314 ANIMAL AGGREGATIONS 



effect of parentage upon wing production to see if there is an innate 

 cycle which causes winged forms to appear at certain intervals. 

 During a period of 12 months of continuous work, 59 complete 

 generations were reared without the appearance of winged forms, 

 except in 3 generations when the aphids became crowded. These 

 results are supported by other data and indicate that with this 

 species of aphid there is a normal tendency to be wingless and that 

 the production of wings depends upon environmental influences 

 rather than on an innate cycle, as many have thought (Shull, 1929). 

 Reinhard's experience with starvation supported that of previous 

 workers. He found that starvation of apterous parents increased 

 the number of alate individuals, while starvation of alate parents 

 did not affect the normal tendency of such animals to produce 

 wingless forms. 



Reinhard also found that with the species of aphid which he ob- 

 served, the appearance of its winged phase was not determined by 

 the temperatures to which the animals were exposed, nor by humid- 

 ity. Other workers (vide Shull, 1929) have found that temperature, 

 and Hght relations as well, do affect the appearance of winged aphids 

 of other species. Having cleared the way by these preliminary ex- 

 periments, Reinhard turned to more intensive experimentation upon 

 the effect of crowding upon wing production. 



In his long experiments, he found no winged forms except when 

 the plants were allowed to become crowded. Subcultures from this 

 experiment were made at different generations. The aphids were 

 isolated on uninfested plants, and they and their progeny were 

 undisturbed until a crowded condition resulted. In each case these 

 subcultures yielded alate aphids, even though the uncrowded main 

 experiment did not. The results of these experiments are summa- 

 rized in Table XXXVI. 



In another series of experiments wingless aphids of unknown 

 parentage were placed on uninfested plants and allowed to develop 

 crowded conditions. In 14 tests which are reported by Reinhard in 

 detail the history of 438 aphids is given. Of these, 221, or slightly 

 more than 50 per cent were alate; 5 winged aphids, or about 2 per 

 cent, appeared among the 243 individuals reared under conditions 



