31 6 Journal of Agricultural Research voi. xviii, no. 6 



SUMMER FORMS 



The great majority of the insects living upon oats during the summer 

 are apterous. During the early part of the season, however, a considerable 

 number of alate insects were reared. These occurred in all generations 

 from the second to the twelfth of the summer forms and the fourth 

 to the sixteenth ^ from the egg. It should be noted, however, that the 

 general distribution of the summer alate form was limited to the first 

 seven summer generations. Such forms were limited to four lines after 

 that period, and in three of these four lines the form occurred only once. 

 In the other line alate individuals, or at least forms other than apterous, 

 occurred in five consecutive generations after the appearance of such forms 

 had ceased in practically all other lines. In all cases these were the 

 progeny of apterous mothers, no attempt being made to rear young 

 from the alate insects. This might seem to indicate that the alate form 

 was an inheritable character, for this particular line at least. The appear- 

 ance of this insect in this series of experiments can hardly be traced to 

 food conditions, since the food was changed two or three times in the 

 course of the five generations. Strong negative proof is also furnished 

 by the fact that in other lines the food was so poor at times that we had 

 difficulty in maintaining the insects, yet no unusual number of alate 

 aphids appeared and, in fact, in many cases no winged forms at all devel- 

 oped. It should be added that the percentage of the alate insects 

 occurring in the five generations under discussion was small. 



In addition to the two common forms, intermediates occurred in five 

 experiments. In four experiments they were accompanied by both 

 apterous and alate forms, as was found by the authors to be the case 

 in Aphis pomi? In the fifth experiment no alate forms were ob- 

 tained. Several pupae were lost in this case, however; and since only 

 2 or 3 intermediates developed from lo or 12 pupae in the other experi- 

 ments, it appears quite probable that some of these lost pupae would 

 have developed into alate forms. 



FEEDING HABITS 



On the oats and wheat the insects locate mainly on the stems and on the 

 lower portions of the leaves. Only small plants could be used in the 

 experiments; and an occasional insect might be found feeding on any 

 portion of the plant, except that little tendency to locate at or below the 

 surface of the ground was noted during the season of 191 5. It may be, 

 however, that during hot, dry seasons the insects would prefer such 

 locations. 



1 This apparent discrepancy is due to the fact that late alate forms occurred only in those lines descended 

 from spring migrants of the fourth generation. 



2 Baker, A. C, and Turner, W. F. morphology and biology of the green apple aphis. In Jour. 

 Agr. Research, v. s, no. 21, p. 955-994. 4 fig-, pl- 67-75. 1916. 



