16 THE SPRING GRAIN-APHIS OR u GREEN BUG.'* 



an average of 34.25 young to each individual. While too small a 

 number of individuals was taken to make the result conclusive, it 

 plainly indicates that fecundity is greatest among the "wingless 

 individuals. 



AVERAGE NUMBER OP YOUNG PRODUCED DAILY. 



By "the average daily number of young produced" is meant the 

 daily average for the reproductive period only of each individual. 

 At Richmond and La Fayette, Ind., the average number of young 

 produced daily for those born from March to the middle of June is 

 1.9; the daily average for those born from the middle of June to the 

 middle of August is 1.7; the daily average for those born after the 

 middle of August is 1.2. These figures, of course, include only those 

 individuals in the generation experiments. The average number of 

 young produced daily for the entire year is 1.6. The final average 

 remains the same when all individuals are considered, irrespective 

 of generation experiments. 



From the above it will be seen that the daily average is greatest 

 in the spring, the summer coming next, and the fall last. This 

 corresponds also to the average total number of young for each indi- 

 vidual for these periods. 



Mr. Urbahns found that the average number of young produced 

 daily at Dallas, Tex., for those individuals that began reproducing 

 during December and Januarv was 1.5: the dailv average for those 

 that began reproducing during April and May was 3.4; the average 

 for those that began reproducing during June, July, and August was 

 2.1; the average for those born after August was 2.5. These averages 

 will be seen to agree proportionately with the average number of 

 young produced by a single individual during these periods, with the 

 exception of the daily average for December and January, which is 

 considerably lower. The average daily number of young for the 

 entire breeding season for which Mr. Urbahns has any data is 2. 



From the above data it will be seen that the average daily number 

 of young for Texas is far above the average for Indiana. This can 

 probably be accounted for from the fact that the reproductive 

 period is much longer in the North and the young are distributed 

 over a longer period. Also the average number of young for each 

 individual is greater in the South. 



SEXUAL FORMS. 



The first young of the sexes in Indiana are apparently born the 

 last week in September, the first adults oftentimes appearing as early 

 as the first week of October. The adults can be found from this time 

 on until December, or until they are killed off by extreme cold. 



The males can easily be distinguished by their small size. The 

 oviparous females (fig. 9) can be readily distinguished without a hand 



