IMPORTED CABBAGE WORM 
(Pieris rapae (L.)) 
General Life History 
The imported cabbage worm is the larva of a white butterfly, 
which passes the winter in the chrysalis or pupal stage in the Northern 
States. In the more southerly States the larvae, or “worms,” may be 
found from March until December, and in some areas throughout the 
winter. The butterflies emerge from the chrysalids early in the spring. 
The female butterfly deposits each egg separately, in contrast to the 
habit of many other insects which deposit their eggs in masses. The 
eggs are usually laid on the under side of the leaves of cabbage, collards, 
cauliflower, broccoli, and other food plants. The time required for 
the various stages of the insect to develop varies with the season. 
However, the eggs usually hatch within a week, and the larval and 
pupal stages each develop in from 1 to 2 weeks; so there are several 
broods each year, ranging from 3 to 6 in different parts of the country. 
The velvety-green larvae, or caterpillars, are especially fond of the 
tender, immature heads of cabbage, to which they often cause severe 
injury. 
Control 
The imported cabbage worm is readily controlled by the use of 
one of several insecticides. 
The safest and one of the most effective methods is the use of a 
derris or cube dust mixture containing from 0.75 to 1.0 percent of 
rotenone. Applications should be made at intervals of about 10 days 
from the time the caterpillars are first discerned on the plants until 
such time as the pest is brought under control or the harvesting of the 
crop is completed. The dust may be obtained already prepared, in 
which case the amount of rotenone present is shown on the package; or 
it may be made by mixing the derris or cube root powder with talc, 
pulverized clay, sulfur, or tobacco dust. For example, to prepare a 
%-percent rotenone dust from a derris powder which contains 4 percent 
of rotenone, use 1 pound of derris to 5 pounds of the talc or other 
material; for larger quantities, use 16 pounds of the derris to 84 pounds 
of other material. For best results the dust applications should be 
made late in the afternoon or early in the evening when the air is 
practically calm and the plants are slightly moist with dew. Special 
care should be given to see that the insects and the “buds,” or heads 
of the plants, are reached by the insecticide. The dosage will vary 
according to the size of the plants, but should range from about 10 to 
25 pounds per acre per application. 
Fresh pyre thrum flowers powder (containing approximately 0.9 
percent of total pyrethrins) diluted with 2 parts of talc or one of the 
other materials listed will also give satisfactory control. 
Although dusts have, in general, given better results than sprays 
in controlling the imported cabbage worm, the materials previously 
mentioned may be applied as sprays. A spray consisting of from 2 to 
2 y 2 pounds of a derris powder (containing 4 percent of rotenone) to 50 
gallons of water, to which may be added a nonalkaline spreader or 
sticker, is recommended. Sprays made from extracts of derris or 
pyrethrum, or a combination of them, when prepared according to the 
manufacturer’s directions, may also be used. 
16—20765 
April 1941 
U. S. Government Printing Office 
For sale by the Superintendent of Documents, Washington, D. C.- — Price 5 cents 
