Spiders and Ants of Texas Citrus Groves

Abstract

Spider species (Araneae) inhabiting citrus ecosystems have been collected and identified in Florida (Muma 1975, Mansour et al. 1982) and California (Carroll 1980), but there is no comparable information from Texas. The seasonal abundance of selected arthropod predators was studied by Fuchs & Harding (1976) in southern Texas, and spiders were identified only to order. Except for ant species regarded as potential pests of citrus (Schuster & Dean 1957, Dean et al. 1983), the identity of ant species occurring in citrus ecosystems remains largely obscure. Spiders and ants were collected from southern Texas citrus ecosystems from August 1990 to March 1991 (a total of 12 sampling dates) over a wide area of Hidalgo and Cameron counties by using hand collection, an aspirator and sweep net. Species were gathered from citrus leaves, branches, trunks and from the ground surrounding the trees on a qualitative basis; no quantitative collection methods were used. With the addition of three spider species collected from citrus trees by one of the authors in 1983 (D.A.D.), and two species of ants listed in Dean et al. (1983), a total of thirty three species of spiders from 13 families and twelve species of ants were identified (Table 1). Comparing spider species using only relative frequency of discovery, 36% of the total number of spiders collected were orb weavers of the family Araneidae, with 63% of these belonging to the species Metazygia zilloides (Banks). The next most numerous family was comb-footed spiders (Theridiidae, 12%), followed by crab spiders (Thomisidae, 11%), jumping spiders (Salticidae, 11%), wolf spiders (Lycosidae, 9%), long-jawed orb weavers (Tetragnathidae, 4.5%), ground spiders (Gnaphosidae, 4.5%), horizontal orb weavers, sac spiders and ghost spiders (Uloboridae, Clubionidae and Anyphaenidae, respectively, all with 3%), mesh web weavers, pirate spiders and lynx spiders (Dictynidae, Mimetidae and Oxyopidae, respectively, all with 1%). Relative numbers of ant individuals were not compared, but the tropical fire ant, Solenopsis geminata (Fabr.) was observed in citrus groves more recurrently than any other. The tropical fire ant, although a predator of insect pest species of other crops, is considered a potential pest of citrus by Dean et al. (1983). Solenopsis geminata is capable of occasionally girdling citrus trees, may often tend honeydew excreting insect pests like aphids, mealybugs and brown soft scale (which may interfere with their parasitoids and predators), and can attack pickers and other field workers (Dean et al. 1983). Most of the other ants, except Atta texana and Pogonomyrmex barbatus, also tend aphids. There have been few studies of spider predation in citrus groves and most of these used a mixture of field and laboratory observations. Mansour & Whitcomb (1986) found spiders, largely the sac spider Cheiracanthium mildei L. Koch, to be important controlling factors of the barnacle scale, Ceroplastes floridensis Mask (Homoptera: Coccidae) in citrus groves in Israel. Carroll (1980) suggested that sac spiders were the most important spiders in terms of control on citrus arthropod pests, and Cherrv & Dowell