Wyoming distribution map
The fourspotted grasshopper has a wide distribution in western grasslands. It inhabits the shortgrass, mixedgrass, desert, and bunchgrass prairies. It prefers to feed on blue grama and is commonly found where this and other shortgrasses are the dominant vegetation. In the mixedgrass prairie where mid grasses and short grasses grow in mosaic patches, the fourspotted grasshopper occupies the patches of short grass. It has been recorded infrequently from the tallgrass prairie but with no description of the specific habitat in which it occurs.
The fourspotted grasshopper is a medium-sized rangeland species. Average live weights of males from the mixedgrass prairie of eastern Wyoming average 110 mg; females are much larger weighing an average 300 mg (dry weight: males 35 mg, females 90 mg).
Individual grasshoppers in the field, however, may contain a substantial amount of other grasses. For example, one female inhabiting the shortgrass prairie of Colorado had 40 percent western wheatgrass in its crop contents while another had 43 percent buffalograss. In addition to grasses, a few grasshopper crops have been found to contain small amounts of two sedges (needleleaf sedge and threadleaf sedge) and five species of forbs (prairie onion, fringed sagebrush, hairy goldaster, spreading fleabane, and scarlet globemallow).
The fourspotted grasshopper selects green leaves for its food. This species has not been observed to feed on dry plant litter in its natural habitat. Tests of caged grasshoppers indicated that only 6 percent of the insects had fed on bran bait.
Several observations of the feeding of this grasshopper in the mixedgrass prairie of eastern Wyoming indicate that it attacks grass in two chief ways. A grasshopper may climb up a green leaf of blue grama, turn around and feed about 1 inch from the tip, and proceed toward the base, ingesting the whole width and hanging onto adjacent leaves. The end pieces are cut off and fall. The second method is for a grasshopper sitting in a horizontal or diagonal position on the plant to begin feeding on the end of a leaf and progress toward the base.
Little is known about its dispersal and migration. Where the bigheaded grasshopper, A. elliotti, has often appeared as accidentals in the mountains west of Boulder, Colorado, no fourspotted grasshopper has ever been found there. However, evidence that the species occasionally disperses comes from a mixedgrass prairie of eastern Wyoming in which this grasshopper occurred at a density of 7 nymphs per square yard. An area of 840 acres was sprayed in 1970 with an insecticide resulting in the virtual elimination of this species. Not until 1973 was the species found again when one female was encountered in 100 square-foot samples. The following year two nymphs were found in 100 square-foot samples. The population evidently gained a new foothold in the area from dispersing adults and began once more to increase.
The nymphs are identifiable by their shape, external structures, color, and color patterns (Fig. 1-5).
1. Head is relatively large, face moderately slanting; antennae filiform. Instar I with dark brown vertical stripe below compound eye and with dark brown horizontal band behind compound eye that extends onto lateral lobe of pronotum, background color of head ivory. Postgena of head and anteroventral region of lateral lobe colored dark brown forming a vertical band that runs nearly parallel with the dark vertical band below compound eye. Instars II to V background color of head mainly green, dark brown band below compound eye becomes faded and broken; a vertical ivory band below compound eye is evident.
2. Pronotum with lateral carinae ivory-colored and constricted in central region (Fig. 8), constriction increases as nymphs molt from one instar to the next. Pronotal lobe with diagonal ivory ridge on anterior central region.
3. Hind femur with medial area almost entirely fuscous in instars I to III, partly green in instar IV and V. Hind tibia tan and gray or pink in late instars.
4. General color pattern of instar I ivory with fuscous band extending from behind compound eye to end of abdomen; instars II to V green or occasionally tan, the fuscous band entire on side of head and abdomen, broken on lobe of pronotum.
In western South Dakota, females have been observed to oviposit into soil next to buffalograss at maximum depths of 1 inch. The eggs are laid in clutches of 6 to 14 eggs and are contained in a tough pod seven-eighths to one inch long (Fig. 10). The eggs are tan and 4.8 to 5.2 mm long. The eggs pass the winter in the soil, but no study has been made of their embryology. The species has one generation annually.
Densities of fourspotted grasshoppers, when subdominant in grasshopper assemblages, usually range from 0.2 to 1.5 young adults per square yard. When the species is dominant, densities may be as great as five per square yard. No information is available on how rapidly and under what conditions populations of this grasshopper rise to high densities and dominance.
In a population inhabiting the mixedgrass prairie of eastern Wyoming, the fourspotted grasshopper persisted for at least eight years at fluctuating, low densities. Densities of this species and the entire assemblage are shown for five years in Table 1.
A potentially significant mortality factor of fourspotted grasshoppers is parasitism by dipterous larvae. In populations of this species on the shortgrass prairie of northcentral Colorado, 12 percent of adults have been found to be parasitized by flesh fly larvae. Of these larvae, 64 percent were killed by the host and melanized, thereby reducing the negative impact of the parasite on population growth of the host.
Anderson, N. L. 1973. The vegetation of rangeland sites associated with some grasshopper studies in Montana. Montana Agr. Exp. Stn. Bull. 668.
Hewitt, G. B. and J. A. Onsager. 1982. A method for forecasting potential losses from grasshopper feeding on northern mixed prairie forages. J. Range Management 35: 53-57.
Larsen, J. C., J. A. Hutchason, and T. McNary. 1988. The Wyoming Grasshopper Information System. Cooperative Agricultural Pest Survey, University of Wyoming, Laramie.
Mulkern, G. B., K. P. Pruess, H. Knutson, A. F. Hagen, J. B. Campbell, and J. D. Lambley. 1969. Food habits and preferences of grassland grasshoppers of the North Central Great Plains. North Dakota Agr. Exp. Stn. Bull. 481.
Otte, D. 1970. A comparative study of communicative behavior in grasshoppers. Univ. Michigan Mus. Zool. Misc. Publ. 141.
Pfadt, R. E. and R. J. Lavigne. 1982. Food habits of grasshoppers inhabiting the Pawnee site. Wyoming Agr. Exp. Stn. Sci. Monogr. 42.
Pooler, P. D. 1989. Factors influencing grasshopper oviposition site selection on South Dakota rangelands. M.S. thesis, South Dakota State University, Brookings, SD.
Przybyszewski, J. and J. L. Capinera. 1991. Patterns of parasitism among shortgrass prairie grasshopper (Orthoptera: Acrididae) populations. J. Kansas Entomol. Soc. 64: 5-17.
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