INSECTS INJURIOUS TO CABBAGE AND OTHER CROPS I39 



cabbage stalks in the field after the crop has been secured is 

 reprehensible. Remnants should be destroyed, with the exception 

 of a few left at intervals through a field as traps for the females 

 for the deposition of their eggs. These plants should be freely 

 poisoned with arsenicals, so that the last generation will not 

 develop. 



The Southern Cabbage Butterfly (Pontia protodice Boisd.).— 

 Before the advent of the imported cabbage butterfly, the present 

 species was the occasion of considerable injury, particularly 



llhuiJ 



Fig. 91.— Southern cabbage butterfly 

 worm. (After Riley) 



Fig. 92.— Potherb butterfly. Adult above, 

 larva below. (After Harris) 



southward. Of late it has disappeared in many regions, but 

 occasionally makes its reappearance for a limited period. In 

 many respects it resembles the preceding, and the male as it is 

 seen flitting lazily through cabbage fields and gardens would 

 n£ver be recognized as distinct from the more injurious form. 

 The "worm" (fig. 91) varies from pale to dark blue or green, 

 is striped with yellow and covered with black spots bearing 

 black hairs. 



Remedies. — The treatment is the same as for the preceding. 



The Potherb Butterfly (Pontia napi Linn.). — This butter- 

 fly is found in the more northern and eastern portions of 

 North America, and is distinguished from others attacking cole 

 crops by its nearly uniform white wings without spots. The 

 larva (fig. 92) is uniform pale green, and resembles the cab- 



