8-1566 April 1987 Distriution and Abundance Patterns of Spiders inhabiting . Cotton in Texas \ I THE TEXAS AGRICULTURAL EXPERIMENT STATION/Neville P. Clarke, Director! The Texas A81M University System/College Station, Texas Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Methods and Materials . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _i Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . if, Distribution and Abundance Patterns of Spiders Inhabiting Cotton in Texas D. A. Dean and W. L. Sterling Department of Entomology Texas A&M University Abstract Patterns of the distribution and abundance of spiders were determined in the major cotton growing areas of Texas during 1982-83. Misumenops spp., Oxyopes salticus Hentz, and Tetmgnatha laboriosa Hentz were among the most abundant taxa of spiders throughout the state. M isumenops spp. were most abundant in West and Northwest Texas, with M . celer (Hentz) the most common species in these areas. Oxyopes salticus was the most abundant spider in all areas of the state except West, Northwest, and South Texas but was abundant in these areas. T. laboriosa was predominant from East to South Texas. Because these species were found in all areas sampled, they are good candidates for detailed studies evaluating the impact of spiders on destructive ar- thropods in agroecosystems. The Texas Agricultural Experiment Station/Neville P. Clarke, Director/Texas A&M University System Introduction “In the development of science, empirically observed patterns almost always precede the discovery of causative principles that produce the patterns” (Ricklefs 1979). Thus, we need t0 know the patterns of distribution and abundance before the role of spiders can be determined. The role of spiders in cotton and other agroecosystems was reviewed by Riechert and Lockley (1984) but the role of most species is largely unknown (Nyffeler 1982). Spiders are predaceous on many species of insect pests; however, they also attack natural enemies of pests (Whit- comb and Bell 1964). Thus, it is largely unknown whether spiders contribute greater benefit by killing pest species, whether they are detrimental since they also feed on predators and parasites, or whether they are of little or no economic significance. Understanding the role of spiders in agroecosystems is crucial since spiders are one of the dominant arthropod groups in agroecosystems (Fuchs and Harding 1976). Even if the impact of spiders proves to be economically neutral, the ability to predict this neutrality is important since spiders could then be eliminated as an important factor in predicting the dynamics of other arthropods. The cotton fleahopper (Pseudatomoscelis seriatus [Reuter]) model (Hartstack and Sterling 1986) uses numbers of six spider species to predict fleahopper dynamics. The feeding ecology of Peucetia viridans (Hentz), Oxyopes salticus Hentz, and Argiope aurantia Lucas in a cotton field in East Texas was studied by Nyffeler et al. (1987a, b, c). Studies on other spider species in this cotton agroecosystem include Nyifeler et al. (1986, 1987d). Spiders are known to prey on various cotton insect pests as well as natural enemies. McDaniel and Sterling (1979, 1982) reported that Oxyopes salticus and Mis- umenops spp. fed on Heliothis virescens (F.) eggs. These two taxa of spiders also fed on small larvae of H . virescens (McDaniel et al. 1981). Oxyopes salticus has also been obsewed to eat P. seriatus (Kagan 1943, Whitcomb and Bell 1964). Misumenops spp. fed on Lygus (Whitcomb and Bell 1964), while M. celer (Hentz) fed on P. seriatus and Heliothis spp. larvae (Kagan 1943). Tetragnatha laboriosa Hentz was found to feed on P. seriatus (Kagan 1943) and Lygus lineolaris (Palisot de Beauvois) (Wheeler 1973). Bailey and Chada (1968) determined that O. salticus fed on most instars of H. zea (Boddie), which occur in sorghum fields. Spiders also feed on natural enemies in cotton and serve as food for other arthropods (Whitcomb and Bell 1964). The spiders found on cotton in the United States have been studied in several states: California (Leigh and Hunter 1969), Central (Kagan 1943) and East Texas (Dean et al. 1982), Arkansas (Whitcomb and Bell 1964), Missis- sippi (Lockley et al. 1979), Alabama (Skinner 1974), and South Carolina (Roach 1980). Only in Arkansas has the spider fauna been studies in all cotton gowing areas within the state. The objective of this study was to determine patterns in the distribution and abundance of common spiders in cotton fields in several areas of Texas. This survey was designed to indicate which spider species are suificiently abundant and widely distributed to play a major role inthe functioning of agroecosystems. Certain- 2 ly, the abundance of a spider species will not always relate to its importance as a natural enemy of some pest or beneficial species, since there are other factors such as ~ prey preferences and searching abilities that will affect itk)? efficiency Methods and Materials Cotton plants were sampled from 11 counties in Texas in 1982 and 23 counties in 1983 (including 10 of the 11 counties sampled in 1982). The cotton was either un- treated throughout the season or had not received any insecticide applications within about 3 weeks of sampling. Cotton was sampled in the major growing areas 1-3 times during the season. During part of 1982, 25 row samples, 1 meter (m) each, were taken in each field. For the remainder of 1982 and all of 1983, 10 row samples, 20 m each, were taken per field. Nearly 15,000 m of cotton rows were sampled in 80 fields during these 2 years. All sampling was done by D-Vac except for some sweeping or general searching, when time permitted, to collect adults or additional species. Abundance is based on D-Vac sampling only. Spiders were killed with carbon tetrach- loride and returned to the laboratory for storage in a freezer until identifications could be made. Voucher specimens are housed in the spider collection at Texas A&M University. Identification of species was based on adult specimens. Counties sampled in the different areas include: West Texas: Howard, Martin, Mitchell, Pecos, Reeves, and Tom Green. Northwest Texas: Crosby, Floyd, Gaines, Hale, Hock- ley, Lubbock, and Terry. North Texas: Collin, Delta, Hill, and Kaufman. Central Texas: Williamson. Southeast Texas: Fort Bend and Wharton. South Texas: Frio, Hidalgo, Nueces, and San Patricio. Collections from East Texas are from Walker County and cover the years 1978-81 using only D-Vac sampling for comparative purposes. The different areas shown in Figure 1 are based on the crop reporting districts in Texas Field Crop Statistics (Texas Department of Agriculture 1984). Results Cotton is grown in many areas of Texas and a total of 2.3 million hectares of cotton was planted in 1982 (Texas Department of Agriculture 1983) and 1.6 million hectares in 1983 (Texas Department of Agriculture 1984). In the samples taken during these years, emphasis was placed on the identification, distribution, and abundance of the more common species. Misumenops spp., Oxyopes salticus, and Tetragnatha laboriosa were the most abundant taxa of spiders throughout the state (Fig. 2). M isumenops spp. were most abundant in West and Northwest Texas. Misumenops celer was the numerically dominant M isumenops species in all areas of the state except South Texas where M. dubius (Keyserling) was more abundant. Oxyopes salticus was the most abundant spider in all areas of the state except West, Northwest, and South Texas. Tetragnatha L l laboriosa was most abundant in East and Southeast Texas Collin and N ueces Counties had the most species, i.e. and least abundant in West, Northwest, and Central 22 and 24, respectively, though more samples were taken ,_""\Texas. These three taxa of spiders comprised about 45 in these two counties. Only three genera of spiders A percent of total spiders in East and Southeast Texas; 64 contained more than three species each (Dictyna, Therid- percent in South Texas; 85 percent in Northwest Texas; ion, and Misunwnops Oxyopes salticus was found in all and about 75 percent in West, North, and Central Texas. counties sampled and Tetmgnatha laboriosa was found in g The highest density of spiders was in East and Central all but Crosby and Gaines Counties in Northwest Texas. Texas with 2.28 and 1.04/m, respectively (Fig. 2). A total of 6,948 spiders were collected by D-Vac during these 2 7‘ years. Oxyopes salticus is the most abundant spider on cotton in Texas (Dean et al.’ 1982), Arkansas (Whitcomb et al. 1963), Alabama (Skinner 1974), and South Carolina (Roach 1980). It is one of the most abundant in guar (Rogers and Horner 1977) and peanuts (Agnew et al. 1985) N W in Texas; alfalfa in Virginia (Howell and Pienkowski 1971); soybean in South Carolina (Roach 1980) and Iowa (Bechinski and Pedigo 1981); and sorghum in Oklahoma ‘z g (Bailey and Chada 1968). It is found throughout the ' O ' eastern halfof the United States and in the far west, but is O N g not reported from the Rocky Mountain region or the O O O . Great Basin, and is rarer in the northern states (Brady 1964). Oxyopes salticus appears to be an excellent colo- g ' ' nizer of cotton fields. The genus Misunwnops is the w second most abundant taxon on cotton in Texas. It is frequently included in lists of spiders of other crops as one of the more abundant spiders and is widely distributed throughout the United States and M. celer is common in L most of the United States but is rare in the northeast S ' (Kaston 1981). Tetragnatha laboriosa was more abundant a ‘ in East Texas than other areas and is usually listed as one of Areas Samp|ed the most abundant species in many crops: corn in Ohio 1 (Everly 1938); alfalfa in Kentucky (Culin and Yeargan ‘ 1983), New York (Wheeler 1973), and Virginia (Howell and Pienkowski 1971); and soybean in Illinois (LeSar and Unzicker 1978), Iowa (Bechinski and Pedigo 1981), and Kentucky (Culin and Yeargan 1983). Tetragnatha laborio- sa is found throughout North America (Levi 1981). Table 1 presents a list of the spider species and the counties in which they were collected. O. salticus was most abundant in Hill (0.77/m) and Collin Counties _ (0.57/m) in North Texas, and abundant in Williamson _ ,~.~~ _ . County (Central Texas) with 0.47/m. Misumenops spp. 1' -. ~: "- -‘-' ‘I were most abundant in Pecos (0.26/m) and Reeves ' _ l - (0.33/m) Counties in West Texas; Floyd (0.29/m) and Hale _ ' _ (0.31/m) Counties in Northwest Texas; and Williamson ' - - ". .. ". County (0.29/m) in Central Texas. Tetragnatha laboriosa ' ' " ' '- was more abundant in Southeast Texas (Fort Bend 0.12/m ,7. and Wharton 0.08/m), South Texas (Nueces 0.09/m), and North Texas (Collin 0.06/m) than in other areas. Dictyna spp. (found at all locations except Central and _ Southeast Texas) were more dominant in East (0.07/m), - ',_ ' West (Reeves 0.09/m, Tom Creen 0. 06/m), and Northwest ‘——-l_ (Floyd 0.05/m,= Hale 0.05/m) Texas than other areas. (Cgralmmgnzlage; tefcaréa (Bankszowgg/collecteg only iln North A¢fe3 Qf Cqflgn e ta . m ,' entra . m , an Sout Texas ' (Nueces 0.03/m). It also was present on cotton in Walker Planted In 1 ”\County in East Texas. Metaphidippus galathea (Walck- ‘ t ‘enaer) was most abundant in Central Texas (0.04/m) and ' Southeast Texas (Wharton 0.03/m). Theridion spp. were not found in West, Central, or Southeast Texas. Other species of spiders were either not abundant or only found in certain areas. Figure 1. Areas of cotton sampled and cotton acreage planted in Texas in 1983 (1 dot= 1,000 acres). Star in East Texas represents sampling from 1978-81. “HHJ x55: x51 mNd mxuEo U xxx mxozxzami E 56 @ 6:256 .0 E Em mmozwzamz g 6556 .2 a 6.535 .5 m Kim <25... E mnocim .0 E @652 m6“. mnd J<._.O._. F05 O8 3L m