Imported Cabbageworm

Imported Cabbageworm Pieris rapae (L.)

Kimberly Stoner
Department of Entomology
Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106

Telephone: (203) 974-8480 Fax: (203) 974-8502
E-mail: Kimberly.Stoner@ct.gov
When and Where to Look

The adult butterflies are out feeding at flowers and laying eggs from very early in the spring -- as early as the first warm sunny days in April. The eggs, larvae, and pupae are found on plants in the cabbage family, including broccoli, cauliflower, collards, kale, Chinese cabbage, and Brussels sprouts, as well as cabbage. The larvae also feed occasionally on turnips, radish, mustard, and even lettuce. There are many overlapping generations per year. When large larvae are feeding, you will find wet masses of dark green excrement dropped on the surfaces of leaves below. The imported cabbageworm overwinters as a pupa, attached to any convenient stem, branch, fencepost, or other hard surface in the area.

Description

• Adult: The adult is a very commonly seen white butterfly with black-tipped front wings with one or two black dots and one black dot on the hind wings.
• Egg: Each pale yellow, bullet-shaped egg is laid singly on the leaf, usually on the underside.
• Larva: The velvety green caterpillar has a faint yellow stripe down its back and a row of faint yellow spots on each side. When fully grown, it is slightly more than 1 inch long.
• Pupa: The pupa or chrysalis is green or tan, 3/4 of an inch long, and attached to the plant or other surface by silken threads.
• Damage: The larvae eat large holes in the leaves. As they feed, they frequently move toward the center of the plant, so they feed directly on cabbage heads and on leaves shading cauliflowers from the sun, dropping their wet masses of excrement all over the cabbage or cauliflower head. They are also often found inside broccoli heads when they are cooked.

Control Methods

Natural: Red cabbages, savoy cabbage, and glossy collards are less susceptible to imported cabbageworm. Several plant breeding programs are working on developing glossy varieties of cauliflower, broccoli, and other crops that will be resistant. Bacillus thuringiensis (trade names: Dipel, Thuricide, Bt, etc.) is a bacterium which effectively kills imported cabbageworm larvae, but it is most effective when the larvae are still small.

Barriers like row covers or a nylon stocking stretched over a cabbage head can keep the butterflies and thus caterpillars out.

The imported cabbageworm has many insect natural enemies, including several parasitic wasps, and predators of eggs and young larvae. You may find dead caterpillars with a large mass of white or yellow cocoons nearby. The cocoons are from a parasitic wasp introduced to this country as an enemy of imported cabbageworm.

Chemical: In addition to the bacterial insecticides, Sevin, methoxychlor, rotenone, and pyrethrum are available in formulations labeled for control of imported cabbageworms. Follow instructions on the label.

Summary

The imported cabbageworm adult is one of the most common butterflies in Connecticut. The caterpillar of this butterfly is the velvety green "worm" that feeds on leaves of plants in the cabbage family. These caterpillars can be controlled with microbial insecticides based on strains of Bacillus thuringiensis effective against caterpillars, or row covers can be used to keep the adults from laying eggs on plants in the garden.