Agrotis subterranea Fabricius Lepidoptera Noctuidae

Natural History

Distribution. This species is native to the western hemisphere, and principally tropical in distribution. Although occasionally found as far north as Nova Scotia and Minnesota, it appears not to breed at these latitudes, and is not known from the northwestern states. It is common south of the Ohio River and regularly damaging in the southernmost states from Georgia to California. It also occurs in Central and South America and the Caribbean.

Host Plants. Granulate cutworm feeds on a wide range of plants. Among vegetables attacked are bean, beet, broccoli, Brussels sprouts, cabbage, carrot, cauliflower, celery, corn, cowpea, eggplant, kale, lettuce, onion, pea, pepper, potato, radish, spinach, sweet potato, tomato, turnip, and watermelon. Other crops reported injured include alfalfa, clover, cotton, lespe-deza, peach, peanut, sorghum, soybean, strawberry, tobacco, vetch, and wheat. Some of the weeds observed to support larvae include thorny amaranth, Amaranthus spinosus; cocklebur, Xanthium sp.; dandelion, Taraxacum sp.; passion vine, Passiflora incarnata; plantain, Plantago sp.; and shepherdspurse, Capsella bursa-pastoris.

Natural Enemies. Considering the importance of this cutworm in southern states, surprisingly little is known about natural enemies. Among the wasps known to parasitize granulate cutworm are Apanteles griffini Viereck, Chelonus insularis Cresson, Meteorus laeventris (Wesmael), M. laphygmae Viereck, Microga-sterfeltiae Meusebeck, Zele mellea (Cresson) (all Hyme-noptera: Braconidae), Campoletis flavicincta (Ashmead) and Simphion merdarius (Gravenhorst) (both Hyme-noptera: Ichneumonidae). Fly parasitoids known from this cutworm include Bonnetia comta (Fallen), Gonia crassicornis (Fabricius), G. longipulvilli Tothill, Lespesia archippovora (Riley), and Spallanzania hebes (Fallen) (all Diptera: Tachinidae). A microsporidian disease was reported from Florida (Adlerz, 1975) and a gran-ulosis virus is known (Hamm and Lynch, 1982), but the importance of natural pathogens is uncertain.

Life Cycle and Description. Granulate cutworm is active continuously in the south; adults, eggs and larvae have been collected during all months in Louisiana. Nevertheless, there seems to be seasonality to reproduction, as unmated females are found mostly from May-November. Total abundance similarly is greatest in June-November. In Tennessee, three complete generations are reported, with overwintering insects emerging in March. In addition to egg production about March, peaks in egg production occur in May, July and September. The pupae from the September generation overwinter. The complete life cycle requires 50-70 days.

  1. The eggs are deposited singly or in small clusters on the upper surface of foliage. Females produce about 800-1600 eggs. They are hemispherical, with 36-40 narrow ridges radiating from the apex, and measure 0.60-0.71 mm in diameter and about 0.50 mm in height. Initially they are white, but darken with age. Normally they hatch in 3-5 days.
  2. Young larvae initially remain on the foliage during both day and night, but after a few days they begin to hide beneath plant debris or soil during the daylight hours, feeding only at night. The larva buries itself very shallowly, even remaining partially exposed during the day. The number of instars varies from 5-7, but six instars is most common. Mean (range) head capsule widths are 0.31 (0.30-0.32), 0.48 (0.45-0.50), 0.81 (0.73-0.86), 1.31 (1.17-1.57), 1.98 (1.62-2.26), and 2.93 (2.70-3.19) mm for instars 1-6, respectively. Mean (range) duration of the instars is 3.4 (3-5), 2.5 (2-4), 3.1 (3-4), 3.1 (2-5), 4.8 (3-7), and 7.7 (5-10) days, respectively. Total larval development time is about 25 days for larvae with six instars, but 22 days for five-instar larvae and 32 days for seven-instar larvae. The body length measures about 2.0-3.5, 5-6, 12, 17, 22, and 30-37mm long during instars 1-6, respectively. Larvae with six instars consume about 150 sq cm of foliage but the longer-lived larvae that undergo seven instars consume considerably more, up to 240 sq cm. This cutworm is grayish to reddish brown, with each abdominal segment bearing dull yellowish oblique marks subdorsally. A weak gray line occurs laterally below the spiracles, accompanied by spots of white or yellow. The head is yellowish to brownish. (See color figure 53.)
  3. Pupation occurs in the soil, usually at a depth of 3-12 cm. The pupae are dark brown or mahogany, and measure 15-21 mm long and 5-6 mm wide. Duration of the pupal stage is 10-20 days.
  4. Moths begin mating about one day after emergence, and peak oviposition occurs 2-3 nights

Granulate cutworm larva.

Granulate cutworm larva.

after mating (Cline and Habeck, 1977). Longevity of adults is 10-20 days, averaging about 14 days. The moth is medium in size, with a wingspan of 3143 mm. The color of the forewing varies considerably in its shades of brown and gray, but it is often yellowish-brown and distinctly lighter distally. The forewing bears distinct bean-shaped and round spots centrally, and these spots are linked by a small but sharply defined black bar. The hind wings are white, but dusky marginally and along the veins. (See color figures 242 and 243.)

Biology was described by Jones (1918b), and Snow and Callahan (1968), with the most complete morphological description by Crumb (1929). Culture techniques were described by Lee and Bass (1969). Keys including the larva of this species were given by Crumb (1929, 1956), Whelan (1935), Okumura (1962), Oliver and Chapin (1981), and in a key to armyworms and cutworms in Appendix A. The moth was included in a pictorial key by Capinera and Schaefer (1983).

Damage

This is the most important cutworm pest of vegetables in the Gulf Coast region, and also quite important in California. It damages seedlings by cutting off the stem at the soil surface, older plants by climbing and feeding on foliage, and injures such plants as tomato, watermelon, and eggplant by feeding on, or burrowing into, the fruit. Due to its surface-feeding behavior, granulate cutworm is sometimes a major component of the "rindworm" complex affecting cucurbit fruit. This type of damage usually occurs when fruit are in contact with soil, a common habitat of the larva. Young larvae, through about the second instar, feed on the lower leaf surface and skeletonize leaves. Thereafter, they consume entire leaves.

Management

Moth populations can be monitored with blacklight traps. Larvae can be controlled by application of insec-

Agrotis Subterranea
Adult granulate cutworm.

ticides delivered as liquid, granule, or bait formulation. Baits, particularly bran-based, seem particularly effective (Morgan and French, 1971). Bacillus thurin-giensis is not usually recommended for cutworms. Many cutworm species have a great affinity for weedy fields, but granulate cutworm seems to lack this association. Mechanical barriers can provide some protection from dispersing larvae to seedlings in the home garden. However, moths often are active during the growing season and easily circumvent such barriers. Therefore, it may also be necessary to use netting or row cover material to deny access to plants by ovipositing moths.

0 0

Post a comment