a4 



PAPERS ON AfHIDIDiE. 



As will be noticed by ref erriiij^^ to figure 1 5 the fii-st generation ex- 

 tended over a period of 39 days, from April 22 to May 31 ; the second, 

 60 days; the third, 54 days, etc.; and the eighth generation, which 

 includes the last generation of tlie last-born series, being the longest, 

 a period of 128 days. It is interesting to note that on May 4 indi- 

 viduals of tlie fii-st 2 generations coexisted in the insectary ; on June 4, 

 3 generations; on July 4, 5 generations; on August 4, 8 generations, 

 or from the fourth to the eleventh; on September 4, 10 generations, oi' 

 from the sixth to the fifteenth; and on October 4, 11 generations, or 

 from the seventh to the seventeenth. Also, it wiU be observed that 

 sexual generations occurred in the last 10 generations, from the eighth 

 to the seventeenth inclusive, thus, with the additional data previously 

 reported by W(>bster and Phillips, and by the writer, thoroughly dis- 



KiG . 1.5.— Diagram showing periods and succession of generations in the yellow clover aphis, La Fayette, 



Ind., 1913. (Original.) 



proving the theory held by some that the sexual forms appear neces- 

 sarily in a certain definite generation. 



Our records show that the first oviparous females were observed in the 

 experimental cages early in October, they having been born Septem- 

 ber 25, and our field records prove that the sexual forms may be pro- 

 duced even earher than this. As has been inferred, the sexual forms 

 seem to appear after the earliest weather conditions indicative of win- 

 ter, although occasionally viviparous females have been observed 

 until killed by cold weather. It was a usual occurrence for the same 

 female to produce young part of which were viviparous and part 

 oviparous. 



Again referring to Tables I and II it wiU be seen that the immature 

 stage varied from 6 to 16 days, depending on the temperature; the 

 average for the year, in the 1913 series, being 9.1 days. The pro- 

 ductive period, from birth of first young to birth of last young, like- 



