Xestia adela Franclemont Xestia dolosa Franclemont Lepidoptera Noctuidae

Natural History

Distribution. These species have long been known as Xestia (Amathes) c-nigrum (Linnaeus), a Eurasian species. However, they now have been differentiated into two other species: Xestia adela and Xestia dolosa (Fran-clemont, 1980). Xestia adela occurs throughout Canada and the United States, including Alaska, whereas X. dolosa occurs only in the eastern United States and Canada west to about North Dakota. They remain difficult to differentiate and are best treated together. Hudson (1982) suggested that these species are derived from separate introductions of X. c-nigrum.

Host Plants. Spotted cutworm is a general feeder, consuming various flowers, vegetables, fruit trees, and other plants. Among vegetables attacked are asparagus, beet, cabbage, carrot, cauliflower, celery, corn, lettuce, onion, pea, potato, rhubarb, tomato, and turnip. Fruits consumed include apple, cranberry, currant, gooseberry, raspberry, and pear. Occasional damage is incurred by barley, clover, flax, oat, rye, sugarbeet, tobacco, and wheat. Various weeds are consumed, including Canada thistle, Cirsium arvense; chickweed, Stellaria sp.; goldenrod, Solidago sp.; lambs-quarters, Chenopodium album; morningglory, Ipomoea sp.; redroot pigweed, Amaranthus retroflexus; smart-weed, Persicaria sp.; sunflower, Helianthus sp.; ferns and grasses.

Natural Enemies. Flies known to parasitize spotted cutworm include Euphorocera claripennis (Macquart), Winthemia quadripustulata (Fabricius), and W. rufopicta (Bigot) (all Diptera: Tachinidae). Among the wasp parasitoids of spotted cutworm are Apanteles yakutatonsis Ashmead (Hymenoptera: Braconidae), Eutanyacra succincta (Brulle) (Hymenoptera: Ichneu-monidae), Dibrachys carus (Walker) (Hymenoptera: Pteromalidae), and Euplectrus frontalis Howard (Hymenoptera: Eucharitidae).

Life Cycle and Description. The number of generations is variable. There reportedly are three generations annually in Tennessee, with moths present in April-May, July, and September-October (Crumb, 1929), though evidence for the middle generation is weak. In Washington, two flight generally are observed, but a small third flight late in the year is possible (Howell, 1979). In New York, Minnesota, and elsewhere, flights of moths occur in June-July and in August-October (Chapman and Lienk, 1981; Knutson, 1944); this seems to be the most common pattern of occurrence. Overwintering occurs in the larval stage, with pupation in early spring. Most damage to crops results from feeding by larvae of the summer generation, which normally pupate in August.

  1. The eggs are normally deposited on the underside of foliage. They are pinkish, and in shape resemble a slightly flattened sphere. They measure 0.60-0.65 mm in diameter and 0.50-0.61 mm in height. Eggs bear about 30 ridges, of which about 13-14 extend from the base to the center; the remainder terminate before they reach the top. They reportedly are deposited singly, in rows, or in clusters of up to 200 eggs. Duration of the egg stage is 6-12 days.
  2. Spotted cutworm displays seven instars. Head capsule widths are about 0.35, 0.55, 0.8, 1.3, 1.7, 2.1, and 3.0 mm for instars 1-7, respectively. Body length is about 2-4, 6, 0.9-1.5, 12-16, 14-20, 28, and

30-36 mm, respectively. The general body color is brown or gray, and it lacks distinct stripes. The most diagnostic character is a series of subdorsal triangles or wedges along the length of the body. The triangles are distinct posteriorly, but decrease in size toward the head. The head is light brown with dark markings. Duration of the larval stage in the winter period is 5-6 months, whereas it is only about one month during the summer. The larvae of X. adela and X. dolosa are structurally indistinguishable. However, X. dolosa has a longer developmental period and attains a greater size at larval maturity. When X. dolosa is reared at 24° C, the larval, pupal, and egg-adult periods were 27.6,15.8, and 43.3 days, respectively. In contrast, the corresponding periods were 21.0,12.1, and 32.4 days for X. adela. Maximum larval weights when reared at 24°C were 0.99 g for X. dolosa but only 0.56 g for X. adela. Not surprisingly, head capsule widths of X. dolosa tend to be slightly larger than X. adela. Although head size is about the same for both species through instar four, the widths are about 1.8 and 1.7mm in instar five, and 3.0 and 2.4 in instar six for X. dolosa and X. adela, respectively (Hudson, 1983). Larvae of all ages are prone to climb, but older larvae climb and feed only at night, dropping to the ground and seeking shelter during the daylight hours (Olson and Rings, 1969). (See color figure 58.)

Pupa. Pupation occurs in the soil. The pupa is about 18 mm long and 6 mm wide. It is brown. Duration of the pupal stage is 17-41 days.

Spotted cutworm larva.

Spotted cutworm larva.

Adult. The adult is a medium-sized moth, measuring 29-43 mm in wingspan. The moth of X. dolosa, which has a wingspan of 37-43 mm, is slightly larger than X. adela, with a wingspan of 29-38 mm. The front wings are purplish or reddish brown, with dark brown to black basally. At about the mid-point of the leading edge of the forewing is a light brown or tan-colored triangle. On average, X. adela tends to be slightly darker than X. dolosa. The hind wings are white to light gray, often darker along the outer margin. Moths of X. dolosa and X. adela fly at about the same periods each year. However, as might be expected from the longer developmental period of X. dolosa, the flight period of this species begins at a slightly later date than X. adela. Adults live 2-3 weeks in the field. (See color figure 248.)

These species are poorly known. Crumb (1929) gave the most complete account, but Howell (1979) provided valuable data from the west coast. Hudson

(1982) supplied developmental data. Franclemont (1980) and Hudson (1982) clarified the status of the North American species comprising dingy cutworm. Rings and Johnson (1977) published a bibliography. Spotted cutworm larvae were included in keys by Whelan (1935), Crumb (1956), Rings (1977b), Capinera (1986), and are included in a key to armyworms and cutworms in Appendix A. Moths were included in keys by Rings (1977a) and Capinera and Schaefer

Damage

Damage to crops results from feeding by both the overwintering larvae in the spring, and from the summer generation later in the growing season. The overwintering larvae are perhaps best known for their damage to fruit, because larvae readily climb vines and trees to feed on buds during the spring months, when vegetation is scarce. Although the larvae can sever young plants at ground level, they also feed on foliage and burrow into tomato fruits. At high densities larvae may assume a gregarious, dispersive "army-worm" habit. Spotted cutworm has been reported to be an early season rangeland pest, destroying nearly

Spotted Cutworms
Adult spotted cutworm.

all forbs and grasses in some areas (Launchbaugh and Owensby, 1982).

Management

  1. Light traps can be used to monitor populations of adults. A pheromone-based lure has also been identified, though it is not completely specific (Landolt, 2000). Although these are considered to be climbing cutworms, and larvae spend a good deal of time searching or feeding on foliar tissue, they also hide beneath plant debris and beneath the soil surface. Thus, it is important to rake the surface of the soil to search for larvae if cutworm injury is suspected.
  2. Insecticides are commonly used to control cutworms. Application of persistent insecticides to the base of the plant can be effective, as can foliar treatment of leafy vegetables. Bran and other organic baits treated with insecticide are effective methods of cutworm suppression. Bacillus thuringien-sis is not usually recommended for this pest.

Cultural Practices. Barriers have been used to prevent access by cutworms to buds and foliar tissues (Wright and Cone, 1983b), but in commercial crop production this has more applicability to perennial crops such as fruit than to annual crops such as vegetables. In the home garden, however, transplanted plants can be protected by a barrier such as a can or waxed paper container with the bottom removed. Aluminum foil wrapped around the base of the seedling also deters cutting by larvae. Ditches with steep sides and metal barriers can be effective impediments to prevent dispersal of cutworm larvae into crops.

Cutworm problems often develop in weedy fields or portions of fields infested with weeds. It is advisable to till, or otherwise destroy weeds, 10-14 days in advance of planting, as this should cause small larvae to starve. If seedlings are to be transplanted into a field or garden, larger plants are preferred because they are less likely to be irreparably damaged by cutworms.

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