The Imported Cabbage Worm (Pontia Rapae) is generally recognized to be the most important insect enemy of cabbage and several closely related crops. The pest was first seen in North America in i860 at Quebec, five years later in Maine. Now it is distributed throughout the United States. The butterfly is familiar to all garden makers. It is white, with a wing expanse of nearly 2 inches. There are two conspicuous black spots on each fore-wing of the female and only one on the fore-wings of the male. The full grown larva is over an inch long. It is nearly green and finely dotted with small black spots. A faint yellow stripe marks the middle of the back with a row of yellow spots on each side in line with the spiracles. The pale yellowish eggs are deposited singly, and usually on the underside of the leaves.
The butterflies appear early in spring, and in a few days begin laying eggs, which hatch in four to eight days, the larvae attaining full maturity in from ten days to two weeks. The chrysalis stage during the summer months lasts from one to two weeks. The insect also passes the winter in the chrysalis form. There are three broods in the North in one season.
Several natural enemies of this pest assist the grower in controlling it, but it is often necessary to use insecticides. All points considered, arsenate of lead is probably the most effective poison in destroying cabbage worms. Other remedies are hot water, kerosene emulsion, and pyrethrum.