Crucifer Pests
 

Imported Cabbage Worm
Pieris rapae

Found worldwide, especially in cooler areas

Damage Symptoms

The damage of imported cabbage worm (ICW) is similar to that caused by the cabbage looper. Caterpillars may bore directly into the heads. The first leaves of cabbage have large irregular-shaped holes. Between the leaves, you can find pelleted frass that has a very strong smell. This may influence marketability.

Insect Characteristics

Chewing mouthparts. The caterpillars are velvety green in color, are quite hairy and have a thick orange stripe down the middle of their backs. They blend with the leaf foliage. Adult butterflies are easily recognized. They are white, yellow or orange with black spots on their wings. They flutter about during the day.


Where to Look

Look at the first-formed leaves of the heads for ragged, irregular-shaped feeding holes. The insects bore into the heads. By peeling back the leaves, you will be able to detect pelleted frass and other remains. The pungent smell should be evident.


Technical information

Females lay eggs singly on the undersides of the leaves. Caterpillars are voracious eaters and reach full growth in about 14 days. They move very slowly. Pupation occurs on the plant in the form of a hanging chrysalis (pupa).

Control

Most formulations of Bacillus thuringiensis are effective against ICW. Several chemicals are effective and there are no reports of ICW developing resistance to any insecticides.

Parasites and pathogens play a significant role in the natural control of ICW. Apanteles glomeratus is a common larval parasite that occurs practically worldwide. Phryex vulgaris and Pteromalus puparum are other species of hymenopterous parasitoids that attack ICW. A granulosis virus specific to ICW attacks larvae; this virus is commonly found in Taiwan.