Dec. IS, I9I9 Apple-Grain Aphis 315 



reproduction period was 15.3 days, varying between 10 and 23. The 

 greatest average daily production was 5.8 young and the lowest 3.39, 

 the daily average for the six insects being 4.44. 



TOTAL LENGTH OP LIFE 



One insect of the spring apterous form lived for 42 days. The average 

 length of life, however, was only 30.8 days, and two aphids died when 

 only 21 days old. 



SPRING MIGRANT 

 LENGTH OF NYMPHAL LIFE 



This period varied from 8 to 12 days, the average for 22 insects being 

 8.36 days. The variation in this period was closely connected with the 

 variation in mean temperatures. The time occupied by the nymphal 

 stage was divided rather evenly between the four instars concerned, 

 the final instar being a little longer than the others. The final instar of 

 the spring migrants was usually about one day longer than that of the 

 apterous insects born the same day. 



SPRING MIGRATION 



In 1 91 5, at Vienna, Va., migration began about May i and continued 

 till about June 7. No general migration occurred with this species either 

 in 1914 or 1915. The alate insects left the apple singly a day or two 

 after having become adults. Migrants could not be found on grasses in 

 any abundance, though single individuals were taken here and there in 

 the fields. No attempt was made to determine the species of Graminaceae 

 upon which this insect spends the summer. In the experiments it lived 

 easily on both oats and wheat, the former being used more generally be- 

 cause it was found to be easier to handle. 



REPRODUCTION 



Complete data covering reproduction were obtained with 21 insects. 

 The average number of young produced per mother was 13.5. The 

 smallest number produced by one insect was 9 and the largest 20. 

 Ten insects produced from 9 to 13 young each. The average daily 

 production was 0.85 per mother. These spring migrants produced 

 very irregularly, often passing as much as 3 or 4 days without giving 

 birth to any young. The usual number produced on one day, taking 

 into account only the days during which reproduction actually occurred, 

 was about 3. One insect produced 10 young within 24 hours. 



TOTAL LENGTH OF LIFE 



The average total length of life for the spring migrant was a little 

 over 27.6 days. The shortest for one insect was 15 days. All other in- 

 sects lived over 20 days. One was fixed after having lived for 37 days. 

 134796°— 19 2 



