VEGETABLE INSECTS 



185 



the following spring. We found them hatching on the 

 thirty-first day of March. We found that there were thirty 

 generations during the year and that there was an aA^erage 

 of about twelve days for each generation. That accounts 

 for the enormous numbers of lice that appear in the field 

 during the fourth or fi.fth generation, the latter part of June, 

 July, or August. The eggs are black or very dark brown, 

 and they look like tiny footballs. 



I want to bring out the point that the eggs rest on the 

 leaves all winter long. The old cabbage stumps in the spring 

 will throw out tender, succulent shoots, and it is there that 

 the aphis in the spring of the year finds food ready for its 

 liking. On the thirty-first day of March Ave found the aphids 

 feeding on one of these sprouts. One of the things Ave must 

 do to control the cabbage aphis is to clean up old stumps and 

 leaves. 



Question : If they are ploAved under, Avill the aphids live 

 over ? 



Professor Herrick: I am afraid you cannot ploAv long 

 cabbage stems under. We have tried that here in an experi- 

 mental field. We did as good a job of pIoAving as almost any- 

 one could do, and yet AA'here no pains Avere taken to pull up 

 the stumps and lay them flat in the roAv, they still projected 

 aboA'e the soil. 



Question : With a disc harroAv they can be cut up before 

 ploAving, can they not? 



Professor Herrick: Possibly. We did not try it. 



A Member: We sometimes cut them off Avith spades and 

 send them to market. It is not a very long job to chop them 

 off AAuth a sharp spade. 



Professor Herrick: I Avant to say a Avord regarding 

 spraying for the cabbage aphis. During the summer of 1911 

 I sprayed a badly infested field of cabbage containing two 

 acres to see AA'hat Ave could do to control the aphis, and to 

 see AAdiat material AA'ould kill it best, and to see AA^hether it 

 could be done economically. In spraying that field of tAA^a 

 acres, Ave used a knapsack sprayer. We sprayed them Avith_ 



