ii ~-r.-r,^^r ^<r^„ )> 



70 THE SPRING GRAIN-APHIS OR GREEN BUG. 



Mr. T. D. Urbahns, of this bureau, carried on a series of check 

 experiments at Dallas, Tex., in 1909, starting in March and ending in 

 the fall. (See table, pp. 64-69.) As will be observed, and for 

 reasons explained farther on, he did not obtain the sexes. By these 

 experiments the maximum number of generations was secured as 

 described under rearing methods (p. 51). The maximum number of 

 generations in 1908 among the five series of continuous generations was 

 21 and, as shown below, occurred in series I of first-born; the mini- 

 mum being 6 in series FF of the series of last-born. The complete 

 series are as follows: Series B, maximum (from first-born), 20 genera- 

 tions; series BB, minimum (from last-born), 9 generations; series C, 

 maximum (from first-born), 18 generations; series CC minimum 

 (from last-born), 8 generations; series F, maximum (from first-born), 

 16 generations; series FF, minimum (from last-born), 6 generations; 

 series G, maximum (from first-born), 19 generations; series GG, 

 minimum (from last-born), 9 generations; series I, maximum (from 

 first-born), 21 generations; series II, minimum (from last-born), 10 

 generations. If all of these be added, we will find the average to be 

 13.6 generations. This will represent the approximate number of 

 generations for the year. In 1909 there were two series reared, A and 

 B, both resulting the same. Series A, maximum (from first-born), 

 18 generations; series AA, minimum (from last-born), 7 generations; 

 series B, maximum (from first-born), 18 generations; series BB, 

 minimum (from last-born), 7 generations. The average for these 

 two lines would give 12.5 generations, a little lower average than at 

 Richmond, Ind. 



Mr. Urbahns carried out one series of first-born generation experi- 

 ments at Dallas, Tex., in 1909, from which he obtained only the 

 maximum number of generations. He began March 31 and finished 

 November 3. In this time he reared through 25 generations but did 

 not ascertain the sexes, neither was he successful in finding them in 

 the fields. 



It appears that the species will vary in the number of generations 

 produced from individuals hatched the same day, and from the off- 

 spring kept under the same conditions throughout the year. This 

 will readily be understood when the amount of individual variation 

 'in molting is considered. 



AGE AT WHICH FEMALES BEGIN REPRODUCING. 



The age at which females begin reproducing varies greatly between 

 spring and summer and between fall and summer; as between spring 

 and fall the age is very much the same. At Richmond and La Fayette, 

 Ind., Toxoptera begins reproducing at from 5.9 to 16 days between 

 the middle of May and latter part of September. From the time of 

 hatching until the middle of May the period is from 20 to 27 days; 



