Distribution. Field crickets are extremely difficult to distinguish based on appearance, so for many years they have been grouped into one species, Gryllus assimilis (Fabricius). As the significance of the calling behavior (chirping) became known, some of the species have been distinguished, but much work remains. The biology and damage potential of the various field crickets is confused by the problems with identification. The most economically significant North American species are fall field cricket, Gryllus pennsylvanicus Burmeister; spring field cricket, Gryllus veletis (Alexander and Bigelow); and southeastern field cricket, Gryllus rubens Scudder; though other species may be locally important. The fall and spring field crickets are most abundant in the northern states and southern Canada, whereas the southeastern field cricket is known from the southeastern states. These are native insects.
Host Plants. These field crickets are found widely in grassy fields, pastures, weedy areas, roadsides and lawns, and occasionally feed on foliage, flowers and fruit of crop plants. Among the vegetable crops damaged are bean, beet, carrot, cabbage, cantaloupe, cucumber, lettuce, parsnip, pea, potato, pumpkin, squash, sweet potato, tomato, watermelon, and likely others. Other crops known to be injured by field crickets are alfalfa, barley, corn, cotton, flax, rye, strawberry, sweetclover, and wheat. Flowers and seeds of weeds also are suitable food for crickets, and among those known to be consumed are foxtail, Setaria spp.; lambsquarters, Chenopodium album; pigweed, Amar-anthus spp.; ragweed, Ambrosia spp.; Russian thistle, Salsola kali; sunflower, Helianthus spp.; and wheat-grass, Agropyron spp. Russian thistle is reported to be particularly suitable, and foliage as well as flowers and seeds are eaten. The foliage of broadleaf plants is preferred over grasses.
Natural Enemies. Many natural enemies of field crickets are known, though their importance is poorly documented. Eggs are parasitized by Ceratotelia mar-lattii Ashmead and Paridris brevipennis Fouts (both Hymenoptera: Scelionidae), with 20-50% of the eggs in South Dakota reportedly parasitized by C. marlatti and 1-5% by P. brevipennis. Nymphs and adults are killed by Exoristoides johnsoni Coquillett and Euphasiop-teryx ochracea (Bigot) (both Diptera: Tachinidae), Sar-cophaga kelleyi Aldrich (Diptera: Sarcophagidae), mermithid nematodes (Nematoda: Mermithidae), and horsehair worms (Nematomorpha). Gregarine parasites (Sporozoa) infest the guts of field crickets (Zuk, 1987), but have little effect on their host other than to extend the cricket developmental period. Among the predators that take advantage of cricket abundance are many birds, but particularly crows, Corvus bachyrhynchos brachyrhynchos Grehm; and ring-necked pheasant, Phasianthus torquatus Gmelin; as well as snakes, toads, and gophers.
Life Cycle and Description. Field crickets differ in their life history, but the aforementioned species exemplify the common life cycles. Gryllus pennsylvanicus and G. veletis have one generation per year, whereas G. rubens has two generations annually. In South Dakota and most of its range, G. pennsylvanicus eggs overwinter, hatching occurs in the spring, nymphs develop in early summer, adults appear beginning in July, and eggs are deposited in August and September. The presence of adults in the late summer and autumn is the basis for its common name of "fall" field cricket. In Michigan, adults chirp from early August until mid-November (Alexander and Meral, 1967).
In the same area, G. veletis nymphs overwinter in the later instars, the adult stage is attained in May-June, eggs are produced in May-June, hatching is completed by the end of August, and nymphs complete part of their development before the onset of winter.
The presence of adults during spring and early summer is the basis for its common name of "spring" field cricket. In Michigan, adults chirp from mid-May until early August. Thus, though these two field cricket species occupy the same habitat, there is seasonal separation of life stages.
In Louisiana and most of its range, G. rubens overwinters as nymphs, the adult stage is attained by April when eggs are produced, and nymphs are mature by July. Second generation adults begin to appear and produce eggs in late July-August, and nymphs develop until winter, failing to molt to the adult stage until the subsequent spring.
Egg. Eggs are deposited in firm, damp soil, usually within the upper 2 cm of soil. Under dry conditions crickets may deposit their eggs within the cracks formed as moist soil hardens. The eggs are elongate-cylindrical, with bluntly rounded ends. They also are slightly curved, with one side convex and the opposite side concave. Eggs normally measure about
3 mm long and 0.6 mm wide. They are light yellow or cream. As the embryo develops it may change shape and color, and increase slightly in size. Such eggs become barrel-shaped, and measure about
4 mm long and 0.85 mm wide. They are deposited singly, but several are usually placed in close proximity. The number of eggs produced by each female ranges from about 150-400. Except for overwintering eggs, most hatch in about two weeks.
Nymph. The young cricket hatching from an egg is faced with the difficult task of burrowing through soil to reach the surface. The form of the cricket that escapes the egg is called the "vermiform larva," and differs from the following nymphal stages by being encased in a transparent membrane that immobilizes the appendages. Once the vermiform larva wriggles to the surface the membrane is shed, the legs are freed, and the young first instar cricket is able to walk and jump. The cricket undergoes several molts, growing at each stage. In G. pennsylvanicus and G. veletis normally there are 8-9 instars, though there may be more under adverse conditions. Mean duration of instars under field temperature in South Dakota was reported to average about 8.5, 8.2, 8.9, 8.8, 9.3, 10.7, 11.9, 12.0, and 14.6 days for instars 1-9, respectively. In G. rubens the number of instars averages 10, but the same pattern of latter instars requiring more time for development is apparent. Total nymphal development time usually requires 80-90 days in the cooler northern environments inhabited by G. pennsylvanicus and G. veletis, and 70-80 days in the warmer environments inhabited by G. rubens.
The nymphs initially are brownish, but marked with black and sometimes yellow in the thoracic area. They resemble the adults, and bear long antennae and cerci, but lack wings. With each succeeding molt the nymphs become darker. The ovipositor begins to appear in instars 3-4, the wing pads in instar six. By instar eight both the ovipositor and wing pads are apparent. Body length is about 3, 3.3-3.9, 4.2-5.0, 56, 7-8, 7.3-8.5, 9-12,12-18, and 13.5-20 mm for instars 1-9, respectively.
Adult. The adult cricket is mostly shiny black, though the front wings may be brownish-black. The front wings usually cover the abdomen or extend slightly beyond the tip. The hind wings, however, are variable long, and wing length determination has both environmental and genetic components (Walker, 1987). In short-winged forms at least half of the abdomen is covered, but such insects are incapable of flight. Long-winged forms tend to be a small component of the population (Veazey et al., 1976; Harrison, 1979), and though they are capable of flight, they do not often fly (Walker and Sivinski, 1986; Walker, 1987). Body length of adults is 15-26 mm. Females bear a long ovipositor, which often equals the length of her body. The width of the head is greater than the pronotum in G. pennsylvanicus and G. veletis, whereas in G. rubens the head is narrower than the pronotum. Males of these cricket ordinarily space themselves in a field and remain rather sedentary for all of their adult lives. They produce a song that attracts roving females. The song of G. pennsylvanicus and G. veletis is intermittent, which consists of about 150-240 discrete chirps per minute at 29°C, with chirps comprised of four pulses at about 25 pulses per second. In contrast, G. rubens produces a nearly continuous song, consisting of about 60 pulses per second at 29°C, with a considerably louder song than the other species. Females usually mate within 1-4 days of attaining the adult stage, and normally they mate repeatedly during the oviposition period. Most females commence oviposi-tion from 7 to 14 days after attaining the adult stage, though some require up to 30 days. Egg production continues for the life of the cricket, with 50-60 days considered to be about average adult longevity.
Crickets are usually active at night, though they may venture forth during daylight during cloudy weather, and in late afternoon. Males normally call at night, but in cold weather may call during warmer daylight hours. Typically, crickets hide beneath debris during the day, but sometimes seek shelter in soil cracks or excavate small chambers in the soil. They sometimes appear to be gregarious, because they are found clustered, but this is simply a reflection of preference for a habitat with limited availability.
Alexander (1957) discussed the taxonomy of eastern field crickets and included keys to separate most species based on morphology; however, the fall and spring field crickets were treated as spring and fall broods of "pennsylvanicus.'' Nickle and Walker (1974) provided keys to the southeastern species. An excellent treatment of fall and spring field cricket biology (as G. assimilis) was provided by Severin (1935), with similar treatment of (probably) G. rubens (as G. assimilis) by Folsom and Woke (1939). Calling behavior of G. pennsylvanicus and G. veletis was described by Alexander and Meral (1967), and of G. rubens by Doherty and Callos (1991). Synopses of fall and spring field crickets, including keys to related Canadian Orthoptera, were given by Vickery and Kevan (1985). Culture of field crickets was described by Winewriter and Walker (1988).
Field crickets are omnivorous, and feed on a variety of plant and animal matter. They may consume the roots, stems, leaves, flowers, fruits and seeds of plants, but the flower, fruit and developing seeds are preferred. Once mature, seeds are no longer suitable. They also eat nearly any dead insect they encounter, sometimes are reported to be cannibalistic, and gnaw on animal and plant products such as fur, wool, linen, and cotton. They are rarely considered to be serious plant pests, and only when exceedingly abundant. Spring field cricket, in particular, is questionable as a plant pest, because it is not very gregarious.
Field crickets also display predatory behavior which offsets their occasional tendency to feed on valuable plants. For example, grasshopper eggs, flea
beetle adults, fly puparia, caterpillar pupae, and insects from spider webs are among the documented animal material eaten by nymphs and adults (Burgess and Hinks, 1987).
Suppression of crickets is rarely necessary, but application of insecticide-treated bran bait is effective if needed. Often its application can be limited to the edge of fields, where crickets dispersing into crops would encounter and ingest the poison bait. A formula for preparing baits was given by Severin (1935), but modern bait formulations usually eliminate molasses and other additives, employing only coarse bran and insecticide. Insecticides can also be applied to sawdust and distributed broadcast or in a band around the margin of a field; in such cases crickets perish from contact rather than ingestion of the bait, and this approach is most appropriate when cricket densities are very high (Blank et al., 1985). Foliar applications of insecticides can also be effective if they are residual, but are less selective. Soil tillage can destroy eggs, and clean cultivation deprives overwintering insects of shelter.
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