INSECTS INJURIOUS TO CABBAGE AND OTHER CROPS I37 



careful cook and housewife. It begins work early in the season, 

 when the principal damage is usually accomplished, and after 

 riddling the outer leaves, attacks the more tender inner leaves 

 as they form, frequently secreting itself in the heads, which 

 are made most unsightly by its excrement. This species was 

 first observed in the United States in 1865 and in about a score 

 of years it had invaded nearly every state and territory in our 

 domains. 



All cruciferous crops, but particularly cabbage and cauli- 

 flower, are attacked, as are also nasturtium, mignonette and 

 some allied plants. The butterflies are on the wing from early 

 morn till dusk. As early as March they can be seen flying about 

 cabbage fields and they continue until after severe frosts. The 

 observed egg period is from 4 to 8 days. The larva eats 

 voraciously and grows with rapidity, attaining full growth in 

 from 10 to 14 days after hatching. The summer-time chrysalis 

 period is from 7 to 14 days, but the last chrysalides remain 

 undeveloped until the following spring. The life cycle has 

 been traced from between 22 days to five weeks. Even in New 

 England this species is credited with being triple brooded, but 

 in the District of Columbia and vicinity there must be one or 

 more additional generations, and there is a possibility of still 

 more in the extreme South. 



A natural enemy of this species, Pteromahts piiparum, is 

 shown in figure 89, and. a "worm" parasitized by Apantcles 

 glomeratus is illustrated by figure 90. 



In treating this species it should be borne in mind that other 

 "worms" and pests are more often present than otherwise. 



Arsenicals. — The best remedy is Paris green applied, prefer- 

 ably as a spray, at the rate of about one pound of poison to 

 150 gallons or less of water, and it should be used when plants 

 are first set out, to insure its reaching the young "worms" be- 



