PEA AND BEAN INSECTS 



73 



Fig. 49. — Winged viviparous female 

 of the pea aphis ( X 5). 



production continues for an average period of eighteen days 

 at the rate of one to eleven a day. The number of young 

 produced by a single female averages eighty. Both winged 

 and wingless forms are pro- 

 duced, the relative proportion 

 of the two varying with the 

 season and with the crowded 

 condition of the plant. The 

 wingless form (Fig. 50) re- 

 sembles the winged viviparous 

 female in color. The stems 

 become covered with the lice, 

 and the leaves, blossoms and 

 pods are soon attacked. In- 

 fested leaves become slightly 

 thickened and curled, infested blossoms are blasted and injured 

 pods are stunted, deformed and rendered worthless. Badly in- 

 fested plants take on a sickly yellowish appearance and may be 

 killed outright. Sometimes whole fields are destroyed in this 

 way. In such cases, the ground has a whitish 

 appearance from the cast skins of the plant 

 lice. Whenever the plants become crowded, 

 winged forms are produced that migrate to 

 other parts of the field or to other food plants. 

 In Virginia it has been found that while 

 breeding is more or less continuous throughout 

 the year on clover, the insect migrates more or 

 less regularly between its other food plants. 

 Fig. 50. — Wingless Peas are infested from April to the first of July 



viviparous female i »,, lii- -xxUi, 



pea aphis (X 5). wlien many or the plant-lice migrate to busn 



clover, sweet clover, alfalfa and the clovers. 



Peas again become infested in August and the plant-lice remain 



here until the advent of cold weather when they return to clover. 



Counting from the first-born of each brood, twenty or twenty- 



