324 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



aphides develop as often as the food-plant becomes overcrowded 

 and it is necessary to migrate to avoid starvation. 



By midsummer, with the harvesting of the peas, most of the 

 aphides upon them have been destroyed by predaceous and para- 

 sitic insects and disease, and they are not observed during late sum- 

 mer unless they have been subsisting on clover throughout the 

 season, when they sometimes destroy the crop in August, as has 



FIG. 234. The pea-aphis on stems of red clover natural size. 



Folsom.) 



(After 



been observed in Illinois. In early fall they often become com- 

 mon again on late garden peas, and late in October they migrate 

 to clover. Fewer young are born as the weather gets colder in 

 the fall, and the aphides never become numerous enough to do any 

 injury at that season. Late in October and early November in 

 the Middle States as the aphides are migrating to clover, winged 

 males appear, and some of the wingless females developing on 

 clover produce eggs. The winged males are similar in size and color 



