Melanchra picta Harris Lepidoptera Noctuidae

Natural History

Distribution. This native insect is found in southern Canada and the northern United States from the Atlantic to the Pacific Coast. Nowhere is it considered to be a major pest, yet it can be a fairly regular nuisance, and a significant component of the defoliator pest complex of several crops.

Host Plants. Zebra caterpillar feeds on several vegetable plants, and has been recorded as a pest of asparagus, bean, beet, broccoli, cabbage, celery, corn, lettuce, parsnip, pea, potato, rutabaga, spinach, tomato, and turnip; cabbage seems preferred. It also attacks flowers such as aster, hydrangea, and sweetpea, field crops such as alfalfa, clover, rape, sugarbeet, and tobacco, and trees such as apple, plum, and willow. As might be expected from an insect with such a broad host range, zebra caterpillar feeds on many weeds. Much of the economic entomology literature reports this insect as a pest of sugarbeet.

Natural Enemies. A nuclear polyhedrosis virus (NPV) of zebra caterpillar causes marked decreases in abundance, especially when larval densities are high (Adams et al., 1968). Signs and symptoms of infection include loss of appetite, sluggish behavior, and reduced larval growth rate. Mortality occurs within 14 days of ingesting the polyhedral inclusion bodies, and dead larvae can be found hanging from foliage, suspended by their hind prolegs. Soon after death, larval color darkens, and the cadavers turn black and rupture. Body contents, including virus polyhedra, contaminate the foliage, enhancing spread of the disease. There is some evidence that other armyworms and cutworms may be infected by M. picta NPV.

Parasitoids known to attack zebra caterpillar include Limneria annulipes Harris (Hymenoptera: Ich-neumonidae), Microplites mamestrae Weed (Hymenop-tera: Braconidae), and Winthemia quadripustulata (Fabricius) (Diptera: Tachinidae) (Li et al., 1993).

Life Cycle and Description. There are two generations per year over most of the range of this insect, generally occurring in June-July and August-October. A complete life cycle requires about 60 days during the summer. Zebra caterpillar overwinters in the pupal stage.

  1. The moths are highly fecund, often depositing 1200 white, ovoid, slightly flattened eggs in clusters of 100-200, usually on the underside of leaves. As might be expected from an insect with a northern distribution, eggs do not hatch at high temperature, 32° C and higher. Excellent survival occurs at about 27°C, and hatching time is about five days. At 21 °C, excellent hatching also occurs, but development is delayed to about six days. Hatching is inhibited at 15° C, and development time extended to about 12 days. At 10°C, eggs fail to develop.
  2. The mature larva is boldly colored black, yellow, and white, and is immediately recognizable. The sides are yellow and white, with a vertical row of short-black stripes running the length of the body. There is a black band dorsally, separating the yellow and zebra-stripe lateral bands. The underside of the caterpillar is orange or red. Young larvae are very difficult to identify; they are principally black and green. However, they feed gregariously until they are about one-half grown, and this behavior helps to distinguish them. There are six instars. Head capsule widths are about 0.3, 0.5, 0.9, 1.5, 2.1, and 3.0 mm for the six instars, respectively. The average larval length is about 3.5, 6, 10, 17, 27, and 37mm, respectively. Development time averages 3.5, 2.9, 3.3, 3.0, 3.4, and 7.2 days for larvae reared at 27°C. The last 3-4 days of the terminal instar is usually spent in the soil, where the larva prepares to transform into a pupa. (See color figure 66.)
  3. The pupa is dark brown, and measures about 2 cm long. The males weigh about 400 mg and the females are slightly heavier, about 450 mg. Pupal development time is about 30 days. This is the normal overwintering stage.
  4. The adult wingspan measures about 3.54.5 cm. The front wings are chocolate brown, with a weak gray spot centrally. The hind wind is white, but bears a narrow brown band at the wing margin. Moths begin to emerge as early as 45 days after eggs are deposited, but usually about two months is required for a complete generation to occur. The pre-ovi-position period of moths is about two days. Moths may continue to deposit eggs for a period of up to two weeks, although most oviposition occurs within one week. Adults perish after 10-12 days. (See color figure 253.)

Zebra caterpillar larva.

Zebra caterpillar larva.

Zebra caterpillar pupa.

Zebra caterpillar pupa.

Adult zebra caterpillar.

The biology of zebra caterpillar was given by Tamaki et al. (1972) and Capinera (1979a).

Damage

The larvae are leaf-feeders, and initially they feed gregariously. They may make small holes or skeletonize foliage early in their development, but they soon become voracious, eating large holes in foliage. Larvae often completely consume individual leaves, leaving only the stem or petiole before moving to new food. Foliage consumption and damage potential on sugar-beet were given by Capinera (1979).

Management

These insects are not difficult to kill with foliar applications of chemical insecticides or Bacillus thurin-giensis. They also are susceptible to the botanical insecticide neem, which functions as a feeding deterrent and growth regulator (Isman, 1993). Because of their seasonal biology, they sometimes develop to damaging levels late in the season, after the threat of insect damage is generally past. Thus, continued vigilance is suggested if the insects have been observed earlier in the season. Zebra caterpillar is susceptible to infection by Autographa californica NPV (Capinera and Kanost, 1979).

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Responses

  • mandy eisenberg
    How many eggs do melanchra picta lay?
    5 years ago

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