APHIDS INJURIOUS TO ORCHARD FRUITS. 



13 



appear. The true sexes, therefore, appear from the tenth to the 

 nineteenth generation, depending upon the rate of reproduction of 

 their ancestors and upon the time of 

 their birth — that is to say, whether thej^ 

 are early or late young of the parents. 

 The egg-laying females become adult 

 in from 6 to 16 days, depending upon 

 weather conditions. When adult the}" 

 mate with the males and begin deposit- 

 ing their eggs upon the apple twigs. 

 Females may be found on the trees until 

 all the leaves have fallen, even when the 

 weather is very cold. 



THE OAT APHIS.i 



The oat aphis, sometimes called the 

 European grain aphis, is the earliest 

 apple aphid to hatch in the spring ; and as 

 it often occurs in great abundance upon 

 the buds and young foliage, it is fre- 

 quently the cause of alarm on the part 

 of orchardists. The species probably 

 does not cause important injury, since 

 it migrates from the apple shortly after 

 the blossoms fall. 



When first hatched the stem-mothers 

 are very dark green, and they remain 

 this color until after the first molt, when 

 the}" become much paler. The adult 

 wingless forms are pale green, with 

 rusty areas around the base of the honey 

 tubes, although in the summer some in- 

 dividuals become slightly purplish. The 

 winged forms have black head and body 

 with a green abdomen which is marked 

 with black patches along the sides. The 

 honey tubes, antennae, and feet are black. 

 The egg-laying females, which occur in 

 the fall, have an olive cast. 



SEASONAL HISTORY. 



During warm days in winter many 

 of the eggs of this species hatch on the 



Fig. S. — The green apple aphis : 

 Winter eggs on apple twig. 

 Much enlarged. (Original.) 



Aphis avenoc Fab. 



