Distribution. These mole crickets were inadvertently introduced to the southeastern United States in about 1900. Shortwinged mole cricket, Scapteriscus abbreviatus Scudder, was first observed at Tampa, Florida in 1899, but separate introductions were discovered near Miami in 1902 and Brunswick, Georgia in 1904. Southern mole cricket, Scapteriscus borellii Giglio-Tos (known until recently as S. acletus Rehn and Hebard), was similarly introduced to major seaports, beginning with Brunswick in 1904, and followed by Charleston, South Carolina in 1915, then Mobile, Alabama in 1919, and finally Port Arthur, Texas in 1925. Tawny mole cricket, Scapteriscus vicinus Scudder, was first observed at Brunswick, Georgia in 1899. The origin of these crickets is uncertain, but Argentina and Uruguay are likely sources, because they occur in these areas of southern South America.
In the years since introduction to the United States, the Scapteriscus spp. have expanded their ranges, but they differ considerably in their current distribution. Shortwinged mole cricket, which is flightless, remains fairly confined to the southern Florida and southern Georgia-northeast Florida introduction sites, though it also occurs in Puerto Rico and the Virgin Islands. It has been redistributed in southern Florida, but is largely found in coastal areas. In contrast, southern mole cricket is now found from North Carolina to eastern Texas, including the northern regions of Georgia and Alabama and the entire peninsula of Florida, and recently was detected in Yuma, Arizona. Tawny mole cricket is somewhat intermediate in its spread; it occurs from North Carolina to Louisiana, and throughout Florida, but thus far remains restricted to the southern coastal plain.
These are not the only mole crickets found in North America, but they are most damaging. For example, a native species, the northern mole cricket, Neocurtilla hexadactyla (Perty), is widely distributed in the eastern states west to about South Dakota and Texas, and including southern Ontario, but is not a pest. European mole cricket, Gyllotalpa gryllotalpa (Linnaeus), has been introduced from Europe into the northeastern states, but is of minor significance. Changa, Scap-teriscus didactylus (Latreille), invaded Puerto Rico from South America before 1800, and has caused considerable damage to crops on this island.
Host Plants. Mole crickets are omnivorous, feeding on animal as well as plant material. Several studies have indicated that when provided with grass or collected from grass-dominated habitats, southern mole cricket is less damaging than tawny mole cricket. Southern mole cricket feeds mostly on other insects, whereas tawny mole cricket is principally herbivorous (Matheny, 1981; Matheny et al., 1981; Walker and Ngo, 1982). Both species are associated with tomato and strawberry fields (Schuster and Price, 1992). Among vegetable crops reported to be injured are beet, cabbage, cantaloupe, carrot, cauliflower, collards, eggplant, kale, lettuce, onion, pepper, potato, spinach, sweet potato, tomato, and turnip. Other plants injured include chufa, turf, and pasture grasses, peanut, strawberries, sugar cane, tobacco, and such flowers as coleus, chrysanthemum, and gypsophila. Among the turf grasses, bahiagrass and Bermudagrass are commonly injured by tawny mole cricket, whereas St. Augustine grass and Bermudagrass are favored by shortwinged mole cricket. Mole crickets also feed on weeds such as pigweed, Amaranthus spp.
Natural Enemies. Few natural enemies of Scapter-iscus mole crickets exist naturally in North America. Among the natural enemies are amphibians such as toads, Bufo spp.; birds such as sandhill cranes, Grus canadensis; and mammals such as armadillos, Dasypus novemcinctus. They, and the few predatory insects that attack crickets such as tiger beetles (Coleoptera: Cicin-delidae), are not effective. Therefore, several natural enemies have been introduced from South America (Parkman et al., 1996). The most effective introduced beneficial insect is the parasitoid Ormia depleta (Wiede-mann) (Diptera: Tachinidae), which was imported from Brazil. This fly is attracted to the calls of male mole crickets. Its release has resulted in reduced mole cricket injury in southern Florida (Frank et al., 1996). A less effective parasitoid is Larra bicolor Fabricius (Hymenoptera: Sphecidae), which was imported from Bolivia but seems to be constrained by availability of suitable adult food sources in Florida (Frank et al., 1995). An entomopathogenic nematode, Steinernema scapterisci, was introduced from Uruguay (Nguyen and Smart, 1992). It is fairly specific to mole crickets, persists readily under Florida's environmental conditions, and is dispersed by crickets. Field collections consistently show infection levels of 10% or greater (Parkman et al., 1993a,b; Parkman and Smart, 1996), and infected crickets die within 10-12 days.
Life Cycle and Description. Southern and tawny mole cricket are quite similar in appearance and biology. Shortwinged mole cricket differs in appearance owing to the short wings but also in behavior, because it has no calling song and the short wings render it incapable of flight. Typically, the eggs of these three species are deposited in April-June, and nymphs predominate through August. Beginning in August or September some adults are found, but overwintering occurs in both the nymphal and adult stages. Maturity is attained by the overwintering nymphs in April, and eggs are produced at about this time. A single generation per year is normal, though in southern Florida there are two generations in southern mole crickets and an extra peak of adult flight activity in the summer, resulting in spring, summer, and autumn flights from the two generations (Walker et al., 1983).
Shortwinged mole cricket bears front wings that are shorter than the pronotum. The front wings cover the hind wings, which are minute. The body is mostly whitish or tan in color, though the pronotum is brown mottled with darker spots. Also, the abdomen is marked with a row of large spots dorsally, and smaller spots dorsolaterally. These crickets measure 22-29 mm long. The two dactyls on the foretibiae are slightly divergent, and separated at the base by a space equal to at least half the basal width of a dactyl. Shortwinged mole cricket makes no calling song, producing only a weak 1-5 pulse chirp during courtship. (See color figures 159 and 171.)
Southern mole cricket has long hind wings that extend beyond the tip of the abdomen. The front wings are longer than the pronotum, about two-thirds the length of the abdomen. They are broad and rounded at the tips. This cricket is brown, with the dorsal surface of the pronotum often quite dark. As with short-winged mole cricket, in southern mole cricket the two dactyls on the foretibiae are separated at the base by a space equal to at least half the basal width of a dactyl. Thus, these two species can be distinguished by the wing length. Southern mole cricket produces a calling song that consists of a low-pitched ringing trill at about 50 pulses per second. It usually is emitted during the first two hours after sunset. (See color figure 161.)
Tawny mole cricket is quite similar to southern mole cricket in general appearance, with moderately long front wings and long hind wings, a yellowish brown body, and a dark pronotum. It can be distinguished from southern mole cricket by dactyl form. The tibial dactyls are nearly touching at the base, separated by less than half the basal width of a dactyl. Tawny mole cricket produces a loud, nasal trill at about 130 pulses per second during the first 90 minutes after sunset. (See color figure 160.)
Summaries of mole cricket life history were given by Worsham and Reed (1912), Thomas (1928), Hayslip (1943), and Walker (1984), though biology of short-winged mole cricket is poorly documented. Keys to North American and Caribbean area mole crickets were provided by Nickle and Castner (1984).
The crickets usually damage seedlings, feeding above-ground on foliage or stem tissue, and below-ground on roots and tubers. Girdling of the stems of seedling plants at the soil surface is a common form of injury, though young plants are sometimes severed and pulled below-ground to be consumed. Additional
injury to small plants is caused by soil surface tunneling, which may dislodge seedlings. Southern mole cricket does much more tunneling injury than tawny mole cricket.
Cultural Practices. Most injury to vegetable transplants occurs on small plants, so placement of larger plants is suggested as a strategy to avoid injury (Schuster and Price, 1992). Crickets can quickly invade crop land that has been fumigated or otherwise cleared of crickets, so isolation from sources of crickets, or planting in large blocks of land with proportionally little edge, is desirable (Poe, 1976).
Host-Plant Resistance. Efforts have been made to find turf and pasture grass varieties that are resistant to attack by mole crickets. If grass varieties contain antibiotic properties, or otherwise limit the reproductive abilities of mole crickets, this can translate into fewer crickets seeking food within vegetable crops, because grass-containing fields are a principal source of mole crickets. Thus far, strains have been identified which are fairly tolerant of feeding or which are not preferred by mole crickets, primarily the finer textured grass selections, but considerable improvement in these grasses is needed before they can affect cricket population biology.
Biological Control. Biological control of mole crickets can be enhanced by the application of the entomopathogenic nematode Steinernema carpocapsae. This nematode can be cultured and applied in the same manner as an insecticide, and is fairly persistent. It is more effective when applied to adults than applied to nymphs.
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