How Much Do Grasshoppers Weigh

Fourspotted Grasshopper

Phlibostroma quadrimaculatum (Thomas)

P. quadrimaculatum identification
Next Species in Subfamily: Psoloessa delicatula
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Distribution and Habitat

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Wyoming distribution map

The fourspotted grasshopper has a wide distribution in western grasslands. Information technology inhabits the shortgrass, mixedgrass, desert, and bunchgrass prairies. Information technology prefers to feed on blue grama and is commonly establish where this and other shortgrasses are the dominant vegetation. In the mixedgrass prairie where mid grasses and curt grasses grow in mosaic patches, the fourspotted grasshopper occupies the patches of brusque grass. Information technology has been recorded infrequently from the tallgrass prairie just with no description of the specific habitat in which it occurs.

Economic Importance

The fourspotted grasshopper lives in assemblages of grasshoppers inhabiting mixedgrass, shortgrass, and desert prairies of the West. Information technology is usually a subdominant member of the assemblages, but it occasionally becomes the ascendant species. Because it feeds principally on blue grama, a preferred forage establish of livestock, information technology can go a serious pest during grasshopper outbreaks. Estimates based on body weight indicate that an individual of this species ingests ane.4 gm of grass dry weight during its lifetime, an amount less than that eaten by the bigheaded grasshopper, Aulocara elliotti (2.0 gm). The fourspotted grasshopper is a thrifty feeder, cutting down little if any grass. Information technology does much less clipping of forage than the bigheaded grasshopper. Because information technology does non increase to the high densities reached by the latter species, it is not as serious a pest.

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).

Food Habits

The fourspotted grasshopper feeds well-nigh exclusively on grasses. Blueish grama and buffalograss are its preferred nutrient plants, but other species of grasses and sedges are ingested, usually in modest amounts. Examinations of nymphal and adult crop contents show that blue grama makes upwardly 89 to 100 percent of the diet. Six other species of grasses (buffalograss, needleandthread, western wheatgrass, sand dropseed, sideoats grama, and prairie sandreed) have been constitute in ingather contents. In a desert prairie of Texas, ingather contents consisted of 48 pct buffalograss, 21 percent bluish grama, 19 pct burrograss, 5 percent fall witchgrass, v percent Muhlenbergia sp., and 2 percent of an undetermined grass. When given a choice of blue grama and western wheatgrass, caged adults ate but the blue grama.

Individual grasshoppers in the field, nevertheless, may contain a substantial amount of other grasses. For example, ane female inhabiting the shortgrass prairie of Colorado had 40 percentage western wheatgrass in its ingather contents while some other had 43 percent buffalograss. In addition to grasses, a few grasshopper crops have been plant to comprise small amounts of ii sedges (needleleaf sedge and threadleaf sedge) and five species of forbs (prairie onion, fringed sagebrush, hairy goldaster, spreading fleabane, and reddish globemallow).

The fourspotted grasshopper selects green leaves for its food. This species has non been observed to feed on dry out plant litter in its natural habitat. Tests of caged grasshoppers indicated that just six percent of the insects had fed on bran allurement.

Several observations of the feeding of this grasshopper in the mixedgrass prairie of eastern Wyoming signal that it attacks grass in two master ways. A grasshopper may climb up a green leaf of blue grama, turn effectually and feed almost 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 establish to begin feeding on the end of a foliage and progress toward the base.

Dispersal and Migration

The fourspotted grasshopper possesses functional wings, which range in length from being just short of the end of the abdomen to extending beyond the belly by every bit much every bit 5 mm. Specimens with longer wings occur ordinarily in the southern range of the species, as in Texas. Evasive flying is straight, silent, and extends for distances of 2.5 to 5 feet at heights of well-nigh 6 inches. The flying grasshopper usually lands on bare ground and faces abroad from the intruder.

Little is known about its dispersal and migration. Where the bigheaded grasshopper, A. elliotti, has often appeared as accidentals in the mountains west of Bedrock, Colorado, no fourspotted grasshopper has ever been found at that place. Notwithstanding, evidence that the species occasionally disperses comes from a mixedgrass prairie of eastern Wyoming in which this grasshopper occurred at a density of seven nymphs per foursquare yard. An expanse of 840 acres was sprayed in 1970 with an insecticide resulting in the virtual elimination of this species. Non until 1973 was the species institute once more when ane female was encountered in 100 square-foot samples. The following year two nymphs were constitute in 100 square-foot samples. The population manifestly gained a new foothold in the surface area from dispersing adults and began once more to increase.

Identification

Adults of the fourspotted grasshopper are medium sized and strikingly colored (Fig. half-dozen and 7). Lateral foveolae are invisible from above. Side of head has a vertical ivory stripe below chemical compound centre. Four diagnostic marks are on the median expanse of tegmen (Fig. 9). The hind femur has medial area crossed by 3 nighttime oblique bands. Hind tibiae are orangish. The pronotal disk has the median carina cutting in one case near the middle; the lateral carinae are distinct and constricted in the central region.

The nymphs are identifiable past their shape, external structures, color, and color patterns (Fig. 1-5).

1. Head is relatively large, confront moderately slanting; antennae filiform. Instar I with dark brown vertical stripe below compound eye and with dark brown horizontal band backside compound centre that extends onto lateral lobe of pronotum, background color of head ivory. Postgena of head and anteroventral region of lateral lobe colored nighttime brown forming a vertical band that runs nearly parallel with the dark vertical band below chemical 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 ring below chemical compound eye is evident.

ii. Pronotum with lateral carinae ivory-colored and constricted in primal region (Fig. 8), constriction increases equally nymphs molt from 1 instar to the next. Pronotal lobe with diagonal ivory ridge on anterior primal region.

3. Hind femur with medial area about entirely fuscous in instars I to Iii, partly green in instar Iv and 5. Hind tibia tan and gray or pink in late instars.

iv. General colour pattern of instar I ivory with fuscous band extending from backside chemical compound eye to end of abdomen; instars II to V green or occasionally tan, the fuscous band unabridged on side of caput and abdomen, cleaved on lobe of pronotum.

Hatching

The fourspotted grasshopper begins to hatch xv to 25 days later the bigheaded grasshopper, A. elliotti, placing it in the intermediate hatching grouping. Hatching continues for 2 to three weeks. In the mixedgrass prairie of eastern Wyoming and shortgrass prairie of eastern Colorado hatching usually occurs during the first ii weeks of June. Depending on the weather, actual dates of hatching in a site may differ by as much as 15 days between years.

Nymphal Development

Nymphs on the mixedgrass prairie of eastern Wyoming develop slowly, taking an average of 48 days to go adults. At some sites and in certain years the nymphal period may be as brusk as 33 days or as long equally 55 days. There are v nymphal instars in females and unremarkably iv, only occasionally five, in males.

Adults and Reproduction

Adults of the fourspotted grasshopper remain in the same habitat in which the nymphs hatched and developed. The preferred host institute, blue grama, remains dark-green and palatable through the summer and autumn, even during most dry years. In the mixedgrass prairie of eastern Wyoming and shortgrass prairie of eastern Colorado, the adults appear during the latter function of July. Two weeks later, males begin to try copulation with the females. The males are attracted to moving females and may chase afterward them. Females that stop are courted by males, which tip their hind femora and stridulate. Afterward closing in, the males mount and try to appoint their genitalia with those of the females. Females may reject mounted males by producing vibratory stridulation or by shaking the hind femora in a vertical position. The initiation of successful copulation has non been observed, merely copulating pairs have been seen in the morning between ix:45 and 11:45 MDT in late August and early September.

In western Due south Dakota, females take been observed to oviposit into soil adjacent 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 v.two mm long. The eggs laissez passer the winter in the soil, but no study has been made of their embryology. The species has one generation annually.

Population Ecology

The fourspotted grasshopper is a common grasshopper, enjoying a relatively high frequency of occurrence in the mixedgrass and shortgrass prairies. Of 419 sites surveyed in 1991 in the mixedgrass prairie of eastern Wyoming, this species was encountered in 94 locations (22 percent). It occurred mainly every bit a subdominant in rangeland assemblages of grasshoppers, only in five of the 94 sites information technology was the dominant species. A study of the grasshopper fauna in the mixedgrass prairie of Montana in 1953 and 1954 disclosed the presence of the fourspotted grasshopper in 16 of 38 sites (42 percent) and dominance in two locations.

Densities of fourspotted grasshoppers, when subdominant in grasshopper assemblages, ordinarily range from 0.2 to 1.5 young adults per square yard. When the species is ascendant, densities may be as neat as five per square yard. No information is bachelor on how rapidly and under what atmospheric condition populations of this grasshopper ascension to loftier densities and authorization.

In a population inhabiting the mixedgrass prairie of eastern Wyoming, the fourspotted grasshopper persisted for at to the lowest degree eight years at fluctuating, low densities. Densities of this species and the entire assemblage are shown for 5 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 take been found to exist parasitized past flesh fly larvae. Of these larvae, 64 percentage were killed by the host and melanized, thereby reducing the negative impact of the parasite on population growth of the host.

Daily Activity

The fourspotted grasshopper is a basis-dwelling insect. At night both nymphs and adults sit horizontally on small-scale areas (1 to 8 square inches) of bare ground or litter that are surrounded by blue grama and threadleaf or needleleaf sedge. They may likewise rest under a canopy of mid grasses. One to two hours after sunrise, they begin to bask horizontally on the footing by exposing a side perpendicular to the sun's rays. They normally raise exposure of the belly by lowering the associated hindleg, which is held flexed and parallel with the abdomen. Basking lasts for one or two hours. When temperatures of the soil and air have risen above lxx°F, the grasshoppers gradually become active and brainstorm to potter, feed, and mate. They continue these activities until temperatures get too hot. When soil surface temperature reaches 100°F, grasshoppers horizontally positioned on bare footing presume a stilt posture in which they heighten their bodies every bit high as their legs volition extend. When temperatures rise still further (120°F soil surface), they have positions 1/ii to 4 inches higher up basis level on blue grama plants and face the lord's day. In this orientation they have moved away from the hot bare ground and expose a minimum of body surface to the sun'due south rays; they may also spread apart the hindlegs to increment cooling. Two hours before sunset the grasshoppers again bask. Later basking and earlier sunset they move to their nighttime positions.

Selected References

Alexander, G. and J. R. Hilliard, Jr. 1969. Altitudinal and seasonal distribution of Orthoptera in the Rocky Mountains of Northern Colorado. Ecol. Monogr. 39: 385-431.

Anderson, N. L. 1973. The vegetation of rangeland sites associated with some grasshopper studies in Montana. Montana Agr. Exp. Stn. Balderdash. 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 Direction 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., One thousand. 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 written report of communicative behavior in grasshoppers. Univ. Michigan Mus. Zool. Misc. Publ. 141.

Pfadt, R. Due east. 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.Southward. thesis, South Dakota State Academy, Brookings, SD.

Przybyszewski, J. and J. L. Capinera. 1991. Patterns of parasitism amid shortgrass prairie grasshopper (Orthoptera: Acrididae) populations. J. Kansas Entomol. Soc. 64: five-17.

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