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 insect. 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 insects 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 Arphia conspersa, 4-Arphia pseudonietana, 5-Cordillacris occipitalis, 6- Eritettix simplex, 7-Melanoplus angustipennis, 0-Melanoplus confusus, 9-Melano- of grasshoppers on the study area plus foedus, IO-Mermiria maculipennis, 1 I-Pardalophora apiculata, 12-Spharagemon increased from about 2/m2 in early collare, 13-Trachyrhachys kiowa, and 14-Xanthippus corallipes. May to about 20/m2 in mid-June and remained near this level except Melanoplus confusus (Table tegmina from 1.0 to 1.3 times longer throughout the summer. The num- 3). Plant frequency in the habitat than males of their respective spe- ber of specimens of each species accounted for as much as 74% (r2 = cies. Mean grasshopper weights analyzed does not represent its rela- 0.74) of the variability of plant fre- varied from 184 mg for Eritettix tive abundance. quency in the diets of Eritettix sim- simplex to 1,420 mg for Pardalo- Correlation coefficients between plex and Mermiria maculipennis, phora apiculata while femur and the percent frequency of plant spe- and for as little as 21% (r-2 = 0.21) tegmen lengths varied from 1.12 cies in the diet and the percent fre- of the variability of plant frequency cm and 1.27 cm respectively for quency of plant species in the habi- in the diet of Melanofks foedus. Ageneotettix deorum to 1.93 cm tat were positive and significant (P Females were from 1.2 to 3.6 and 3.43 cm respectively for P. = 0.01) for all grasshopper species times heavier and had femora and apiculata (Table 4). 64 UECKERT ET AL.
Table 3. Correlation of the frequency Table 4. Number of plant species eaten, mean number of plant species/crop, (%) of plant species in the diets of mean femur and tegmen lengths (cm), approximate mean live weights (mg), 14 species of grasshoppers with the and number of crops examined from grasshoppers collected at Eastern Colo- frequency (%) of plant species in rado Range Station, 1968. their habitat at Eastern Colorado Range Station. Plant Mean no. Total species plant Mean1 Mean1 Mean1 no. Species l-1 Grasshopper species eaten species/crop femur tegmen weight crops
Eritettix simplex +0.86 Ageneotettix deorum 12 1.9 1.12 1.27 187 250 Mermiria maculipennis +0.86 Amphitornus coloradus 6 1.2 1.28 1.70 212 97 Ageneo tettix deorum +O.Sl Arphia conspersa 11 1.6 1.35 2.46 514 191 Cordillacris occipitalis +0.74 Arphia pseudonietana 9 1.5 1.58 2.77 678 151 Arphia conspersa +0.67 Cordillacris occipitalis 6 1.2 90 Xanthippus corallipes +0.65 Eritettix simplex 10 1.5 1.14 1.39 184 146 Amphitornus coloradus +0.62 Melanoplus angustipennis 38 3.0 1.19 1.64 210 227 Trachyrhachys kiowa +0.57 Melanoplus confusus 24 1.9 106 Arphia pseudonietana +0.56 Melanoplus foedus 34 2.7 1.48 2.16 480 151 Pardalophora apiculata +0.52 Mermiria maculipennis 6 1.1 84 Melanoplus angustipennis +0.52 Pardalophora apiculata 13 2.1 1.93 3.43 1420 110 Spharagemon collare +0.51 Spharagemon collare 19 2.1 1.47 2.53 525 144 Melanoplus foedus +0.45 Trachyrhachys Kiowa 6 1.2 1.19 1.95 223 200 Melanoplus confusus +0.042 Xanthippus corallipes 14 1.9 1.82 3.33 1378 226
1 All correlation coefficients are significant l Average of male and female means. at the 1% level of significance except for Melanoplus confusus. 2 Not significant at the 5% level of signifi- by the grasshopper species studied the lower correlation coefficients cance. (P = 0.05). may not be ecologically important, this study provides evidence that Discussion the diets of grasshoppers are influ- The number of plant species Although all herbivores have enced by the plant composition in eaten varied from 6 to 38 in the food preferences, it is only logical the habitat, even though strong grasshopper species studied. Amphi- to expect that plant frequency in feeding preferences are expressed. tornus coloradus, Cordillacris occi- their habitat exerts some degree of The influence of plant frequency pitalis, Mermiria maculipennis, and influence upon their food habits. upon feeding habits varies among Trachyrhachys Kiowa each fed on The frequency of a species of plant grasshopper species. There was no six plant species while Melanoplus in the habitat determines how often correlation between the body weight angustipennis fed on 38 plant spe- a herbivore will encounter it as it or potential mobility of grasshop- cies (Table 4). The mean number moves about. Similarly, the percent per species and the degree to which of plant species/crop varied from of the total biomass of live, above- plant frequency influences diets. 1.1 in M. maculipennis to 3.0 in M. ground vegetation that a plant spe- The food preferences of a grasshop- angustipennis. cies comprises determines its rela- per species are apparently genetic- Correlation coefficients of femur tive availability as a potential food ally inherited traits and are not dic- lengths, tegmen lengths, and body for herbivores. tated by the grasshopper’s ability weights of 11 grasshopper species A non-selective feeder could be to search for foods. However, a and the number of plant species expected to eat foods exactly in pro- negative correlation was found be- eaten were not significant (P = portion to the frequency with which tween the number of plant species 0.05). Correlation coefficients of they were encountered, and conse- eaten by the grasshopper species the same three body measurements quently, 100% of the variability in studied and the influence of plant of the 11 species and the mean num- its diet would be associated with frequency upon their diets. As ber of plant species/crop were not plant frequency. In this study feeding selectivity decreased (or the significant (P = 0.05). Correlation there was statistically significant number of plant species eaten in- coefficients of femur lengths, teg- correlation between the frequency creased) the influence of the rela- men lengths, and body weights of of plants in the habitat and the fre- tive availability of plant species on the 11 species and their diet-plant quency of plants in the diets of all the diet decreased, thus diets of spe- frequency correlation coefficients grasshopper species except M. con- cies which feed on few different were not significant (P = 0.05). fusus. As much as 74% of the vari- plant species (stenophagous) are There was a negative correlation ability in the diets of E. simplex generally influenced more by plant (r = -0.55) between diet-plant fre- and M. maculipennis may be as- frequency than are diets of species quency correlation coefficients and sociated with plant frequency in which feed on many different plant the number of plant species eaten their habitat. Although some of species (euryphagous). RANGELAND GRASSHOPPER DIETS 65
The number of plant species in 119. In Principles of Plant and ani- habits and preferences of grassland the diet of a herbivore is an index mal pest control, Vol. 2 weed control. grasshoppers of the north central of selectivity; stenophagous herbi- Pub. 1597. Nat. Acad. of Sci., Wash- great plains. North Dakota Agr. Exp. Sta. Bull. No. 481. 32 p. vores are more selective, whereas ington, D. C. 471 p. DETHIER, V. G. 1954. Evolution of MULKERN, G. B., D. R. TOCZEK, AND euryphagous species are more gen- feeding preferences in phytopha- M. A. BRUSVEN. 1964. Biology and eral feeders. It would seem that gous insects. Evolution 8:33-54. ecology of North Dakota grasshop- euryphagous species should be able FRAENKEL, G. 1953. The nutritional pers. II. Food habits and prefer- to adapt to more niches than ste- value of green plants for insects. ences of grasshoppers associated with nophagous species, and thus be fav- Ninth Int. Congr. Entomol., Trans. the sand hills prairie. North Dakota ored by evolutionary selection. 2:90-100. Agr. Exp. Sta. Res. Rep. No. 11. However, specialization (in diet or HYDER, D. N., R. E. BEMENT, E. E. 59 p. otherwise) is generally considered REMMENCA,AND C. TERWILLIGER, JR. PAINTER, R. H. 1953. The role of nu- to be a deepening rut in evolution 1965. Frequency sampling of blue tritional factors in host plant selec- (National Academy of Sciences, grama range. J. Range Manage. 18: tion. Ninth Int. Congr. Entomol., 90-94. Trans. 2: 101-105. 1968). ISELY, F. B. 1944. Correlation between REICHLE, D. E. 1968. Relation of body There was no correlation between mandibular morphology and food size to food intake, oxygen consump- body weight or potential mobility specificity in grasshoppers. Entomol. tion, and trace element metabolism of the grasshopper species stuclied Sot. Amer., Ann. 37:47-67. in forest floor arthropods. Ecology and the number of plant species ISELY, F. B. 1946. Differential feed- 49:538-542. eaten or the number of plant spe- ing in relation to local distribution SCHARFF,D. K. 1954. The role of food cies in their crops while grazing un- of grasshoppers. Ecology 27: 128-138. plants and weather in the ecology of der natural conditions. Large grass- KAUFMANN,T. 1965. Biological stud- Melanoplus mexicanus mexicanus hoppers are not more highly ies on some Bavarian Acridoidea (Sauss.). J. Econ. Entomol. 47:485- selective nor less selective than (Orthoptera), with special reference 489. smaller, less mobile species. Larger to their feeding habits. Entomol. STODDART,L. A., ANDA. D. SMITH. 1955. Sot. Amer., Ann. 58:791-801. species do not move from plant to Range management. McGraw-Hill LANGFORD,G. S. 1930. Some factors Book Co. Inc., New York. 433 p. plant while feeding any more than relating to the feeding habits of grass- UECKERT, D. N. 1968a. Diets of some smaller and less mobile species. hoppers with special reference to grasshoppers common on mountain Melanoplus bivattatus. Colorado herbland in northern Colorado. M.S. Literature Cited Agr. Exp. Sta. Bull. 354. 53 p. Thesis. Colorado State Univ. Fort ANDERSON,N. L. 1964. Some relation- MULKERN, G. B. 1967. Food selection Collins, Colorado. 43 p. ships between grasshoppers and vege- by grasshoppers. Ann. Rev. Ento- UECKERT, D. N. 196813. Seasonal dry tation. Entomol. Sot. Amer., Ann. mol. 12:59-78. weight composition in grasshopper 57: 736-742. MULKERN, G. B., J. F. ANDERSON,AND diets on Colorado herbland. Ento- CANTRALL,I. J. 1943. The ecology of M. A. BRUSVEN. 1962. Biology and mol. Sot. Amer., Ann. 61:1539-1544. the Orthoptera and Dermaptera of ecology of North Dakota grasshop- WIEGERT, R. G. 1965. Energy dynamics the George Reserve, Michigan. Mus. pers. I. Food habits and preferences of the grasshopper populations in Zool. Univ. Michigan, Misc. Pub. of grasshoppers associated with al- old field and alfalfa field ecosystems. 54: l-182. falfa fields. North Dakota Agr. Exp. Oikos 16: 161-176. NATIONALACADEMY OF SCIENCES,COM- Sta. Res. Rep. No. 7. 25 p. WOLCOTT, G. N. 1937. An animal cen- MITTEE ON PLANT ANDANIMAL PESTS, MULKERN,G. B., K. P. PRUESS,H. KNUT- sus of two pastures and a meadow SUBCOMMITTEEON WEEDS. 1968. The SON, A. F. HAGEN, J. B. CAMPBELL, in northern New York. Ecol. Mon- biological control of weeds, p. 86- AND J. D. LAMBLEY. 1969. Food ogr. 7: l-90.
1972 Annual Meeting February 5-11 Washington, D. C. 1972 Dues Information concerning the program, special events, Society dues, which include an annual subscription and accommodations were presented in the November to the Journal of Range Management and Rangeman’s 1971 Journal of Range Management and the Decem- News, are on a calendar year basis. Dues for 1972 were ber 1971 Rangeman’s News. payable on or before January 1; if you have not yet Preregistration is open until January 31. Please renewed for the current year, you are urged to do so contact the Executive Secretary, 2120 South Birch Street, Denver, Colorado 80222 for additional infor- as soon as possible. mation.