10 Farmers’ Bulletin 1128. 
some develop into winged forms, or migrants (Pl. II, H), and some 
remain wingless (Pl. II, E, G, I. They mature in a little over a 
week, and in turn produce either winged or wingless forms. Occa- 
sionally another form, intermediate between the winged and the 
wingless forms, is seen. This reproduction continues throughout 
the summer, from 9 to 17 summer generations occurring before the 
sexual forms 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 they are early or late young of the parents. 
The egg-laying females become adult in from 6 to 16 days, depend- 
ing upon weather conditions. When adult they mate with the 
males and begin depositing 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 APPLE-GRAIN APHIS.' 
The apple-grain aphis, or the apple-bud aphis, has been confused 
in this country with the oat aphis * or European grain aphis, an in- 
sect which is not common here but which occurs in Europe on the 
bird cherries. Both insects spend the summer on grains and grasses 
and on these plants look very much alike, but the apple-grain aphis 
lives during the winter months on apple and not on cherry. It 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 frequently 
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. (Pl. IV, A,-B, C, D.) 
When first hatched the stem-mothers are very dark green, and they 
remain this color until after the first molt, when they become much 
paler. The adult wingless forms are pale green (Pl. IV, E), with 
rusty areas around the base of the honey tubes, although in the sum- 
mer some individuals become slightly purplish. The winged forms 
have black head and body with a green abdomen which is marked 
with black patches along the sides. (Pl. IV, F.) The honey tubes, 
antenne, and feet are black. The egg-laying females, which occur 
in the fall, have an olive cast. (PI. IV, N.) 
SEASONAL HISTORY. 
During warm days in winter many of the eggs of this species hatch 
on the trees, but it is not until about the middle of March, in the 
vicinity of Washington, that those hatching succeed in escaping de- 
struction and produce stem-mothers. In fact, aphids from eggs 
hatched before April 1 are sometimes all killed by cold. The im- 
portant hatching, therefore, commences after April 1. 
1 Rhopalosiphum prunifoliae (Fitch). 2 Rhopalosiphum padi (L.) (avenae Fab.). 
