Distribution. Black cutworm is found widely around the globe, though it is absent from some tropical regions and cold areas. Its origin is uncertain. It is more widespread, and damaging, in the northern than the southern hemispheres. It is found annually throughout the United States and southern Canada, but apparently does not overwinter in northern states and Canada. There is strong evidence that black cutworm disperses northward from the Gulf Coast region each spring.
Long distance dispersal of adults has long been suspected in Europe, China, and North America. The basic pattern is to move north in the spring, and south in the autumn. Studies in the United States demonstrated northward displacement of moths during the spring in the range of 1000 km in 2-4 days when assisted by northward flowing air (Kaster and Showers, 1982; Showers et al., 1989; Smelser et al., 1991). Similar displacement to the south and southwest has been documented in the autumn (Showers et al., 1993).
Host Plants. Black cutworm has a wide host range. Among vegetables injured are artichoke, asparagus, bean, beet, broccoli, cabbage, cantaloupe, carrot, cauliflower, celery, Chinese cabbage, corn, cowpea, cucumber, eggplant, garbanzo, garlic, kale, kohlrabi, lettuce, mustard, okra, onion, pea, pepper, potato, sweet potato, radish, spinach, squash, tomato, turnip, and watermelon. This species also feeds on alfalfa, clover, cotton, rice, sorghum, strawberry, sugarbeet, tobacco, and sometimes grains and grasses. Suitability of several grasses and weeds for larval development was studied by Busching and Turpin (1977); among the relatively suitable plants were bluegrass, Poa pra-tensis; curled dock, Rumex crispus; lambsquarters, Che-nopodium album; yellow rocket, Barbarea vulgaris; and redroot pigweed, Amaranthus retroflexus. The preference by black cutworm for weeds is sometimes quite pronounced. Genung (1959), for example, demonstrated how black cutworm, the dominant cutworm species in southern Florida during the winter, would avoid feeding on beans if spiny amaranth, Amaranthus spinosus, was present. Adults feed on nectar from flowers. Deciduous trees and shrub such as linden, wild plum, crabapple, and lilac are especially attractive to moths (Wynne et al., 1991).
Natural Enemies. Numerous species of natural enemies have been associated with black cutworm, but data on their relative importance are scarce. However, Puttler and Thewke (1970) collected black cutworm larvae in Missouri and reported 69% parasitism, so natural enemies probably exact a significant toll on cutworm populations. Among the wasps known to attack this cutworm are Cotesia marginiven-tris (Cresson), Microplitis feltiae Muesebeck, Microplitis kewleyi Muesebeck, Meteorus autographae Muesebeck, Meterorus leviventris (Wesmael) (all Hymenoptera: Bra-conidae); Campoletis argentifrons (Cresson), Campoletis flavicincta (Ashmead), Hyposoter annulipes (Cresson), and Ophion flavidus Brulle (all Hymenoptera: Ichneu-monidae). Larvae parasitized by Meteorus leviventris (Wesmael) consume about 24% less foliage and cut about 36% fewer seedlings (Schoenbohm and Turpin, 1977), so considerable benefit is derived from parasitism in addition to the eventual death of the host larva. Other parasitoids known from black cutworm include flies often associated with other ground-dwelling noc-tuids, including Archytas cirphis Curran, Bonnetia comta (Fallen), Carcelia formosa (Aldrich and Webber), Chaeto-gaedia monticola (Bigot), Eucelatoria armigera (Coquil-lett), Euphorocera claripennis (Macquart), Gonia longipulvilli Tothill, G. sequax Williston, Lespesia archip-pivora (Riley), Madremyia saundersii (Williston), Sisyr-opa eudryae (Townsend), and Tachinomyia panaetius (Walker) (all Diptera: Tachinidae). Predatory ground-dwelling insects such as ground beetles (Coleoptera: Carabidae) apparently consume numerous larvae (Best and Beegle, 1977; Lund and Turpin, 1977). Although Genung (1959) indicated that 75-80% of cutworms could be killed by a granulosis virus, there is surprisingly little information on epidemiology and of natural pathogens. Rather, such pathogens as viruses, fungi, bacteria, and protozoa from other insects have been evaluated for black cutworm susceptibility; in most cases only relatively weak pathogens have been identified (Ignoffo and Garcia, 1979; Grundler et al., 1987; Johnson and Lewis, 1982a,b). An entomopa-thogenic nematode, Hexamermis arvalis (Nematoda: Mermithidae), is known to parasitize up to 60% of larvae in the midwestern states (Puttler and Thewke, 1971; Puttler et al., 1973).
Life Cycle and Description. The number of generations occurring annually varies from 1-2 in Canada to 2-4 in the United States. In Tennessee, moths are present in March-May, June-July, July-August, and September-December. Based on light trap collections, moths are reported to be abundant in Arkansas during May-June and September-October (Selman and Barton, 1972), and in New York they occur mostly in June-July (Chapman and Lienk, 1981). However, light traps are not very effective during the spring flight, and underestimate early season densities (Willson et al., 1981; Levine et al., 1982). Thus, the phenology of black cutworm remains uncertain, or perhaps is inherently variable owing to the vagaries associated with long-range dispersal. Overwintering has been reported to occur in the pupal stage in most areas where overwintering occurs, but larvae persist throughout the winter in Florida. Pupae have been known to overwinter as far north as Tennessee, but apparently are incapable of surviving farther north (Story and Keaster, 1982a). Thus, moths collected in the midwestern states in March and April are principally dispersing individuals that are past their peak egg production period (Clement et al., 1985). Nonetheless, they inoculate the area and allow production of additional generations, including moths which disperse north into Canada. Duration of the life cycle is normally 35-60 days.
In appearance, the larva is rather uniformly colored on the dorsal and lateral surfaces, ranging from light gray or gray-brown to nearly black. On some individuals, the dorsal region is slightly lighter or brownish, but the larva lacks a distinct dorsal band. Ventrally, the larva tends to be lighter in color. Close examination of the larval epidermis reveals that this species
Black cutworm larva.
bears numerous dark, coarse granules over most of its body. The head is brownish with numerous dark spots. Larvae usually remain on the plant until the fourth instar, when they become photonegative and hide in the soil during the daylight hours. In these latter instars they also tend to sever plants at the soil surface, pulling the plant tissue below-ground. Larvae tend to be cannibalistic. (See color figure 43.)
The life cycle of black cutworm was described by Harris et al. (1962b) and Abdel-Gawaad and El-Shazli (1971). Developmental data were provided by Satterthwait (1933), Luckmann et al. (1976), Archer et al. (1980), and Beck (1988). Laboratory culture on artificial media has been described (Reese et al., 1972; Blenk et al., 1985). Rings et al. (1974b) published a bibliography. The larva was described, and included in a key, by Crumb (1929, 1956). Larvae are also included in keys published by Okumura (1962), Rings (1977b), Oliver and Chapman (1981), and Capinera (1986), and is included in a key to armyworms and cutworms in Appendix A. Moths are included in keys of Rings (1977a) and Capinera and Schaefer (1983).
This species occurs frequently in many crops, and is one of the best-known cutworms. Despite the frequency of occurrence, however, it tends not to appear in great abundance, as is known in some other cutworms and armyworms. Black cutworm is not consid-
ered to be a climbing cutworm, most of the feeding occurring at soil level. However, larvae will feed above-ground until about the fourth instar. Larvae can consume over 400 sq cm of foliage during their development, but over 80% occurs during the terminal instar, and about 10% in the instar immediately preceding the last (Satterthwait, 1933). Thus, little foliage loss is possible during the early stages of development. Once the fourth instar is attained, larvae can do considerable damage by severing young plants, and a larva may cut several plants in a single night. Plants tend to outgrow their susceptibility to injury. Showers et al. (1983) demonstrated that corn at the one-leaf stage was very susceptible to damage, but that by the four- or five-leaf stage plant yield was not decreased by larval feeding. Levine et al. (1983) showed that leaf feeding and cutting above the soil line were less damaging to corn than cutting at the soil surface, and that subterranean damage was very injurious.
Sampling. Adult populations can be monitored with both blacklight and sex pheromone traps. However, several authors have noted the inefficiency of light traps. Light traps are relatively effective in the summer and autumn, but the late-season generations generally pose little threat to crops. Pheromone traps are more effective during the spring flight, when larvae present the greatest threat to young plants (Will-son et al., 1981). Trap color affects moth capture rate, with white and yellow traps capturing more than green traps (Hendrix and Showers, 1990).
Large larvae burrow in the soil, and are difficult to observe. However, larvae can be sampled with bait traps, and this is most effective before emergence or planting of seedlings. Various trap designs have been studied, but many employ a container sunk into the soil with the upper lip at the soil surface. The container is baited with fresh plant material and/or bran, and with vermiculite so that the larvae can attain shelter. Larvae are effectively captured in baited containers if the vermiculite is not very near the surface (Story and
Keaster, 1983), and catches are enhanced if a screen cylinder, which provides a visual stimulus to the cutworms, is suspended above the baited container (Whitford and Showers, 1984). If plants are present in the field they compete with the bait in the traps, and trap efficiency declines markedly. The distribution of larvae in the spring is random (Story and Keaster, 1982b).
Insecticides. Persistent insecticides are commonly applied to plants and soil for black cutworm suppression, but surface rather than subsurface soil applications are desirable (Foster et al., 1990). Larvae readily accept insecticide-treated bran and other baits (Sech-riest and Sherrod, 1977; Gholson and Showers, 1979). Application of systemic insecticides to seeds also provides some protection against larval injury (Levine and Felsot, 1985; Berry and Knake, 1987). Bacillus thuringiensis is not usually recommended for cutworm control.
Cultural Practices. Black cutworm larvae feed readily on weeds, and destruction of weeds can force larvae to feed exclusively on crop plants, exacerbating damage. Thus, it is often recommended that weeds not be tilled or treated with herbicide until larvae are matured. Timing is important, however, because prolonged competition between crop and weed plants can reduce crop yield (Engelken et al., 1990). Presence of flowering weeds also can be beneficial by supporting prolonged survival of parasitoids (Foster and Ruesink, 1984). In contrast, reduced tillage cropping practices, which often produce higher weed populations, seem to result in increased abundance of black cutworm and higher levels of cutting in corn (Johnson et al., 1984; Tonhasca and Stinner, 1991; Willson and Eisley, 1992). This may be due, in part, to the tendency of moths to oviposit on weeds; weedy fields tend to have higher cutworm populations (Sherrod et al., 1979).
Black cutworm populations also tend to be higher in wet areas of fields, and in fields that are flooded. Black cutworm has been known, at times, as "overflow worm," due to its tendency to become abundant and damaging in fields that are flooded by overflowing rivers (Rockwood, 1925).
In the home garden, barriers are sometimes useful to prevent damage to seedlings by cutworms. Metal or waxed-paper containers with both the top and bottom removed can be placed around the plant stem to deter consumption. Aluminum foil can be wrapped around the stem to achieve a similar effect. As the larvae burrow and feed below the soil line it is necessary to extend to barrier below the soil surface. Because black cutworm moths, which easily circumvent such barriers, are active during the growing season; this procedure alone may have little value. Use of netting or row covers, in addition to larval barriers, can prove more effective.
Biological Control. Entomopathogenic nemato-des (Nematoda: Steinernematidae and Heterorhabditi-dae) will infect and kill black cutworm larvae, but their populations normally need to be supplemented to realize high levels of parasitism (Capinera et al., 1988; Levine and Oloumi-Sadeghi, 1992). Their effectiveness is related to soil moisture conditions (Baur et al., 1997).
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