Wyoming distribution map
The bluelegged grasshopper, a large bandwinged species, has a wide geographic range in western North America. It inhabits the shortgrass, mixedgrass, bunchgrass, desert, and tallgrass prairies. In the northern mixedgrass prairie, where populations reach their highest densities, the species prefers to live in areas dominated by western wheatgrass. These are mesic habitats commonly occurring on clay soil flats, in valley bottoms, and in old dry lake beds. The close plant-insect relationship is probably the main reason for a patchy distribution of this grasshopper.
The damage is usually done in participation with other rangeland species, often with the bigheaded grasshopper, Aulocara elliotti, or the whitecrossed grasshopper, Aulocara femoratum. The densities of the bluelegged grasshopper in assemblages occupying its preferred habitats usually range from one to four adults per square yard, but in some situations densities may reach ten per square yard.
The bluelegged grasshopper is a large species. Live weights of males from northern mixedgrass prairie average 294 mg and of females 828 mg (dry weights: males 97 mg, females 236 mg).
The method of attacking a host plant by this grasshopper is unusual. Crawling on the ground, a hungry adult contacts a host plant such as western wheatgrass or needleandthread, climbs the plant, and cuts a 3 to 4 inch terminal section of leaf, which falls to the ground. The grasshopper immediately drops to the ground and recovers the cut section. Handling the cut terminal with its front tarsi, the grasshopper devours it from one end to the other. While searching for food, a hungry grasshopper may instead contact a green section of leaf lying on the ground or an attached recumbent leaf and feed on it. The method of attack used by instars II to V is similar to the adults; they climb and cut terminal sections of leaves and feed on them from a horizontal position on the ground or they feed on ground litter, both green and dry grass leaves. No observations of feeding of instar I have been made.
Evasive flights begin about 8:30 a.m. DST on clear days when soil temperatures have risen above 60°F. These flights are straight and 6 to 12 inches high, the adults softly crepitating and travelling distances of 3 to 15 feet.
Although no direct observations of group migratory flights have been made, circumstantial evidence indicates that such behavior occurs. In eastern Wyoming a preferred habitat dominated by western wheatgrass became drought stricken in July 1989, and the usually luxuriant grasses stopped growing and turned brown. Where both the bigheaded grasshopper and the bluelegged grasshopper occurred in economic densities on 1 July 1989, only the bigheaded grasshopper remained at high densities 20 July 1989. The bluelegged grasshopper had disappeared and presumably emigrated to more favorable habitats that had received spotty rainfall during the summer. Two possible stimuli for the emigration of the bluelegged grasshopper were the exhaustion of its preferred food plants and the deterioration of the microhabitat. On the other hand, the bigheaded grasshopper, with less stringent ecological requirements, chose to remain in the deteriorating habitat.
The nymphs are identifiable by their shape, structures, and color patterns (Fig. 1-5).
1. Head: face nearly vertical, a diagnostic light band beginning from near top of compound eye and running diagonally backwards on the occiput, the band from one eye converges on the other but the bands do not meet, bands sometimes faint. Figures 1-5 show side view of left band beginning above compound eye and running diagonally on occiput.
2. Pronotum with disk wrinkled; median carina distinct and elevated higher on the prozona than the metazona, cut twice, in front of middle and near middle; lateral lobe with posteroventral angle acute and drawn downward.
3. Hind femur with sparse hairs on lower carina; this characteristic separates bluelegged nymphs from Kiowa grasshopper nymphs (Trachyrhachys kiowa), which possess a thick fringe of hairs on the lower carina. Color of hind tibia of instars I and II is fuscous, of instars III and IV fuscous and gray, of instar V pale blue or pale blue, tan, and fuscous.
4. General body color tan to brown with many dark brown maculations imparting a dark brown aspect to all instars.
Observations have not been made of the courting and mating behavior of this grasshopper, but several observations of oviposition in northern mixedgrass prairie have been made. A gravid female ready to lay selects either bare ground or ground covered by litter among shortgrass, if available, and works her ovipositor 2 inches deep into the soil. The time taken to begin and end oviposition has not been observed, but one female with her ovipositor already inserted took 32 minutes until withdrawal. A female covers the hole by tamping with her hindlegs and brushing with her ovipositor. A clutch consists of 14 large reddish brown eggs measuring 6.3 to 7.3 mm in length (Fig. 10). There is one generation annually.
A biological control factor affecting populations of the bluelegged grasshopper is parasitism by the tangleveined fly, Trichopsidea clausa. In some years 80 percent of females in a population are infested with parasitic larvae. A parasitized female is unable to reproduce, as all eggs and soft tissues are consumed by an invading larva. Upon developing to maturity a larva leaves its host, which then dies. Interestingly, the bigheaded grasshopper is not affected by this parasite. The tiny larva, 0.5 mm in length, may invade an individual but it is sealed off and killed by the resistant host.
In the afternoon, activity ceases when temperatures of the soil surface rise to 120°F. The nymphs may rest horizontally on the ground in shade of vegetation or may climb on grasses to a height of 2 inches. Adults may rest horizontally on the ground in the shade of vegetation or they may move into the crowns of grasses and rest diagonally on leaf stems in the shade. Later, when temperatures decline the grasshoppers become active again and begin normal activities. In the evening they bask in the waning rays of the sun and eventually select their night-time locations.
Observations of the species in Montana have revealed that older nymphs and the adults are gregarious. Older nymphs were found in small aggregations while the adults were found in large aggregations.
Anderson, N. L. 1973. The vegetation of rangeland sites associated with some grasshopper studies in Montana. Montana Agr. Exp. Stn. Bull. 668.
Anderson, N. L. and J. C. Wright. 1952. Grasshopper investigations on Montana range lands. Montana Agr. Exp. Stn. Tech. Bull. 486.
Onsager, J. A. and G. B. Mulkern. 1963. Identification of eggs and egg-pods of North Dakota grasshoppers. North Dakota Agr. Exp. Stn. Bull. 446 (Tech.).
Otte, D. 1984. The North American Grasshoppers, Vol. II Acrididae, Oedipodinae. Harvard University Press: Cambridge, Massachusetts.
Pooler, P. D. 1989. Factors influencing grasshopper oviposition site selection on South Dakota rangelands. M.S. thesis, South Dakota State University, Brookings, SD.
York, G. T. and H. W. Prescott. 1952. Nemestrinid parasites of grasshoppers. J. Econ. Entomol. 45: 5-10.
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