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