Grasshoppers | ||
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 by Daniel Otte Academy of Natural Sciences, Philadelphia |
| Grasshoppers (Orthoptera:Acrididae) are perhaps the most important grazing herbivores in the nation's grasslands, which from a human standpoint, are the most important food-producing areas. The damage that grasshoppers do to plants varies with the species. A few dozen species at most are highly injurious to crops, while those that feed on economically unimportant plants may have no measurable impact, and those that feed on detrimental plants are highly beneficial. Given such differences, it becomes important to distinguish properly between harmful and beneficial species. Grasshopper abundance in all kinds of grasslands means they are an important factor in the ecological equation. Their economic importance--positive and negative--means that they must be included in all studies of grassland and desert-grassland communities. | ||
Taxonomic Status |
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| More than 1,000 species of grasshoppers have been described from the United States (Otte 1976, 1994, unpublished data base). Taxonomic revisions at the Academy of Natural Sciences in Philadelphia (ANSP) reveal that approximately 20% of the U.S. species represented in the existing ANSP collection are undescribed (Otte 1981; unpublished data). Most new species belong to the very large genus Melanoplus, which contains some of the most injurious grasshopper species known. A considerable number of undescribed species are from the eastern states, from approximately central Texas to New England. New species are turning up even in extremely well-studied areas such as Michigan and Florida. It is expected that at least tens of species remain to be discovered in the coastal ranges of California, and many other mountain peaks in the western states should have species unique to them. Much of the academy's collecting efforts have been directed to investigating the grasshopper faunas of such mountain peaks ("sky islands"). | ||
Natural Range Increases |
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| Great Lakes Region | ||
| Documenting natural range changes requires that comparable collections be made at several points in time. The only such case involving grasshoppers that I am aware of involves the ranges of two grasshopper species along the Great Lakes shores. Trimerotropis huroniana and T. maritima displace one another on the dunes surrounding the Great Lakes, with T. huroniana occupying the northern shores and T. maritima the southern shores (Otte 1970). The boundary between these two species has shifted in the last seven decades. The two species may well be competitive on four different lakefronts, on the north-south shores of Lakes Michigan and Huron. | ||
| Prairie Peninsula | ||
| In southern Michigan the bandwing grasshopper (Pardalophora haldemani) was abundant in 1943 and the related species, P. apiculata, was rare (Cantrall 1943). By 1968 P. haldemani had been completely replaced by P. apiculata, probably because subtle habitat changes gave P. apiculata an advantage over the strictly prairie species P. haldemani. | ||
Unnatural Range Increases |
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| Precise documentation of range changes in grasshoppers could be achieved if historical collecting sites could be resurveyed today. We are reasonably certain, though, that the cutting of eastern forests (mainly during the last century) opened up habitats for numerous species adapted to grasslands and forest edges. Numerous prairie margin species now occur widely in the eastern United States in areas that were almost completely covered by forests. By colonizing roadsides, other species have become extremely widely distributed. The Carolina locust (Dissosteira carolina), for example, is a ubiquitous roadside species that is now found in previously heavily forested regions. Whether the overall range (outer limits of the range) has changed is debatable because the species inhabits river margins and small natural eroded areas within the eastern forest region. | ||
| In the western United States, certain species do well in eroded habitats that often result from overgrazing. Thus, the ranges of species specializing on eroded ground probably increased along with increases in grazing. The clearwinged grasshopper (Camnula pellucida), a pest species from the northern Great Plains that greatly damages crops in the northern United States and western Canada, is now extremely abundant in overgrazed mountain meadows in the western states and is a good indicator of meadow degradation there. | ||
| Many pest species specialize on agricultural fields; their ranges have increased because of irrigation and the planting of crops in normally desert habitats (e.g., migratory grasshopper [Melanoplus sanguinipes], two-striped grasshopper [M. bivittatus], and differential grasshopper [M. differentialis]). Ball et al. (1942) documented numerous cases of grasshoppers moving into areas altered by agricultural practices. | ||
Range Reductions and Extinctions: Case Studies |
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| The Rocky Mountain Locust | ||
| Although it was the most abundant species during much of the last century in western North America, the Rocky Mountain locust (M. spretus) is now extinct; no specimens have been collected in this century. This species spread its destruction over many western states and was the source of great difficulty for early farmers east of the Rocky Mountains. The complete disappearance of the species has puzzled biologists for decades. The most reasonable hypothesis is that this species reproduced mainly along river valleys in Montana and Idaho and that with the heavy grazing of these habitats, beginning in the last part of the 1800's, these breeding areas were so heavily disturbed that breeding was disrupted (Lockwood and DeBrey 1990). Today, frozen remains of this species can still be found in glaciers in Montana. | ||
| California Coastal Ranges | ||
| The ANSP collections revealed that two undescribed species of Melanoplus were collected only in what is now downtown San Francisco. Recent revisions of the Marginatus group of the genus Melanoplus (Otte 1981, 1994, unpublished data base) reveal that the coastal ranges of California contain numerous members of this group, but that the ranges of many of the species are extremely limited. A subgroup of the Marginatus group speciated around the San Francisco Bay area, two species are known from the Berkeley area, two from San Francisco proper, and several from the north side of San Francisco Bay. The San Francisco species were collected in the first decade of this century when some natural vegetation still existed in San Francisco. South of San Francisco these species are replaced by related species. Several other species in the group are known only from the Monterey Bay region, and one species only from a single locality. | ||
| Two Rare Species | ||
| Two individuals of an extremely rare grasshopper species (Eximacris superbum Hebard) were collected in south Texas. Repeated efforts to collect the species have not met with success, although the species possibly breeds only during winter or in the early spring and might still turn up when an effort is made to collect it in early spring. The only relative in this genus (E. phenax Otte) is known from a single male collected at Big Cedar in the Kiamichi Mountains of Oklahoma. Searches for this species have also been unsuccessful; again, it is possible that the species overwinters in the adult stage and therefore is not present during normal grasshopper breeding times. | ||
| Mountain Islands | ||
| Some species of grasshopper are known only from mountain tops (sky islands). In the East, some Melanoplus species are known from single balds (grassy mountain summits) in the Appalachian region (three new species are presently being described; Otte, unpublished data). In the western United States members of the Montanus group are also known only from single localities (A.B. Gurney, unpublished data). Surveys of mountains in Colorado, New Mexico, Arizona, Utah, and Nevada showed that some of these species have not yet been described and are believed to occur only on single mountains. | ||
| Within their limited ranges on mountains, the grasshopper species are further limited by environmental disturbance. I have encountered many overgrazed mountain meadows, sometimes even highly isolated ones surrounded by forest. These differ from ungrazed meadows chiefly in the height of the vegetation and the number of plant species there, and consequently in the incidence of short-winged grasshoppers. Collections from high mountain passes, where meadows are partly protected from cattle by fences along the road, show a clear effect of vegetation length on diversity: in the protected areas, nonflying grasshopper species are present, sometimes in large numbers, but are absent in grazed areas, while flying species, which have wide distributions (weedy species), are common. The principal reason for the difference appears to be that short-winged, nonflying species are highly vulnerable to bird predation, and without protective vegetation are unable to survive. | ||
| Pleistocene Islands in Northern Florida | ||
| The northern half of Florida contains a number of habitats that remained exposed as islands during interglacial periods. Several grasshopper groups have species associated with these former islands and species' ranges are highly restricted (Hubbell 1932). These areas are also ideal for farming and therefore have been greatly altered during the last 50-80 years. It is extremely likely that some species never collected were lost. It remains to be seen which species collected earlier this century still exist. | ||
Management Implications |
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| Large differences exist in range sizes between species that can fly and those that cannot (Otte 1979). In the latter group are numerous species known from a single or a few localities. Most of these inhabit island habitats (isolated bogs, prairie openings within the eastern forests, balds on the Appalachian range, mountain meadows on western mountaintops, hammocks in Florida, and perhaps coastal islands along the East coast). Many species in these regions have probably already been lost. Others can be saved by creating new sanctuaries and properly modifying existing ones. Within such regions it should be possible to set aside small sanctuaries or strings of sanctuaries from which cattle and other grazing mammals are excluded. Such sanctuaries already exist along highways where cattle are kept away from roadsides and railways. | ||
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Academy of Natural Sciences Department of Entomology 1900 Benjamin Franklin Parkway Philadelphia, PA 19103 |
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| References | |
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Ball, E.D., E.R. Tinkham, R. Flock, and C.T. Vorhies. 1942. The grasshoppers and other Orthoptera of Arizona. Tech. Bull. Arizona College of Agriculture 93:275-373. Cantrall, I.J. 1943. The ecology of the Orthoptera and Dermaptera of the George Reserve, Michigan. Miscellaneous Publ. of the University of Michigan Museum of Zoology 54:1-184. Hubbell, T.H. 1932. A revision of the puer group of the North American genus Melanoplus, with remarks on the taxonomic value of the concealed male genitalia in the Cyrtacanthacridinae (Acrididae). University of Michigan Museum of Zoology Miscellaneous Publ. 23:1-64. Lockwood, J.A., and L.D. DeBrey. 1990. A solution for the sudden and unexplained extinction of the Rocky Mountain locust, Melanoplus spretus (Walsh). Environmental Entomology 19:1194-1205. |
Otte, D. 1970. A comparative study of communicative behavior in grasshoppers. University of Michigan Museum of Zoology Miscellaneous Publ. 141:1-168. Otte, D. 1976. Species richness patterns of New World desert grasshoppers in relation to plant diversity. Journal of Biogeography 3:197-207. Otte, D. 1979. Biogeographic patterns in flight capacity of Nearctic grasshoppers (Orthoptera, Acrididae). Entomological News 90(4):153-158. Otte, D. 1981. The North American grasshoppers. Vol 1. Acrididae: Gomphocerinae and Acridinae. Harvard University Press, Cambridge, MA. 275 pp. Otte, D. 1994. The Orthoptera species file: computer catalog to the genera and species of world grasshoppers. Academy of Natural Sciences of Philadelphia. Unpublished data base. |