PHYSIOLOGY OF WING DEVELOPMENT IN APHIDS. IO7 



been made. A part of my experiments, and also those of Pro- 

 fessor Clarke, were carried on in our laboratory where a nearly 

 uniform temperature was kept throughout a period of several 

 days. A larger part of my work was done in an old greenhouse 

 where the change of temperature between day and night was 

 exceedingly great. I have also done a part of my work out of 

 doors. In all of these cases, only a very few of the winged 

 aphids appeared on the twigs charged with any of the non-wing- 

 developing substances. Professor Clarke stated that he had 

 subjected aphid-infested twigs charged with distilled water to a 

 sudden change of temperature from 80 F. to 30 F., and had 

 observed no effect on the wing development. These observa- 

 tions, therefore, establish the fact, I believe, that changes in 

 temperature have no effect on the production of winged forms. 



The popular conception that the approach of cold weather 

 makes winged aphids appear may be explained in the following 

 manner. Plants mature either at the time when the cold weather 

 sets in or previous to that period. They also manufacture, 

 through the agency of their leaves and under the influence of 

 sunlight, starch, which at this maturing period is changed to 

 sugar and stored away in other parts of the plant. This sugar 

 is the most common wing-developing substance, as we have 

 seen. Therefore, the aphids produce wings at the approach of 

 cold weather, not because of the low temperature, but because of 

 the presence of sugar in the plant tissues at that time. 



2. Wilting of the Plant. Professor Woodworth has pointed 

 out that when the plants, especially cabbages on which he has 

 made extensive observations, are badly infested with aphids 

 and begin to wilt, there was a decrease in the birth rate of the 

 insects and a "spontaneous appearance of the aphids with wing- 

 pads was noticed." His explanation of this phenomenon is 

 that the wilting of plants probably causes an effect similar to 

 that produced by the magnesium salts, that is, it makes it 

 possible for the wing-buds to have an even chance with the rest 

 of the body to develop. Under more favorable conditions, he 

 suggests_that the growth of the wing-fundaments might be re- 

 tarded on account of the faster growth of the other parts of the 

 body. A morphological study bearing upon this point is pre- 



