Autographa califomica Speyer Lepidoptera Noctuidae

Natural History

Distribution. Alfalfa looper is native to North America, and is western in distribution. In the United States it occurs occasionally in Nebraska and Kansas, and frequently in all states further west. It is most damaging along the West Coast. In Canada its distribution is similar, and is considered a pest only in British Columbia and Alberta. Alfalfa looper is also known from Mexico.

Host Plants. This insect feeds on numerous plants. Vegetable crops reportedly injured include beet, bean, cabbage, carrot, cantaloupe, celery, cucumber, lettuce, onion, pea, potato, radish, rhubarb, spinach, squash, tomato, turnip, watermelon, and probably others. The most frequently damaged vegetables are lettuce, bean, and the crucifer crops. Field crops damaged include alfalfa, cotton, red clover, sweet clover, flax, white clover, sugarbeet, and sunflower; as its common name suggests, alfalfa is the most common host. Grasses and grains are not eaten, with the exception of rare feeding on corn. Fruit crops such as apple, currant, gooseberry, raspberry may be damaged. Many of the hosts recorded in the literature are based on outbreak conditions, when hordes of larvae, after totally consuming their preferred hosts, disperse in search of food. Under such conditions, relatively unpreferred plants such as the aforementioned fruit crops may be eaten, but this is not the normal situation. Numerous common weeds support larval development, including dock, Rumex crispus.; lambsquarters, Chenopodium album; wild lettuce, Lactuca canadensis; and many others.

Natural Enemies. Mortality due to natural enemies was estimated at 70-80% in California (Puttaru-driah, 1953), of which parasitoids accounted for 3035% and the remaining from undetermined diseases. The principal parasitoid was Voria ruralis Fallen (Diptera: Tachinidae). Also present were Microplitis spp. and Apanteles yakutatensis Ashmead (Hymenoptera: Braconidae), and Campoletes sonorensis (Cameron) and Patroclides montanus (Cresson) (Hymenoptera: Ichneu-monidae). Other parasitoids, of uncertain importance, were noted by Hyslop (1912a). A nuclear polyhedrosis virus is very common in alfalfa looper populations, usually killing the larvae as they reach maturity.

Life Cycle and Description. The number of generations per year is reported to be two in Alberta and 2-3 in Washington. A complete life cycle is estimated to require 30-40 days. Overwintering occurs in the pupal stage.

  1. The eggs are deposited singly, usually on the underside of the foliage. They are pale yellow, hemispherical in shape, and marked with narrow vertical ridges. The eggs normally hatch in 3-5 days.
  2. Larvae have only three pairs of abdominal prolegs, and greatly resemble cabbage looper, Tricho-plusia ni (Hubner). The body is broader at the posterior end and narrower at the anterior end. As is the case with cabbage looper, the mature larva is predominantly green, but is usually marked with a distinct white stripe on each side. Dorsally, the larva bears several narrow, faint white stripes clustered into two broad white bands. When larvae hatch they measure less than 2 mm long, but at completion of the five

Alfalfa looper larva.

Alfalfa looper larva.

instars they attain a length of about 25-35 mm. Unlike the cabbage looper, the alfalfa looper tends to have dark thoracic legs, and a dark bar on the side of the head, or even an entirely black head capsule. Also, alfalfa looper lacks the small, nipple-like structures located ventrally on the third and fourth abdominal segments of cabbage looper. Alfalfa looper can be distinguished from bilobed looper, Megalographa biloba (Stephens), and celery looper, Anagrapha falcifera (Kirby) by the absence of numerous dark microspines on the body of alfalfa looper. A key to common vegetable-feeding loopers can be found in Appendix A. Duration of the larval stage is about 14 days. (See color figure 37.)

  1. The mature larva spins a loose, whitish silk cocoon, often incorporating leaves into the structure, and pupates within. The pupa is 18-20 mm long, and its color is blackish brown. Duration of the pupal stage is about 10-14 days.
  2. The moth measures 35-45 mm in wing-span. The front wings are gray with irregular light-brown and dark-brown patches. Near the center of each forewing there is a prominent silvery white or yellow-colored mark, which in general shape is said to resemble the hind leg of a dog. The hind wing is light brown or gray basally, and dark brown distally. The edge of both front and hind wings is marked with a series of dark spots. Unfortunately, the color pattern of the moths is not completely diagnostic, as there are other species with similar markings. LaFontaine and Poole (1991) should be consulted for keys to moths.

The biology of alfalfa looper is not well-cataloged. Hyslop (1912a) and Parker (1915) provided accounts of its ecology. Alfalfa looper is easily reared on bean-based artificial diet (Shorey and Hale, 1965). The larvae are included in the keys of Crumb (1956), Okumura (1962), and Capinera (1986). Adults are included in the keys of Eichlin and Cunningham (1978) and Capinera and Schaefer (1983). (See color figures 222 and 223.)

Damage

Larvae of alfalfa looper are defoliators. Initially, young larvae may be gregarious and skeletonize

Larva Spodoptera Linseed
Adult alfalfa looper.

leaves. They soon disperse, however, and chew irregular holes in foliage. They feed on the underside of leaves. A sign of their presence is large quantities of wet fecal matter adhering to foliage. When larvae are abundant they may disperse in large numbers from favored to less-favored plants. Alfalfa is often the source of such infestations.

Management

Alfalfa looper infrequently is a vegetable pest, though in the southwest it sometimes damages lettuce. Foliar application of Bacillus thuringiensis or chemical insecticides is effective. Careful monitoring is recommended, especially if late-season lettuce is grown in proximity to alfalfa or cotton. Lettuce is sensitive to injury, and an average of 0.25-0.5 larvae per plant likely warrants suppression. Components of the sex pheromone are known, and can be used to bait traps for population monitoring (Steck et al., 1979). Moths also can be captured in blacklight traps.

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