24 



FARMERS BULLETIN 804. 



SEASONAL HISTORY. 



The eggs are laid upon the cherry twigs in the fall and hatch 

 early in the spring. The insects are able to withstand freezing 

 weather, and after the return of warmer weather continue their 

 activities. Within two or three weeks after hatching the stem- 

 mothers are mature 

 and produce young. 

 These later gen- 

 erations become 

 adult usually in less 

 than a week. Some 

 of the insects so 

 produced become 

 winged while others 

 remain wingless. 

 The winged ones 

 migrate to some 

 plant not known, 

 and here the species 



I i y e s throughout 

 the summer. The 

 wingless ones con- 

 tinue reproduction, 

 and sometimes give 

 rise to as many as 



II generations be- 

 fore the end of 

 July. The num- 

 bers on cherry, 

 however, gradually 

 diminish, and dur- 

 ing midsummer 

 very few are seen 

 upon the trees, and 

 in some cases no in- 

 sects can be found 

 upon trees which 

 earlier in the sea- 

 son were badly infested. During October fall migrants and winged 

 males may be found returning to cherry trees and are often en- 

 countered during the migration period in larger numbers than might 

 be expected. The fall migrants produce the egg-laying females 

 which, when mature, are fertilized by the males. 



Fig. 17. — The black cherry aphis (Mijnis cerasi) : Curled 

 terminal cherry leaves following attack by this species. 

 (Original.) 



