Distribution. This native grasshopper is widely distributed in northern North America. In the United States it extends from the Atlantic to the Pacific Oceans, and is absent only from the Gulf Coast region. In Canada it occurs from Nova Scotia to British Columbia.
Host Plants. This species is adaptable, and is found in a variety of habitats. However, it is most abundant in moist meadows, dense vegetation along water courses, and in disturbed, weedy areas. In the Great Plains region it is abundant in moist tallgrass regions, but uncommon in the drier shortgrass prairie. Twostriped grasshopper feeds on both grasses and broadleaf plants, but prefers the latter and fares poorly in habitats lacking broadleaf plants. Plants in the families Compositae and Cruciferae seem to be preferred. Among the uncultivated vegetation consumed is arrowleaved colt's foot, Petasites sagittatus; burdock, Arctium lappa; dandelion, Taraxacum officinale; dog mustard, Eruscastrum gallicum; flixweed, Descurainia sophia; needleleaf sedge, Carex eleocharis; leadplant, Amorpha canescens; oxeye daisy, Chrysanthemum leu-canthemum; pepperweed, Lepidium densiflorum; plantain, Plantago major; redtop, Agrostis alba; sand dropseed, Sporobolus cryptandrus; Canada thistle, Cir-sium arvense; sunflower, Helianthus spp.; wavyleaf thistle, Cirsium undulatum; mustard, Brassica spp; and others. Mulkern et al. (1962) determined the plants consumed by twostriped grasshoppers in North Dakota alfalfa fields, and reported that the plants most often consumed, after alfalfa, were kochia, Kochia sco-paria; wild oat, Avena fatua; awnless bromegrass, Bro-mus inermis; flixweed, Descurainia sophia; marsh elder, Iva xanthifolia; and quackgrass, Agropyron repens. On prairie, however, the plants most often consumed were Kentucky bluegrass, Poa pratensis; leadplant, Amorpha canescens; and western ragweed, Ambrosia psi-lostachya (Mulkern et al., 1964). Survival rates and body weights of twostriped grasshopper are higher, and development times shorter, on mixed diets than on single hosts (MacFarlane and Thorsteinson, 1980). Bailey and Mukerji (1976) were able to culture twostriped grasshopper on nearly all plants tested, though they completed development more rapidly when provided with plants on which they preferred to feed.
Twostriped grasshopper commonly infests vegetable and field crops, though most injury is limited to field margins. Among vegetable crops injured are beet, cabbage, chicory, corn, lettuce, onion, potato and likely others. Field crops such as alfalfa, birdsfoot trefoil, clover, young barley and oat, timothy, vetch and the immature seedheads of wheat also are fed upon. Flowers and ornamental plants likewise are attacked. (See color figure 29.)
Natural Enemies. The natural enemies of the crop-feeding Melanoplus spp. are quite similar. For information on natural enemies of twostriped grasshopper, see the section on natural enemies of migratory grasshopper, Melanoplus sanguinipes (Fabricius).
Weather. Survival and population increase in grasshoppers are favored by hot weather. High numbers tend to occur after a period of years with abnormally hot and dry weather during the spring and summer months. This is especially true in northern areas, where it tends to be cooler. Enough precipitation is required to provide adequate food for grasshoppers, of course, but protracted periods of rainfall during egg hatch, especially if accompanied by cool weather, disrupt feeding by young grasshoppers and induce high mortality. Late onset of winter can favor grasshopper population increase because it allows adults additional time to produce eggs.
Life Cycle and Description. Over most of its range, twostriped grasshopper displays one generation annually, with the egg stage overwintering. In Colorado, eggs begin to hatch in June, though hatching can occur over a four-to-six week period. Nymphs may be present until September, but adults appear beginning in July. Oviposition commences in August and continues until adults are killed by cold weather. At higher elevations in British Columbia, a two-year life cycle is reported (Beirne, 1972).
oviposition period, after which they oviposit within the roots of grasses and weeds. Duration of the ovi-position period is about 30 days (range 15-55 days). (See color figure 166.)
Aspects of the biology of twostriped grasshopper were treated by many authors, including Parker (1939), Shotwell (1941), Church and Salt (1952), and Smith (1966). An excellent synopsis was presented by Pfadt (1994e), who also pictured all stages of development. A summary of twostriped grasshopper biology, including keys to related Canadian Orthoptera, was given by Vickery and Kevan (1985). Melanoplus bivittatus was included in many grasshopper keys, including those by Blatchley (1920), Dakin and Hays (1970), Helfer (1972), Capinera and Sechrist (1982), and Richman et al. (1993). This species was also included in a key to grasshopper eggs by Onsager and Mulkern (1963). Rearing of Melanoplus spp. was described by Henry (1985).
Twostriped grasshopper consumes the leaves of numerous plants. Damage is greatest in areas adjacent to weeds, and along fence rows, irrigation ditches, roadsides, and fallow fields. Damage is exacerbated by drought, which apparently increases nymphal survival rates and decreases the amount of weed vegetation available to the grasshoppers. Although the grasshoppers feed at night if it is sufficiently warm, where nights are cool these grasshoppers tend to perch on elevated objects. This behavior allows them to be warmed by the light from the setting and rising sun, and maximizes their period of activity. This also results in nibbling on the resting substrate by the grasshoppers; these grasshoppers feed on the bark of bushes and young trees, and even damage shingles on buildings and eat holes in vinyl window screens while perching. The nymphs and adults are fairly dispersive, and walk tens or even hundreds of meters in the search for food. At high densities they show propensity to swarm, which is expressed by band formation in the nymphal stage and flight by adults. The temperature threshold for flight is 30-32°C. Ascending to heights of 200-500 m, and flying with the wind, swarming adults can disperse long distances.
Management of the various Melanoplus spp. grasshoppers is substantially the same. For information on twostriped grasshopper management, see the section on management under migratory grasshopper.
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