means were transformed to numbers of pred?pred­ 1995, three vineyards in Fresno County were ators per vine. Seasonal abundance of spiders sampled: a raisin vineyard (cultivar "Thomp­"Thomp? and predaceous insects were plotted against son Seedless" near Del Rey, California)CaHfornia) a ta­ta? cumulative degree days above 10°C10 ?C (the low­low? ble grape vineyard (cultivar "Ruby Seedless" er developmental threshold for grapevines) near Reedley, California) and a juice vineyard from 1 January, for each sample year. (cv "Thompson Seedless" near Parlier, Cali­CaH? RESULTS fornia). In 1995 and 1996, a winegrape vine­vine? yard in San Joaquin County (cv "Cabemet"Cabernet We collected a total of 13,348 spiders (2781 Sauvignon" near Woodbridge, California) at Del Rey, 6468 at Woodbridge, 1273 at Rip­Rip? and, in 1996 and 1997, a juice vineyard in perdan, 679 at Parlier and 2147 at Reedley) Madera County were sampled (cv "Thompson and 219 predaceous insects (36 at Del Rey, Seedless" near Ripperdan, California). These 122 at Woodbridge, 6 at Ripperdan, 43 at Par­Par? sites were part of studies designed to deter­deter? lier and 12 at Reedley). Over all sites, spiders mine the impact of cover crops on vineyard constituted 98.198.1%% of all predators collected, insect pests and their natural enemies (see whereas the insect predators comprised just Costello & Daane 1998b; Daane & Costello 1.6% of total predators. At individual sites, 1998). All of the study sites were bordered by spiders comprised at least 94% of predators cultivated vineyards or orchards. collected, with the highest percentage at Rip­Rip? In each year, all vineyards received multiple perdan (99.5%) and the lowest at Parlier applications of sulfur for control of powdery (94.0%) (Table 1). Predaceous insects com­com? mildew, Uncinula necator Burrill, and one or prised 6.0% or less of all predators at each two applications of cryolite (sodium alumi­alumi- site, the highest percentage found at Parlier nofluoride) for control of omnivorous leaf­leaf- (5.9%) and the lowest at Ripperdan and Reed­Reed? roller, Platynota stultanastultanaWalshingham Walshingham 1884 ley (0.5%) (Table 1). The only other arthropod (Lepidoptera, Tortricidae), and grapeleaffold­grapeleaf fold- predator collected was Anystis agilis (Banks er, Desmia funeralis (Hubner(Hiibner 1796) (Lepidop­(Lepidop? 1915) (Acari, Anystidae), a predaceous mite tera, Pyralidae). that feeds on insects as opposed to spider SampUng.-CostelloSampling.?Costello & Daane (1997) pro?pro­ mites. Only 17 Anystis agilis.agilis were collected, vide a detailed description of sampling meth­meth? all at the Reedley site, comprising 1.5% ofofthethe ods. In brief, the Del Rey,Ripperdan,Rey, Ripperdan, Parlier predators collected there. and Woodbridge vineyards were sampled by Spiders.-EightSpiders.?Eight species from six families 2 shaking a 0.89 mm2 section of vine foliage into constituted >90% of all spiders collected. By a funnel shaped collector, and the Reedley family, these were: (1) Miturgidae: Cheira­Cheira- vineyard was sampled by shaking the foliage canthium inclusum (Hentz 1847); (2) Corin­Corin- of two grapevines onto a drop clothcloth and col­col? nidae: Trachelas pacificus (Chamberlin & Ivie lecting all predators ·withwith small battery-pow-battery-pow­ 1935); (3) Theridiidae: Theridion dilutum ered vacuums. Samples were taken monthly, Levi 1957 and Theridion melanurum Hahn from May to September, except for the Rip­Rip? 1831; (4) Oxyopidae: Oxyopes scalaris Hentz perdan vineyard in 1996,.1996, which·.which was.was sampled 1845 and Oxyopes salticus Hentz 1845; (5) from July to September. On each sampling Agelinidae: Hololena nedra Chamberlin & for () Table 0 each CIl 1.?Mean site. ~ 0 Table I.-Mean season-wide density and population percentage of predatory arthropods in five central valley vineyards, 1995-97, data pooled acrossSuperscript years f<:o for each site. Superscript "1" indicates Theridion dilutum and Theridion melanurum. Superscript "2" indicates Oxyopes scalaris and Oxyopes salticus. 0 season-wide > Ripperdan Woodbridge Del Rey Reedley Parlier > Predator Mean (±SE) % Mean (±SE) % Mean (±SE) % Mean (±SE) % Mean (±SE)