Influence of Plant Frequency ations in the general food-plant complex may be important deter- and Certain Morphological Variations on Diets minants in the build-up or decrease of Melanoplus mexicanus popula- of Rangeland Grasshoppers tions. Mulkern et al. (1962) re- ported that grasshopper species with D. N. UECKERTI, R. M. HANSEN, AND C. TERWILLIGER, JR. high population densities in alfalfa Graduate Research Fellow and Professors of Range Science, Range Science fields ingested plant species in al- Department, Colorado State University, Fort Collins. most direct proportion to their abundance. Both the taxonomic Highlight composition and the physical struc- The frequency of plant species in the diets of 14 grasshopper species, col- ture of the vegetation have been lected on rangeland lightly grazed by cattle at the Eastern Colorado Range Sta- reported to be important environ- tion, was determined by microscopic examination of crop contents. Significant mental factors in determining the correlations were found between frequency of plant species in the habitat and the frequency of plant species in the diets of all grashopper species except distribution of grasshoppers (Can- Melanoplus confusus. No correlation was found between the body weight or &all, 1943; Isely, 1944; Isely, 1946; potential mobility of grasshopper species and the degree to which plant fre- Wolcott, 1937; Anderson, 1964; quency influences their diets. As the number of plant species eaten increased, Kaufmann, 1965). the influence of the relative availability of plant species on the diets decreased. There is a close correlation of There was no correlation between either body weight or potential mobility and the number of plant species eaten or the number of plant species/crop. the structure of mandibles and feeding habits in grasshoppers. Kaufmann (1965) indicated that Grasshoppers, which are gener- are attracted to those plants that grasshoppers with different feeding ally regarded as the most destruc- are nutritionally satisfactory be- habits have differently shaped tive . to range vegetation, com- cause the two organisms evolved to- maxillary lacinia and that mandi- monly damage range plants most gether, and that any strain that had bles can be classified as the gramini- severely when drought conditions a behavior pattern that caused it to vorous-type, the forb-feeding type, prevail, thus the effects of their feed on toxic plants or nutritionally and the moss-feeding type. feeding are severe (Stoddart. and deficient plants would be elimi- Comprehensive reviews of the Smith, 1955). Rangeland grasshop- nated. literature concerning the effects of pers differ widely in their feed- Size and mobility of may grasshoppers on rangeland and the ing habits, and the high degree affect feeding habits, food selection, food habits of grasshoppers have of selectivity in their feeding is well and energy flux. Mulkern, Ander- been prepared by Mulkern (1967), documented. Many theories have son, and Brusven (1962) observed Ueckert (1968a), and Mulkern et al. been presented in attempts to un- that the variety of food plants in- (1969). derstand the mechanism of food gested by grasshoppers increases Almost every year, millions of selection in grasshoppers. Mulkern, with morphologic development of dollars are spent on rangeland grass- Toczek, and Brusven (1964) re- the insect due to smaller crop ca- hopper control and forecasting of ported that the degree of selectivity, pacity and less mobility of the future population levels. If our that is the number of plant species younger instars. However, they ob- ultimate goal is understanding the eaten, is inherent in a grasshopper served no relationship between the ecology of rangeland and efficient species, but the expression of selec- adult size of a species and the num- control of pest species, then exact tivity is determined by the habitat. ber of plant species eaten. Langford knowledge of interrelationships, be- Leaves of different plants differ (1930) reported that adult female havior, and life histories is essen- relatively little in nutritional sub- Melanoplus bivittatus consume 2.5 tial. The purpose of this study was stances needed by insects and sub- times more forage than males of the to determine the influence of plant stances of no nutritional value, such same species. Male grasshoppers frequency, body weight, and poten- as glucosides, essential oils, alka- assimilate larger percentages of in- tial mobility upon the feeding loids, saponins, or tannins, act as gested food than females (Kauf- habits and diets of 14 grasshopper olfactory and contact chemical stim- mann, 1965). Larger body sizes in species common on sandhill range- uli which are effective at extraordi- insects result in increased food in- land in northeastern Colorado. narily low concentrations (Fraenkel, take (Reichle, 1968) and increased 1953; Dethier, 1954). Painter (1953) metabolic rate (Wiegert, 1965). Methods and Materials suggested that plant-feeding insects Various plant species have differ- ent effects upon survival, longevity, Study Area 1 Present address is Assistant Professor, fecundity, body size and propor- The study area was a 40.5 ha pas- Range and Wildlife Management De- tions, and rate of development. of ture on the Eastern Colorado Range partment, Texas Tech University, Scharff ( 1954) indi- Lubbock, Texas 79409. Received grasshoppers. Station, located 27 km north of March 5, 1971. cated that seasonal and yearly vari- Akron, in Washington County, 61 62 UECKERT ET AL

Colorado. The pasture had been Table 1. Plant frequency (%) on 1,000 40 x 40-cm plots on rangeland lightly lightly grazed by steers (4 ha/steer) grazed by cattle at Eastern Colorado Range Station, 1968. during the 5 summer months for 13 years prior to this study. The cli- Plants Frequency Plants Frequency mate of the area is semiarid with Grasses and grasslike plants Forbs (continued) an average annual precipitation of Agropyron smithii 17.1 Euphorbia spp. 0.2 about 38 cm, most of which comes Andropogon hallii 3.8 Evolvulus nuttallianus 1.6 as rain during the growing season. Aristida longiseta 0.7 Gaura coccinea 0.7 The frost-free season usually starts Bouteloua gracilisl 64.9 Haplopappus spinulosus 0.2 in May and lasts until early Octo- Calamouilfa longifolia 70.3 Hoffmannseggia jamesii 0.1 ber. This study was restricted to Festuca octof lora 38.0 Ipomoea leptophylla 0.3 the “deep sand” range sites where Hordeum ju ba turn 0.6 Lepidium densiflorum 4.2 soil textures are sandy loam and Sporobolus cryptandrus 3.9 Lesquerella ludoviciana 0.1 loamy sand, and the topography is Stipa comata 60.9 Lia tris puncta ta 0.4 Carex heliophila dune type with no definite drain- 11.1 Lithospermum incisum 1.1 Lupinus pussilus 0.1 age patterns. Lygodesmia juncea 0.1 The study area is in a Bouteloua- Forbs Opun tia humifusa 2.0 Calamouilfa-Stipa-Artemisia asso- Ambrosia psilostachya 32.6 Penstemon albidus 0.3 ciation in the mixed-grass prairie in Artemisia filifolia 10.3 Phlox spp. 1.0 which grasses make up about 80% Artemisia ludoviciana 5.4 Physalis subglabrata 0.2 of the total dry weight of above- Asclepias pumila 2.7 Plan tago purshii 0.6 ground vegetation. The major Astragalus spp. 1.0 Psoralea lanceolata 1.7 grasses and their contribution to Chenopodium album 18.4 Psoralea tenuiflora 5.1 total herbage production include Cirsium undulatum 1.9 Sphaeralcea coccinea 5.4 blue grama (Bouteloua grucilis), Croton texensis 0.1 Thelesperma megapotamicum 5.2 Tradescantia occidentalis 42%; prairie sandreed (Calamovilfa C yptan tha sp. 0.5 3.4 Eriogonum annum 0.9 Yucca glauca 0.1 Zongifolia), 18%; and needleand- thread (St+ corn&a), 16%. Other 1 Frequency for Bouteloua gracilis was recorded on a 5 X 5-m plot. important grasses include sand dropseed (Sporobolus cryptandrus), quency of the plant species on the western wheatgrass (Agrofiyron grasshoppers were collected bi- study area and the percent fre- smithii), and sand bluestem (Andro- weekly during the 1968 growing Specimens were captured quency of the plant species in the pogon hallii). Sand sagebrush season. diet of each grasshopper species to (Artemisia filifolia) is the only im- with sweep nets or by hand from determine the degree to which diets portant shrub on the study area. the study area. Captured specimens are influenced by plant frequency. Forbs make up about 6% of the were killed immediately in 95% A correlation coefficient was calcu- total dry weight of above-ground ethanol and stored in the alcohol lated between the diet-plant fre- plant biomass. Common forbs in- until laboratory work was begun. quency correlation coefficients for clude western ragweed (Ambrosia Several specimens of each species all grasshopper species and the psilostachya), scarlet globemallow were saved as reference specimens number of plant species eaten to (Sphaerulcea coccinea), lambsquar- for identification. An ocular esti- determine the influence of dietary ters (Chenopodium album), and mate of the density of grasshopper selectivity upon the degree to which scurfpea (Psoralea spp.). populations was made during each diets are influenced by plant fre- The frequency of plant species collection period. quency. on the study area was recorded on A microscope slide was prepared Femur and tegmen lengths and 1000 quadrats on l-3 July 1968, by from the contents of each individ- body weights were determined on a “nested quadrat” technique ual grasshopper crop, and the com- 21 to 46 specimens of each sex for (Hyder et al., 1965). The frequency position of diets was estimated by 11 grasshopper species. An approxi- for blue grama was recorded on a examining the slides under a micro- mate live weight was obtained on 5 x 5-cm quadrat and a 40 x 40-cm scope as described by Ueckert individual specimens by air-drying quadrat was used for all other spe- (1968b). Plant tissues on slides were the alcohol-preserved specimens for cies. We assumed that plant fre- identified by comparison with ref- quency in this plant association erence tissue of identified plants. about 2 hours at room temperature would not change appreciably dur- Twenty fields/slide were examined and then weighing them. The mo- ing the growing season. and frequency percentages were bility of each grasshopper species calculated for each food item studied was assumed to be propor- Grasshopper Diets present. tional to its mean femur and teg- About 50 adult specimens of each Correlation coefficients were cal- men lengths. Correlation coeffi- of the most numerous species of culated between the percent fre- cients were calculated between RANGELAND GRASSHOPPER DIETS means of each of these three mea- Table 2. Frequency (96) of plant species in the diets of 14 grasshopper species surements and (1) the total number common on sandhill rangeland in northeastern Colorado. of different plant species eaten by each grasshopper species, and (2) Grasshopper species1 the mean number of plant species/ Plant species 1 2 3 4567 8 9 10 11 12 13 14 crop for each grasshopper species, Agropyron smithii 12 3 28 21 17 1 4 7 4 6 26 28 1 32 to determine the correlation be- Andropogon hallii