Light to moderate popuhtions (50-200 per m2) of black grass bugs in a seeded monoculture of crested wheatgrass appeared to reduce plant vigor. Vigor of ungrazed plants was compared to plants gazed only by black grass bugs and plants grazed by black grass bugs and cattle. Generally, vigor decreased as levels of grazing increased. Leaf length, seedhead height, root crown nonstructural carbohydrates, and plant color correlated positively with vigor while functions of axillary tillering such as basal area and seedhead density correlated negatively with vigor. Cattle grazing was not in excess of intensities recognized as proper for the area. Black grass bugs (Labops hesperius Uhler) are an important factor in some intermountain area rangeland ecosystems(Bohning and Currier 1967, Todd and Kamm 1974, Haws 1978). Apparently the insect is native to the West, having been sighted in some western states as early as 1870. However, since the acreage of seeded, largely monocultural wheatgrass (Agropyron sp.) stands has increased, the insects have expanded greatly in number and range (Bohning and Currier 1967, Jensen 1971). Areas seeded to grass provide an optimum habitat for the insect because food is abundant and reproductive conditions are favorable, while natural predators such as spiders find the grass monoculture generally unsuitable. The life cycle of the black grass bug begins usually in late March after snow melt and lasts about 3 months. Only one generation is produced per year and the insects overwinter as eggs (Todd and Kamm 1974). Greatest feeding intensity occurs during the adult stage which lasts from late April to the end of June (Bowers 1976). The black grass bug appears to favor cool-season grasses such as crested wheatgrass (Agropyron cristatum) when feeding and damages plant tissue by piercing cell walls of leaves and stems and removing intercellular liquids (Haws 1978). The effect of the insect on photosynthetic capacity could be significant because of this feeding characteristic. Jensen (1971) noted that the insect can give wheatgrass fields a straw colored appearance during critical spring growth periods. Moderate to heavy populations of black grass bugs (100 -Iper m*) have also reduced total dry weight production, digestibility, nutritional value, and palatability (Bohning and Currier 1967, Todd and Kamm 1974, Higgins et al. 1977). Lower populations (less than 100 per mz) did not significantly affect dry herbage yield or digestibility (Malechek et al. 1977). Herbage production, digestibility, nutritional value, and palatability all reflect forage value of the plant but may not be the best indices for determining plant vigor (Mueggler 1975, Cook 1977). This study measured effects of black grass bugs on crested wheatgrass characteristics such as vertical and lateral growth, density of growth, plant color, carbohydrate reserves, and phenology which may provide an indication of how the insect affects plant vigor. A Authors are graduate research assistant, Plant Science Division, University of Wyoming, Laramie 82071, formerly a graduate researchassistant, Range Dept., Utah State University, Logan 84322 McKell is a former USU profes,sor and is presently working for Native Plants 1°C:. 360 Wakara Way, Salt Lake City, Utah 84108. Grateful acknowledgement IS extended to Dr. Austin Haws, who provided assistancc in making these field plots available for study. This study was supported by Exp. Sta. Project No. 823 and by a grant from the Four Corners Regional Commission. Manuscript received December 29, 1980. reduction in vigor could ultimately affect community characteristics such as trend, condition, and grazing capacity (Cook 1977). Materials and Methods The study was conducted from September 1976 to May 1978 on the Sterling Ranch in Diamond Fork Canyon, located east of Spanish Fork, Utah. The elevation and annual precipitation are 1700 m and 40 cm, respectively. The study area was seeded to a monoculture of crested wheatgrass in 1965. The experimental design consisted of three different treatments: ungrazed control, insect-grazed, and insect/livestock-grazed. The ungrazed treatment consisted of five fenced exclosures (constructed by the U.S. Forest Service in December, 1974) (each 25 m*) treated each spring with Temik, a granual systemic insecticide (C~HI~N~OZS), at the rate of 187.5 g/.25 n¶* (Union Carbide Corp. 1975). The insect-grazed treatment consisted of five fenced exclosures without Temik treatment. Five unfenced areas (each 25 m*) on open rangeland represented the insect/livestock-grazed treatment. Strips of sheet metal 30 cm high were attached to the base of the fenced exclosures to keep rodents out of the exclosures. However, it was noticed that the rate of snow melt in the spring was reduced in areas adjacent to the metal strips. This increased moisture availability for plants growing near the fence. Therefore, all sampling was done at least one meter away from the fence. Vertical and lateral growth were measured in terms of leaf length (cm), seedhead height (cm), basal area (cm*), and density of growth. Leaf length and seedhead height were measured at 2-week intervals during the fall of 1976 and spring through fall of 1977. Six plants were chosen at random in each exclosure each time leaf length and seedhead height were measured. Leaf length and seedhead height were measured from the root crown to the tip of the longest leaf and tip of the highest seedhead respectively. Leaves were straightened to their full length when measured. Only one leaf and seedhead were measured per plant. Basal areas of the plants were measured once in the spring of 1978. Six plants were chosen at random in each exclosureformeasurement. Density ofgrowth was estimated by measuring seedhead quantities per plant. Seedhead density was measured once in the summer of 1977 after seedheads for all plants in all treatments were fully developed. Six measurements per exclosure were taken. Crested wheatgrass root crown nonstructural carbohydrates (RCNC) were measured as an indication of reserve sugar levels because they are the main storage site of nonstructural carbohydrates in this species and are subject to the least amount of short term variation (White 1973). Root crown tissue was collected from live plants, washed free of soil in cold water, and maintained in 85% ethanol until analysis. The samples were oven dried at 500 C for 48 hours and ground in a Pika mill to a fine powder. Crested wheatgrass stores RCNC in the form of short chain fructosans which undergo nearly 100% hydrolysis in a mild acid (Smith 1969). Therefore, 0.5 g samples (5 samples per exclosure) were refluxed in 50 ml 0.2 N sulfuric acid at IOO-105°C for 1 hour to separate RCNC from structural material (Smith et al. 1964). Samples were 586 JOURNAL OF RANGE MANAGEMENT 35(5), September 1982 filtered (Whatman No. 2). neutralized with 2 ml 30% NaOH and brought to a final volume of 100 ml with HzO. 1 ml of sample solution was added to 2 ml dinitrosalicyclic acid reagent and boiled in a water bath 15 minutes. After cooling, samples were diluted with 5 ml HsO. Within 1-2 hours after boiling, color intensities were measured with a Beckman Model DU Spectrophotometer at 540 mu and compared to glucose standards. Values were reported in milligrams RCNC per gram dry weight of root crown material. The acid reagent was prepared by dissolving (with warming) 5 g 3,5-dinitrosalicyclic acid in 100 ml 2N NaOH. This solution was mixed with a 60 percent potassium-sodium tartrate solution (prepared by dissolving 150 g in 250 ml Hz0 with warming). Hz0 was added to make a final volume of 500 ml. The phenology of crested wheatgrass and the stages of the black grass bug life cycle were recorded at 2-week intervals from spring to fall. Plant color, a general indicator of photosynthetic activity, was estimated by visual observation during late summer and fall. Color was ranked according to the percentage of the whole plant which appeared green. Rankings were O-25, 25-50,50-75, and 75-100% green. Leaf length, seeded height, basal area, density of growth, RCNC reserves and plant color were evaluated statistically by analysis of variance (completely randomized design with subsampling). Comparisons of treatment means at each sampling date were accomplished by Duncan’s Mean Comparison test (Steel and Torrie 1980). Black grass bug population densities outside the exclosures averaged between 50 to 100 bugs per m* in the spring of 1977. One of two black grass bugs per meter* were found in the Temik treated exclosures. Black grass bugs were observed to be the predominant insect at the site. No insect population data were taken in 1976. However, Browsers (1976) found 200 black grass bugs per rnr in early June 1975 and Malechek et al. (1977) found between 30 and 156 insects per rnz in early June 1974. Cattle grazing at the ranch was managed by the U.S. Forest Service from 1965 to 1977. Grazing data are shown in Table 1. Herbage production at Sterling Ranch is about 1700 kg/ ha (1500 lb/acre) annually (Malechek et al. 1977). Proper use (33% total production) is therefore 560 kg/ ha or, about 1.54 AUM perhectare (assuming one AUM requires 363 kg air dry forage). Proper use was exceeded only 1969 (Table 1). Table 1. Cattle grazb~g intensities at Sterling Ranch’ from 1966 to 1978. AUM Grazing Use Year level (AUM ha-‘) Grazing duration 1966 0 0 Pasture was rested 1967 111 .65 June 6-June 25 1968 83 .49 June 6-June 25 1969 577 3.39 June 6-July 1 1970 253 1.49 June g-June 2