Distribution. Tobacco budworm is a native species and is found throughout the eastern and southwestern United States. Like corn earworm, Helicoverpa zea (Bod-die), it generally overwinters successfully only in southern states. However, it occasionally survives in cold climates in greenhouses and other sheltered locations. Tobacco budworm disperses northward annually, and can be found in New England, New York, and southern Canada during the late summer. It also occurs widely in the Caribbean, and sporadically in Central and South America.
Host Plants. Tobacco budworm is principally a field-crop pest, attacking such crops as alfalfa, clover, cotton, flax, soybean, and tobacco. However, it some times attacks such vegetables as cabbage, cantaloupe, lettuce, pea, pepper, pigeon pea, squash, and tomato, especially when cotton or other favored crops are abundant. Tobacco budworm is a common pest of geranium and other flower crops such as ageratum, bird of paradise, chrysanthemum, gardenia, geranium, petunia, mallow, marigold, petunia, snapdragon, straw-flower, verbena, and zinnia. Weeds serving as a host for larvae include beardtongue, Penstemon laevigatus; beggarweed, Desmodium spp.; bicolor lespedeza, Lespe-deza bicolor; black medic, Medicago lupulina; cranesbill, Geranium dissectum; deergrass, Rhexia spp.; dock, Rumex spp., groundcherry, Physalis spp.; Japanese honeysuckle, Lonicera japonica; lupine, Lupinus spp.; morningglory, Ipomoea spp.; a morningglory, Jacque-montia tamnifolia; passionflower, Passiflora sp.; prickly sida, Sida spinosa; sunflower, Helianthus spp.; toadflax, Linaria canadensis; and velvetleaf, Abutilon theophrasti (Brazzel et al., 1953; Neunzig, 1963; Graham and Robertson, 1970; Roach, 1975; Harding, 1976a; Stadelbacher, 1981; Pair, 1994; Sudbrink and Grant, 1995). In Georgia, Barber (1937) determined that tobacco bud-worm developed principally on toadflax during April-May for 1-2 generations, followed by one generation on deergrass during June-July and 2-3 generations on beggarweed during July-October. In Mississippi, cranesbill was identified as the key early season host plant (Stadelbacher, 1981). In southern Texas, cotton is the principal host, but such weeds as wild tobacco, Nicotania repanda; vervain, Verbena neo-mexicana; ruellia, Ruellia runyonii; and mallow, Aubiti-lon trisulcatum, are important hosts early or late in the year (Graham et al., 1972). In cage tests and field studies conducted in Florida and which did not include cotton, tobacco was more highly preferred than other field crops and vegetables, but cabbage, collards, okra, and tomato were attacked (Martin et al., 1976a).
Natural Enemies. Numerous general predators have been observed to feed upon tobacco budworm. Among the most common are Polistes spp. wasps (Hymenoptera: Vespidae); big-eyed bug, Geocoris punc-tipes (Say) (Hemiptera: Lygaeidae); damsel bugs, Nabis spp. (Hemiptera: Nabidae); minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae), and spiders.
Several parasitoids also have been observed, and high levels of parasitism have been reported (Lewis and Brazzel, 1968; Tingle et al., 1994). The egg parasi-toid Trichogramma pretiosum Riley (Hymenoptera: Tri-chogrammatidae) can be effective in vegetable crops. Other important parasitoids are Cardiochiles nigriceps Viereck in vegetables and Cotesia marginiventris (Cresson) in other crops (both Hymenoptera: Braconidae). Effectiveness of the parasitoids varies among crops (Martin et al., 1981). Other species known from tobacco budworm include Archytas marmoratus (Townsend) (Diptera: Tachinidae); Meteorus autographae Muese-beck (Hymenoptera: Braconidae); Campoletis flavicincta (Ashmead), C. perdistinctus (Viereck), C. sonorensis (Cameron), Netelia sayi (Cushman) and Pristomerus spi-nator (Fabricius) (all Hymenoptera: Ichneumonidae).
Pathogens are also known to inflict mortality. Among the known pathogens are microsporidia, Nosema spp., fungi such as Spicaria rileyi, and nuclear polyhedrosis viruses. In a study conducted in South Carolina, Spicaria was a more important mortality agent than natural incidence of virus, and was considered to be one of the most important natural mortality agents (Roach, 1975).
Life Cycle and Description. Moths emerge during March-May in southern states, followed by 4-5 generations through the summer, with overwintering commencing in September-November. Four generations have been reported from northern Florida (Chamberlin and Tenhet, 1926) and North Carolina (Neunzig, 1969), and at least five from Louisiana (Brazzel et al., 1953). Moths have been collected in New York in July-September, but at such northern latitudes it is not considered to be a pest (Chapman and Lienk, 1981). This species overwinters in the pupal stage.
Tobacco budworm larva.
Tobacco budworm larva.
iod of females is about two-days long. Longevity of moths is reported to range from 25 days when held at 20°C, to 15 days at 30°C. A sex pheromone has been identified (Tumlinson et al., 1975).
The biology of tobacco budworm was given by Neunzig (1969) and Brazzel et al. (1953). The larva was included in keys by Okumura (1962) and Oliver and Chapin (1981); the latter publication also pictured the adult stage. Tobacco budworm also is included in a key to armyworms and cutworms in Appendix A. Larvae are readily cultured on bean-based rearing media or other diets (King and Hartley, 1985).
Larvae bore into buds and blossoms (the basis for the common name of this insect), and sometimes the tender terminal foliar growth, leaf petioles, and stalks. In the absence of reproductive tissue, larvae feed read-
ily on foliar tissue. Neunzig (1969) infested tobacco with both tobacco budworm and corn earworm, and observed very similar patterns and levels of injury by these closely related species. In California, both budworm and earworm burrow into the heads of developing lettuce. Entry of larvae into fruit increases frequency of plant disease. Research in southern Arkansas tomato fields indicated that though tobacco budworm was present from May-July, they were not nearly as abundant or damaging as corn earworm (Roltsch and Mayse, 1984).
Cultural Techniques. Early season destruction of weeds with herbicide or mowing, or destruction of larvae on the weeds by treatment with insecticides, can reduce tobacco budworm population size later in the year (Bell and Hayes, 1994; Snodgrass and Stadelbacher, 1994).
Biological Control. The microbial insecticide Bacillus thuringiensis is effective against budworm (Johnson, 1974; Stone and Sims, 1993). Heliothis nuclear polyhedrosis virus has been used effectively to suppress tobacco budworm on field crops (Andrews et al., 1975) and on early season weed hosts (Hayes and Bell, 1994). Tobacco budworm also is susceptible to nuclear polyhedrosis virus from alfalfa looper, Autographa californica (Speyer) (Vail et al., 1978; Bell and Romine, 1980). Release of Trichogramma egg parasitoids has been shown to be beneficial in some vegetable crops (Martin et al., 1976b).
Host-Plant Resistance. Although there is little evidence for natural resistance to tobacco budworm among many crops, cotton is being genetically engineered to express resistance (Benedict et al., 1996). Enhanced resistance to larval survival by cotton should result in lower insect pressure on nearby vegetable crops.
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