INJURIOUS TO CABBAGE AND CRUCIFEROUS CROPS 373 



sprouts and kohl-rabi, but are most abundant on cabbage, particu- 

 larly in the crevices and depressions of the under surfaces of the 

 leaves. On leaves taken at random from a badly infested patch, 

 from 177 to 293 eggs were found on a leaf. Two to three eggs are 

 laid by each oviparous female. When first laid the eggs are a 

 yellowish-green, but soon turn a shining black. From eggs taken 

 at random and left under normal outdoor conditions, 76 per cent 

 hatched the next spring, while all eggs hatched which were laid by 

 females known to have been fertilized. Eggs hatched about 

 April 1, 1910, in central New York, the season being an early one. 

 From the stem mothers which hatched from these eggs, twenty- 

 one generations of wingless females were reared up to December 3, 

 1910, the average length of a generation being about twelve days. 

 During the summer generations of winged females are produced, 

 especially on crowded plants, and these serve to spread the pest to 

 unaffected plants. The wingless females become full grown in 

 about thirteen days during the summer and live for about forty-six 

 days, during which time they will give birth to an average of forty- 

 one young, producing as high as six young in a day. The winged 

 forms are much shorter lived, living only about ten days and giving 

 birth to but from seven to thirteen young. 



There is no question that in the Southern States the viviparous 

 females may continue to reproduce all winter, and it is quite prob- 

 able that some of them survive in pits and cellars in the North, 

 where eggs also probably occur. Thus Sirrine* states that it " is 

 certain that this aphid can survive the winter on cabbage stored 

 in cellars or pits, also that cabbage stored in pits for seed purposes 

 furnishes the supply of aphides for infesting the seed stalks in early 

 spring." This being the case it should be an easy matter to 

 destroy the aphides by fumigation before removing them from 

 the pits. 



Control. From the habits outlined it is evident that, as for 



other cabbage pests, the refuse of the crop should be cleared up and 



destroyed in the fall. Any of the standard contact insecticides, 



such as kerosene emulsion, 1 part stock solution to 15 parts of 



* F. A. Sirrine, Bulletin 83, N. Y. Agr. Exp. Sta., p. 675. 



