3OO LOUISE H. GREGORY. 



viduals produced 1,149 young, 9.7 per cent, of which were 

 winged. The starved mothers had about three times as many 

 winged young as the control. Since all the families were sub- 

 jected to the same conditions of temperature and humidity, the 

 variation in the results must be due to the only factor in which 

 they differ, namely the food supply. 



Temperature undoubtedly may effect the production of wings 

 as Ewing 1 has shown in his experiments with Aphis avence. He 

 found that by keeping the temperature constant at 65 F., he 

 could prevent the appearance of any winged forms. At lower 

 and higher temperatures winged forms appeared. These results 

 might be interpreted as due not to the direct effect of tempera- 

 ture on the development of wings but on the growth of the 

 plants or the food supply and thus indirectly affecting the me- 

 tabolism of the individuals. 



If the summer experiments are compared with those in the 

 winter, it will be observed that the percentage of winged forms 

 is less in both starved and control lines. However the percentage 

 of increase in number of winged forms in the starved lines 

 remains constant. In the summer as in the winter there are 

 three times as many winged young in the starved lines as in the 

 control. I see no reason why the temperature might not have 

 been effective indirectly in the lessening of the wing production 

 in both starved and control summer lines. The atmosphere of 

 the greenhouse was practically constant, while the summer 

 experiments were carried on out of doors and were subject to 

 all the daily changes in temperature and moisture. The actual 

 difference in the development of wings at any one time must 

 have been due to the difference in food supply, temperature 

 having no part. I believe that if aphids were starved for long 

 periods and kept at a constant temperature of 65 F., Ewing's 

 optimum temperature, winged individuals would appear. 



Overcrowding on the plants has been suggested as a possible 

 cause of wing development. In nature this might be true, 

 the results however being due to a lessening of the food supply. 

 In my experiments there was no overcrowding as the young were 



1 Ewing, H. E., " 87 Generations in Parthenogenetic Pure Line of Aphis avence," 

 BIOL. BULL., Vol. XXXI., No. 2, 1916. 



