Peranabrus scabricollis Thomas Orthoptera Tettigoniidae

Natural History

Distribution. These similar insects are native to western North America. Mormon cricket occurs widely, with a range that includes southern British Columbia to Manitoba in the north, and south to northern California and northern New Mexico. As a persistent pest, however, its range is limited to the Rocky Mountain and Great Basin regions. Coulee cricket is more limited in occurrence, and is known from Montana, eastern Washington, northeast Oregon, and southern British Columbia.

Host Plants. These crickets are often considered to be omnivorous, but despite their wide host range they display some specific preferences unless confronted by starvation. Among the vegetables damaged by crickets are bean, beet, cabbage, cantaloupe, carrot, cauliflower, Chinese cabbage, corn, lettuce, onion, potato, pumpkin, radish, rutabaga, salsify, spinach, tomato, turnip, and likely others. Not readily eaten are pea and mustard. Other crops susceptible to injury are alfalfa, barley, clover, flax, millet, oat, sugarbeet, sweetclover, timothy, and wheat. Due to the nature of the cropping systems in the areas inhabited by these crickets, alfalfa and wheat are most often injured.

Over 400 species of grasses, forbs, trees and shrubs were reported by Swain (1944) to be eaten by Mormon cricket. Most of these records occurred during the arid "dust-bowl" era of the 1930s when cricket densities were extremely high. Thus, they are not typical of cricket feeding behavior. Crickets often feed preferentially on the flowers and seed-heads of plants, ignoring the leaf material. Seed-head consumption is especially pronounced in grasses, though grasses are a minor component of cricket diet. Forbs such as bitterroot, Lewisia rediviva; wild onion, Allium spp.; arrowleaf bal-samroot, Balsamorhiza sagittata; wild mustard, Brassica spp.; tumblemustard, Sisymbrium altissimum; and lupine, Lupinus spp.; are preferred by nymphs. In the adult stage, crickets eat mostly big sagebrush, Artemisia tridentata (MacVean, 1987; Redak et al., 1992). In an analysis of Mormon cricket diet in Colorado, Ueckert and Hansen (1970) reported that the diet consisted of forbs 50%, arthropods 21%, fungi 16%, grasses 6%, clubmoss 5%, and grasslike plants 2%.

Crickets actively prey on other insects, including cicadas, ants, aphids, and beetles if they have the opportunity to catch them. They are quick to consume injured or dead crickets as well, and one of the distinctive characteristics about these crickets is their tendency to stop and feed on comrades that have been crushed on roadways by vehicles. As the healthy crickets remain on the highways to feed on fallen crickets, they often become crushed also, resulting in long, dark, greasy road slicks consisting of pulverized crickets.

Natural Enemies. Predators are perhaps the best-known mortality factor associated with crickets. Destruction of crickets in 1848 by California gulls, Larus californicus, saved the early Mormon settler's grain crops; a fact commemorated by a large statue of the gulls in Salt Lake City. Gulls are not the only vertebrates attracted to these insects when they become numerous, and among the avian predators most commonly observed feeding on crickets are crows, Corvus brachyrhynchos; hawks, Falco spp. and possibly others; meadowlarks, Sturnella magna; and blackbirds, various species (Wakeland, 1959). Mammals such as coyotes, Canis latrans; ground squirrels, Citellus spp.; and kangaroo rat, Dipodomys spp. also feast on crickets when they are abundant. Also, the wasps Palmodes laeviven-tris (Cresson) and Tachysphex semirufus (Cresson) (both Hymenoptera: Sphecidae) capture crickets and feed them to their young. Despite the frequency at which predation is observed, there is little evidence that predators are normally effective at maintaining crickets at low densities, or capable of suppressing crickets during periods of population outbreak.

Parasitism is surprisingly uncommon in cricket populations. Only the egg stage is parasitized with any degree of frequency, and though levels of up to 50% parasitism have been reported, it is usually quite low. The parasitoids responsible for attacking eggs are Sparaison pilosum Ashmead (Hymenoptera: Scelioni-dae) and Oencyrtus anabrivorus (Hymenoptera: Encyr-tidae). A fly, Sarcophaga harpax Pandelle (Diptera: Sarcophagidae), has been reared from adult crickets, but occurs infrequently.

Pathogens vary greatly in their effect on crickets. The microsporidian Heterovesicula (Vairimorpha) cowani can naturally infect substantial proportions of Mormon cricket populations, and causes rapid mortality when young crickets ingest spores (MacVean and Capinera, 1991,1992; Lange et al., 1995). Heterovesicula appears to be the most important pathogen of crickets. The report that the grasshopper-infesting microspori-dian Nosema locustae can infect Mormon cricket (Henry and Onsager, 1982) seems to be premature. The nema-tode Agamaspirura anabri (Nematoda) (Christie, 1930)

and the horsehair worm Gordius robustus (Nemato-morpha) (Thorne, 1940) have also been observed in crickets. Gordius was reported to be quite common in crickets near standing water, because part of the horsehair worm's life cycle takes place in water; unfortunately, water is not plentiful in the habitat of these crickets.

Life Cycle and Description. The life cycle and description of Mormon cricket and coulee cricket are nearly identical. Normally there is one generation per year, though there are reports of eggs at high altitudes remaining in diapause for an entire year, resulting in a two-year life cycle. They overwinter, with egg hatch occurring in March-May, often while snow remains on the ground. The nymphs are present until June when adults begin to emerge and start egg production. Adults usually perish by late August, often earlier. About 100 days is required for the nymphal and adult stages to be completed. Mormon cricket and coulee cricket are differentiated by the texture of the dorsal surface of the pronotum; it is punctate or rough in coulee cricket but smooth in Mormon cricket.

  1. The egg is elliptical and measures about 78 mm long and 2.0-2.5 mm wide. Initially, brown in color, it soon turns whitish and then gray. They are deposited in the soil singly or in small clusters at a depth of 6-25 mm during the summer, where they remain until spring. One end of the egg, where the head of the embryo is located, swells slightly before egg hatching. Sometimes they are deposited around the base of plants, but more often bare soil is favored, including the mounds of ants. Females deposit, on average, about 85 eggs, but up to 160 per female has been observed. They complete their embryonic development in the summer and autumn, before entering diapause. Thus, they are ready to emerge early in the spring, and begin to hatch when soil temperature attain about 5°C, a much lower temperature than the threshold of development for hatch of grasshoppers. (See color figure 264.)
  2. Upon hatching from the soil, the nymphs are dark, resemble the adults, and measure about 6 mm long. There are seven instars, and by the time they attain the last instar they are about 30 mm long. The initial instars are black with white along the lateral edge of the posterior end of the pronotum, and the ovipositor of the female is not apparent. As they attain the fourth instar, however, they acquire green, red, purple, or brown color and in the female the ovipositor becomes increasingly obvious. Mean duration (range) of development period of crickets cultured at 21-26°C is 9.5 (7-12), 7.4 (4-14), 5.1 (4-7), 6.5 (4-10), 5.6 (3-9),
  3. 6 (5-7), and 10.4 (5-15) days, respectively, for instars 1-7. Thus, the mean total development time of nymphs is estimated at 50 days (range 43-58 days) but weather, and probably density, can significantly affect development rate. Mature nymphs have small wings but the wings do not protrude from beneath the pronotum.

The crickets tend to aggregate, seeking shelter together beneath bushes and debris during inclement weather and at night. Once they reach the third or fourth instar crickets the aggregations begin to move long distances, with numerous crickets coalescing into groups, which move in bands. The density of crickets in bands may be 10-30 per sq m, but sometimes much lower. The width of a band is often 300 m or more, but only 10 m deep, with crickets moving in the same direction along the entire width. The crickets all seem to move independently and consistently in the same direction, often at 1 km per day. There is no indication that they follow one another, and the basis of orientation is unknown. Bands moving in different directions sometimes converge and then emerge without loss of individual band integrity.

Adult. The adult is very similar to the mature nymph in form and color but larger, measuring 3545 mm long. Also, the sword-shaped ovipositor of the adult female is longer, and the short wings of the adult male protrude from beneath the pronotum and are used as a stridulatory organ. As happens with nymphs, the adults may cluster under shelter both during the evening and inclement weather. They can also climb into bushes to escape the hot soil during excessively warm weather. Adults continue to move in bands in the same manner as nymphs, stopping only to eat and oviposit. (See color figure 162.)

Reproduction commences 10-14 days after attaining the adult stage. Males call from perches on vegetation during the morning hours. Females compete for the attention of males, mount the males, and are inseminated. Males are selective in their choice of partners, often choosing the largest female with which to mate. During insemination the male provides the female, attached to the sac containing sperm, a large proteinac-eous mass that protrudes from her genital opening. While the sperm is draining into the female's reproductive system the proteinaceous mass provides a meal for the female. This is a significant investment on the part of the male, as the sperm and its accompanying protein meal represents up to 25% of his body weight (Gwynne, 1984). Breeding usually occurs in hilly areas where vegetation is sparse.

Mormon cricket (and presumably coulee cricket) exist in solitary and gregarious forms. The aforemen-

Adult female Mormon cricket.

tioned description applies mostly to the gregarious form. Only this damaging form has been thoroughly studied. The solitary form occurs at low density between periods of population outbreak and in areas where crickets do not become numerous. In contrast to the gregarious form, solitary crickets are green, and do not aggregate or form bands. Sexual behavior is also reversed, with females choosing among males. This change in mating behavior seems to be related to better nutrition of crickets when they are not at high densities (Gwynne, 1993).

Biology of Mormon cricket was described by Cowan (1929), and of coulee cricket by Melander and Yothers (1917). The impact of Mormon cricket was summarized by Wakeland (1959), and a modern review was given by MacVean (1987). A key to Mormon and coulee crickets, and their near relatives, was published by Rentz and Birchim (1968). Pfadt (1994c) provided a concise summary of Mormon cricket biology and pictures all stages of development. Synopses of Mormon cricket and coulee cricket, including keys to related Canadian Orthoptera, were given by Vickery and Kevan (1985).

Damage

Mormon and coulee crickets occur in arid sagebrush rangeland, and generally cause little injury unless they move into irrigated cropland. In earlier times, when settlers had to be nearly self-sufficient, vegetable gardens were critically important to ranchers, and crop losses caused by Mormon and coulee crickets were a significant threat to the existence of western communities. Now, however, vegetable production is much less significant in these arid lands, and control technologies have improved markedly, so cricket importance has declined. Crickets remain a threat, however, and when bands of crickets invade lush crop vegetation, they can cause serious defoliation.

Management

  1. Cricket bands are easily detected when they cross roads, and their presence in an area rarely is a surprise. However, they move rapidly and their course of travel is unpredictable, so when crickets are discovered control efforts are usually directed at the bands before they enter crop-growing areas. Some areas, usually mesas, seem to support continuous breeding populations, and serve as a source of crickets for nearby regions.
  2. Persistent insecticides are sometimes applied by aircraft to foliage in areas supporting nymphal populations or migrating bands. An alternative is to apply insecticide-treated bait. The preferred bait is flaky wheat bran, and it may be applied dry or with 10% water, but other additives such as molasses do not increase effectiveness (Cowan and Shipman, 1940).

Cultural Practices. In earlier times, a common practice to prevent invasion of crop fields by cricket bands was to surround the crop with ditches possessing steep sides; crickets falling into such ditches had great difficulty regaining the soil surface. Similarly, vertical barriers of metal topped by a deflector served to prevent crickets from entering areas surrounded by such "cricket fences."

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