Wyoming distribution map
The cudweed grasshopper inhabits grasslands east of the Rocky Mountains. It has an irregular distribution due to variations in distribution of its host plant, cudweed sagewort, Artemisia ludoviciana. The insect is not entirely coexistent with its host plant, which occurs farther in all directions and at altitudes considerably higher than the grasshopper. In Colorado the cudweed grasshopper has not been found higher than 6,000 feet.
Of ecological interest is the observation that the cudweed grasshopper is the only species of grasshopper able to survive on cudweed sagewort. The leaves of this plant are pubescent, but the hairs do not interfere with the consumption and digestion of leaf tissue by the cudweed grasshopper. Although the hairs do not deter attack by polyphagous species, they apparently interfere with digestion of leaf tissue as indicated by the response of the migratory and twostriped grasshoppers. These two species are unable to grow normally on this plant because, it is suggested, digestion is abnormally energy-expensive.
Laboratory studies of Kansas populations revealed details of feeding by this grasshopper on its host plant. The younger nymphs (instar I to III) fed from the upper, less hairy surface of leaves by gouging out leaf tissue. This injury left thin areas and holes within the leaf margins. Older instars and adults fed on the edges of leaves. Samples of injured plants from rangeland 6 miles northwest of Fort Collins, Colorado indicated that cudweed grasshoppers preferred the young top leaves.
The nymphs are identifiable by their shape, structures, and color (Fig. 1-5).
1. Head pale green and spotted brown, antennae of instar I blue and each segment with anterior pale annulus, antennae of instars II to V green and segments with anterior pale annuli, segments of instars III to V with brown spots or suffusions of brown.
2. Pronotum pale green and spotted brown, median carina paler green, this dorsal line runs from median carina onto meso and metanotum and the abdomen; medial area of hind femur pale green and spotted brown or medium green; hind tibia pale green.
3. Abdomen pale green and spotted brown.
Collections of grasshoppers from rangeland may include nymphs of Hypochlora alba and Hesperotettix viridis. Both species are spurthroated grasshoppers and green. The two can be separated by the following characteristics. 1. H. viridis is medium green, H. alba pale green. 2. Antennae of H. viridis are black with segments having a pale anterior annulus, H. alba have green antennae and may be spotted or suffused with brown in the older instars. 3. H. viridis has medial area of hind femur medium green and spotted black in instars I and II, and medium green with black chevrons in instars III to V, H. alba has the medial area of hind femur pale green and spotted brown or medium green.
As measured from first hatch to first adults, the nymphal period lasts 44 to 46 days (Table 1). Both males and females require five instars to achieve adulthood.
No investigation of maturation and courtship have been conducted. Observations of two pairs in copulo were made 12 August 1994 at 6:46 a.m. and at 9:25 a.m. DST in a mixedgrass prairie site of northcentral Colorado (altitude 5,400 feet). One pair rested 1.5 inches from the tip of a 10-inch tall cudweed plant; the other pair inhabited a cudweed patch, but its position was not noted. Adults were observed in this Colorado site from July 31 to October 4, 1993. The population dwindled in density as the season progressed. Females oviposit in the interspersed bare areas of grassland. During oviposition, the female holds on to an upright plant, and with hindlegs held high, works her ovipositor into the soil. A record of one complete oviposition revealed that drilling began at 3:10 p.m. and egg laying finished at 4:25 p.m. The female then devoted several minutes to movement of soil particles over the cavity with her ovipositor. The pod is slightly curved, 5/8 to 3/4 inch long, and contains 8 to 12 eggs (Fig. 9). The eggs are tan and 3.8 to 4.9 mm long. In the ground, the eggs are oriented nearly vertically.
The steady persistence of the cudweed grasshopper in sites with an abundance of their host plants was shown in a study of grasshopper assemblages inhabiting the sand prairie of southeastern North Dakota. The study revealed the presence of populations of the cudweed grasshopper every year from 1959 to 1969. The relative abundance of the species fluctuated from 7.3 percent of the grasshopper assemblage in 1959 to 2.2 percent in 1964. The study also showed that the cudweed grasshopper was an important member of the forb-feeding group in the sand prairie. Studies in Kansas have shown this species to be numerically important also in the tallgrass prairie. Of 8,100 grasshoppers collected methodically by sweep net from 1982 to 1986 at six sites in native tallgrass prairie (Konza Prairie Kansas), the cudweed grasshopper was fourth in abundance. Ranks of the five dominant species were the following: Phoetaliotes nebrascensis comprised 54 percent of the total; Melanoplus scudderi, 14 percent; Orphulella speciosa, 11 percent; Hypochlora alba, 7 percent; and Melanoplus keeleri, 6 percent. Of the forb feeders, M. scudderi ranked first, H. alba ranked second, and M. keeleri third.
As soon as the rays of the rising sun strike them, they adjust their positions on the plant to take full advantage of the warming rays. Still in a vertical, head-up orientation, they turn a side perpendicular to the sun's rays and lower the associated hindleg to expose the abdomen more fully. After basking for approximately two hours, they begin to stir, move, and feed. Although mating pairs have been observed as early as 6:45 a.m. DST, the specific time of courting and joining is unknown. Also unknown is the time of day in which oviposition occurs. During the day most individuals observed on the host plant are resting quietly. A few observations have been made of their movements. For example, a female was observed at 10:13 a.m. basking 6 inches above ground on the north side of a cudweed stem; at 10:15 a.m. she backed down 2 inches, then pivoted 45° to the east side of the stem and climbed 2 inches, and then she turned to the west side of the stem; at 10:17 a.m. she fed briefly; by 10:26 a.m. she had moved to the top of the plant (8 inches) in a vertical head-up orientation; at 10:30 she was flushed by the observer in attempting to get a closer look. Adults have also been observed to jump appetitively 2 to 8 inches from one stem to another or to a higher position on the same stem.
When disturbed, both nymphs and adults often jump 2 to 8 inches from one stem of cudweed to another, retaining a vertical head-up orientation. They may jump just once or several times before settling down. Occasionally they may jump as much as 2 feet and land on the ground, but then almost immediately they jump back onto a nearby host plant. Unlike Chorthippus curtipennis, they do not drop to the ground to evade a potential predator. To avoid overheating at high air temperatures (100°F and above) cudweed grasshoppers already several inches above the hot soil surface simply move to the shady side of the plant stem in their usual vertical, head-up orientation. For night shelter they stay and rest on the main stem of the host plant in the same characteristic orientation.
Campbell, J.B., W.H. Arnett, J.D. Lambley, O.K. Jantz, and H. Knutson. 1974. Grasshoppers (Acrididae) of the Flint Hills native tallgrass prairie in Kansas. Kansas Agr. Exp. Stn. Research paper 19.
Criddle, N. 1935. Studies in the biology of North American Acrididae: development and habits. Proc. World's Grain Exhibition and Conference, Regina, 1933. Can. Soc. Agriculturists 2: 474-494.
Evans, E.W. 1988. Community dynamics of prairie grasshoppers subjected to periodic fire: predictable trajectories or random walks in time. Oikos 52: 283-292.
Knutson, H. 1982. Development and survival of the monophagous grasshopper Hypochlora alba (Dodge) and the polyphagous Melanoplus bivittatus (Say) and Melanoplus sanguinipes (F.) on Louisiana sagewort, Artemisia ludoviciana Nutt. Environ. Entomol. 11: 777-782.
Mulkern, G.B. 1980. Population fluctuations and competitive relationships of grasshopper species (Orthoptera: Acrididae). Trans. Am. Entomol. Soc. 106: 1-41.
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