IMPORTED 
 CABBAGE WORM 
 
 a 
 
 d, a, a, Butterflies (or adults) with wings in natural positions; 
 b, b, larvae (caterpillars, or "worms"); c, c, pupae (chrysalids — 
 the resting stage); d, cabbage plant showing typical feeding injuries. 
 (Upper illustration: a, b, and c about one-halt natural size: d 
 slightly less than two-thirds natural size. Lower illustrations: a, 
 b, and c about natural size. 
 
 • r life history and control] 
 
 : - 
 
 Department af Agr 
 
 Picture Sheet N 
 
IMPORTED CABBAGE WORM 
 
 (Picris rapac (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 m 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 i^r 
 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 10 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 
 2.") pounds per acre per application. 
 
 Fresh pyrethrum 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 belter 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){ pounds of a derris powder (containing 4 percent of rotenone) to ."><) 
 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. 
 
 April l!»il r. S. Government Printing Office 
 
 For sale by the Superintendent of Documents, ||l|Hl!K^^ 111 1 1 
 
 3 1262 09082 4672