8 Circular 107 



The cabbage aphis passes the winter as an egg upon rape, turnip, 

 brussels sprouts, kohl-rabi and cabbage. Hatching occurs in late 

 March and early April and generation of females follows generation 

 until mid-fall when true males and females appear and the over- 

 wintering eggs are laid. 



All summer broods produce a proportion of winged lice and the 

 flight which occurs serves to distribute the lice throughout the plants 

 of the cabbage family. 



Beginning in spring the lice increase steadily in number until 

 warm weather comes on. Then natural parasitic enemies develop 

 even more rapidly and destroy vast numbers. When the cool weath- 

 er of fall arrives the lice again increase in numbers until the cold 

 weather stops further breeding. 



The False Cabbage Aphis 



(Aphis pseudobrassicae Davis) 



Fig. 5 



The False Cabbage Aphis 



1 — Adult winged female ; 2 — Immature female ; 3 — Adult wing- 

 less female 



This, like the cabbage aphis, is covered with a powdery coating, 

 but the coating is neither so heavy nor so complete as in the case of 

 the true cabbage aphis. 



It attacks a variety of plants within the cabbage family, being 

 found on turnips, radishes, cabbage, kale, wild mustard, black mus- 

 tard, rape, wild radish, 10 weeks stock and shepherd's purse. 



