INJURIOUS TO CABBAGE AND RELATED CROPS 23 



Fig. 19. — Egg of 

 the cabbage aphis 

 (X 19). 



plants. In some seasons the losses are severe, the crops over 



large areas being so badly infested that the growers plow them 



under early in the season. 



In that part of its range in which the winters are severe, 



the cabbage aphis hibernates exclusively in the egg stage; 



farther south many of the lice doubtless _ 



survive the winter. The elongate, oval, 



smooth, black, shiny eggs (Fig. 19), about 



3^8- inch in length, are found abundantly on 



the petioles and under surface of the leaves 



of cabbage plants left in the field over 



winter. Early in the spring the eggs hatch 



and the young lice find abundant food in 



the tender sprouts thrown out by the old 



cabbage stumps (Fig. 20). These lice of the 



first generation hatching from the eggs are all wingless females 



and are known as stem-mothers. As they increase in size, the 



lice molt four times, reaching 

 maturity in about two weeks. 

 A few days after the last molt 

 they begin to give birth to living 

 young. These stem-mothers 

 may live for six weeks or more 

 and give birth to forty or fifty 

 young. The next generation of 

 lice consists of wingless agamic 

 females which resemble the 

 stem-mothers very closely in 

 form and color, being about 

 Yo" inch in length, grayish green 

 in color and covered with a 

 whitish waxy bloom (Fig. 21). 

 During the remainder of the 

 season reproduction continues 



/ 



'■i/r' 



Fig. 20. — Stem-mothery of tlie 

 cabbage aphis feeding on a 

 sprout thrown out Ijy an okl 

 cabbage stump (greatly en- 

 larged) . 



