IMPORTED CABBAGE WORM 229 



inch. The female lays her eggs in leaves or stems, and the larvae 

 feed within the tissues, also boring into the tuber, where the most 

 serious harm is caused. It is to be noted that this injury occurs 

 both in the field, while the tubers are yet in the ground, and while 

 they are in storage (Figs. 237 and 238). 



Injury. The quality and consequently the salability of the 

 potato crop in some sections is at times seriously affected by this 

 evidently introduced pest, particularly if the potato market in the 

 early fall is slow, necessitating the holding of the tubers by growers. 

 The insect occurs in California in abundance, in Washington, 

 Texas and other southern and western states, and appears to be 

 spreading northward. It is an enemy, but not a serious one, of 

 tobacco also. (See tobacco insects.) 



Control. Hogs turned into an infested field after removal of 

 the crop will consume practically all tubers left therein, with the 

 contained larvse. Infected potato plants, as well as weeds and all 

 volunteer plants, should be burned. As in the case of many other 

 insects, crop rotation is advised. Avoid having potatoes, tobacco, 

 tomatoes, or egg-plants follow each other, since they are all host 

 plants of this insect. 



Stored potatoes, if infected, should be fumigated with hydro- 

 cyanic acid gas or bisulfid of carbon, using the latter at the rate 

 of three pounds for every one thousand cubic feet of air space, 

 and exposing to fumes in an air-tight house, or in bins, or in air- 

 tight barrels for twenty to twenty-four hours. Use precautions 

 against fire. This fumigation should be repeated two weeks later. 



In fumigating with hydrocyanic acid gas the cubical content 

 of building, room, or receptacle must be determined and the dosage 

 based upon that. (See page 61.) An expert should be consulted. 



CABBAGE INSECTS 



The Imported Cabbage Worm. The adult of this insect (Pontia 

 rapce Sch.) is the familiar white cabbage butterfly. The female 

 has two black spots on each fore-wing the male but one (Fig. 

 239, a and 6). Both sexes have a black spot on the anterior mar- 

 gins of the hind-wings. The caterpillars are velvety green, about 

 one or one and one-half inches long. They have a faint yellow 

 stripe down the center of the back and a row of yellow spots on 

 both sides. 



Life History. The butterflies are seen early in the spring and 

 summer, flying over the fields and depositing their yellowish eggs 



