INJURIOUS TO CABBAGE AND CRUCIFEROUS CROPS 357 



common cultivated crucifers as well as many wild sorts, so that the 

 species is never without food. The small yellowish, oval eggs are 

 laid on end on the foliage, and are marked with prominent longi- 

 tudinal ridges. They hatch in from four to eight days. The larvae 

 grow very rapidly, gorging themselves on the foliage, which they 

 skeletonize in their well-known manner, and become full grown in 

 from ten days to two weeks. The mature cabbage worm is about 

 1 inches long, of a velvety green color, very similar to the foliage, 

 with a faint yellow stripe down the middle of the back and a row 

 of yellow spots one each side. The surface, when seen under a 

 lens, is finely roughened and dotted with small black specks. The 



FIG. 257. Pteromalus puparum, a chalcis-fly which parasitizes the cabbage 

 worm and many other injurious insects, male and female greatly enlarged- 

 hair line shows natural size. (After Chittenden, U. S. Dept. Agr.) 



chrysalis is attached to the foliage by a strand of silk around the 

 thorax and is first greenish and later light brown in color. The 

 butterflies emerge in from 'one to two weeks in the summer, but 

 the chrysalides of the last generation in fall hibernate over winter 

 among the old stalks and rubbish on the fields. Thus the whole 

 life cycle in summer requires from three to five weeks. In New 

 England there are three generations a season and there are prob- 

 ably five or six in the extreme south, as the butterflies there remain 

 on the wing all winter. 



Enemies. Fortunately, the parasites of the cabbage worm are 

 .becoming very effective in checking its multiplication, and in 

 many sections of New England where it has existed the longest, 

 it rarely becomes very injurious, so well do the parasites control 



