BIOLOGICAL STUDIES ON THREE APHTDID^. 125 



light, thus giving conditions probably most favorable to the optimum 

 development of the aphis. As soon as the plant began to wilt it was 

 replaced by a fresh one, the aphides being transferred thereto by 

 means of a camel's-hair brush. 



During the life cycle of this aphis there appear five different forms, 

 namel3% winged viviparous females, wingless viviparous females, ovi- 

 parous females, males, and eggs. Briefly, the life history is as fol- 

 lows : From the eggs, which have been found hatching in the field be- 

 tween April 8 " and May 22, from 10 to 22 generations may follow. 

 These generations are all viviparous from spring until the latter part 

 of September or in October, according to conditions of temperature, 

 etc. The last generation of the season is known as the oviparous gen- 

 eration, and consists of males — wingless only, so far as known — and 

 oviparous wingless females. The males and females pair, and the 

 females lay eggs, usually during the months of October and Novem- 

 ber, the eggs not hatching until the following spring. 



Now follow^s a detailed account of the life history as worked out 

 by me in 190G. Eggs collected at Elliott, 111., April 12, 1906, in the 

 nests of the common brown ant {Lasius niger L., var. aniericanus 

 Emery) were placed in a cage in our insectary April IG. They were 

 first noticed to be hatching April 17. Young aphides hatching April 

 18 and 19 were placed on corn roots in the previously-described vials, 

 and two lines of generations were thus started, both of which were 

 carried through to the Qgg in the fall. These stem mothers — that is, 

 the aphides hatching from the Qgg — produced their first young May 1 

 and J:, respectively, and their last young May 18 and 14, respectively. 

 Taking the first young of the first young all the way through the 

 series, 22 generations were obtained, counting the oviparous genera- 

 tion as the last. (See Tables I and II.) 



«In 1906 Mr. E. O. G. Kelly, a field assistant of the State entomologist of 

 Illinois, seaix'hed for eggs and young of A. maidi-radicis in the fields, beginning 

 the 1st of April. He did not find eggs until April 12, and on April 17 he found 

 the young stem mothers in the field. The following year Mr. Kelly first found 

 eggs March 24 (these hatched in the insectary March 26), and young stem 

 mothers were found in ants' nests as early as March 29. April 1,5 he found the 

 young with their beaks inserted in old corn roots, this probably being occasioned 

 by the fact that large numbers of the weeds upon which the aphis usually feeds 

 at this season had been killed by the very cold weather of the preceding week. 



