320 Journal of Agricultural Research voi. xviii, no. 6 



FALL FORMS 

 PRODUCTION 



In this species only the apterous summer vivipara produced the fall 

 forms, no alate insects occurring in the experiments at a late enough 

 period for such production. 



One mother may produce fall migrants (alate sexupara) and males, 

 apterous vivipara and fall migrants, or apterous vivipara and males. 

 In two cases at least it seems very probable that one female produced 

 all three forms, but this cannot be stated with absolute certainty. 



Apterous vivipara and fall migrants were produced promiscuously, 

 just as were apterous and alate summer vivipara earlier in the season. 

 On the other hand, when males were produced they were the last progeny 

 of their mother, while the other form, whether it was the apterous vivi- 

 para form or fall migrant, constituted the earlier progeny. In this 

 manner, the males, while produced in the same generation with the 

 fall migrants, matured at about the same time as did the ovipara (prog- 

 eny of the fall migrants). In no case can it be certainly stated that 

 one mother produced only fall migrants; on the other hand, all of the 

 progeny raised from some of the apterous sisters of fall migrants were 

 males. 



FALL MIGRANT 

 MIGRATION 



As was the case with spring migrants, the actual migration of this 

 form did not occur as a swarming but was a scattered affair in the field, cov- 

 ering a period of from three to four weeks. This would be expected since 

 the fall migrants did not all occur in one generation but in several. 

 The insects may remain on the summer host for one or two days after 

 becoming adult; and they may spend an equal, or in a very few cases 

 even a longer period on the apple before reproduction begins. 



During the fall of 191 5 the apple-grain aphis was very abundant at 

 Vienna. After migration had been in progress for two or three weeks, 

 an examination of several old trees on the laboratory grounds revealed 

 the presence of migrants and their progeny on practically every leaf. 

 Almost no migrants were observed on the twigs, and those few were wan- 

 dering about. In the fall of 1914 these insects were not very abundant, 

 and only scattered migrants could be found on the trees. In so far as 

 could be determined no choice was shown in the selection of leaves. 

 Some insects were on leaves near the side branches and still others on 

 the watersprouts. Frequently, however, even in light infestations, the 

 insects would be found in groups of three or four on scattered leaves 

 rather than singly. 



