Purplebacked Cabbageworm Evergestis pallidata Hufnagel Lepidoptera Pyralidae

Natural History

Distribution. This is a decidedly northern species, and is found throughout most of Canada except for British Columbia, and as far south as Virginia and Kentucky in the eastern United States, and northern Arizona in the West. It is likely of European origin, but has been in North America at least since 1869. It is recorded as a pest principally in Canada's Maritime Provinces.

Host Plants. Purplebacked cabbageworm feeds on a variety of cruciferous plants, including broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, horseradish, kale, kohlrabi, radish, rutabaga, and turnip. Horseradish and turnip seem to be most favored by this insect. Although moths deposit eggs on shepherdspurse, Capsella bursa-pastoris; and sheep sorrel, Rumex acetosella; larvae do not develop successfully on these plants.

Natural Enemies. Few natural enemies are known. The wasps Bracon montrealis Morrison and Meteorus autographae Muesebeck (both Hymenoptera: Braconidae) have been reared from this caterpillar.

Life Cycle and Description. There is only a single generation annually in Newfoundland, but two generations per year in Virginia. Overwintering occurs as a mature larva (prepupa) in the cocoon.

  1. The female deposits small batches of about 3-12 eggs on the underside of host plant foliage. The bright yellow, oval eggs are about 1.1 mm long and 0.8 mm wide, flattened, and overlap like fish scales. The eggs darken markedly just before hatching. Larvae hatch in 4-8 days.
  2. Newly hatched larvae are whitish green, and measure 1.5-2.0 mm long. The body bears numerous dark tubercles, each bearing one or more hairs. Head capsule widths are about 0.3, 0.5, 0.9, and 1.6 mm for the four instars, respectively. Duration of the instars is reported to be about 9.1, 8.9, 10.3, and 25.7 days, followed by a protracted prepupal period. Larvae are nocturnal, and are usually found hiding between leaves during the day. Mature larvae are robust, bristly, and darker in color, normally olive-green to purple-brown, and measure about 20-22 mm long. There is a conspicuous yellow band on each side, with a narrow white band beneath, and the larva is colored ash-gray or greenish below. The body tapers at both the anterior and posterior ends. The larvae feed on the underside of leaves, then drop to the soil to prepare a cocoon.
  3. The cocoon is oval, about 12-15 mm long, and covered with soil particles. The winter is passed as a prepupa in the cocoon, with pupation occurring in the spring. The pupa is light to dark brown.
  4. The moth escapes through a loosely constructed end of the cocoon. The moth has a wingspan of about 22-28 mm. The front wings are straw yellow, with irregular, narrow dark lines crossing the wing. The hind wings are whitish or pale yellow with darker margins.

Morris (1958), Munroe (1973), and Howard et al. (1994) provided the biology of purplebacked cutworm.

Damage

Larvae generally eat holes in the leaves, webbing them together, but also attack the crown and even the roots of such crops as rutabaga. Morris (1958) reported that it was a serious pest in Newfoundland, but its abundance varied widely from year to year.

Management

Moths can be attracted to traps baited with pheny-lacetaldehyde, which offers the potential for population monitoring (Cantelo et al., 1982). Chemical insecticides and Bacillus thuringiensis can be applied against the larvae, but this is usually a minor pest as compared to other crucifer-feeding caterpillars. Spring tillage can destroy the cocoon, and deep tillage can prevent the moths from emerging. Early planted turnip can be used as a trap crop to help protect cabbage and rutabaga.

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