BIOLOGICAL STUDIES ON THREE APHIDID^. 



149 



Although no exact figures can be given as to the minimum number 

 of generations (breeding ahvaj^s from the last l)orn of each genera- 

 tion), still, from my experiments, it may be definitely said that there 

 were not more than D generations after June 26. The aphides were 

 kept in the unheated insectary greenhouse, and thus the temperature 

 was approximately the same as tliat out of doors. The last date 

 recorded for living aphides was December 21. The immature stage 

 covered from 5 to 24 daj-s. varying wdth the season ; thus, in the 

 w^armer parts of the year, from the last of June until the middle of 

 September, the average for 30 experiments was CO days, wdiile from 

 the middle of September until the 1st of November for 10 experi- 

 ments the average was 12.8 days. The average for the entire 40 

 experiments was 8.1-1- days. (Table VIII.) 



The length of the period for producing young varied up to 48 

 days, with an average, for the entire series of experiments, of 19 

 days. The mother usualh^ lived a few days after the birth of her 

 last young. The entire length of life averaged 31.6-|- days. The 

 average number of young produced by a single aphis, in the 33 ex- 

 periments of which record was kept, was 33.5-|-, while the largest 

 number was G5. Individual aphides in some cases produced as many 

 as 6 or 8 young per day, but the usual number was 2. The number 

 of molts is invariably 4. Table IX gives the records of a few indi- 

 viduals, showing the number of molts and the time between each molt. 



Table IX. — Periods of molts of ApJiis maidis, viviparous generation, 1906-7. 



DatP of birth. 



Age at ! Age at 

 first second 



molt. molt. 



Age at 

 third 

 molt. 



Age at 

 fourth 

 molt. 



Age at 

 birth of 



first 

 young. 



July 23, 1905. . . 



Do 



July 24, 190.5... 

 Jidy 27, 1905. . . 

 .August 4, 1905. 

 Augusts, 1906. 

 August 14, 1906 



Days. I Days. 



2 ! 



li 



Days. 



Days. 



Days. 



DESCRIPTIONS. 



Aphis )naidis Fitch. 



VIVIPAROUS GENERATION. 



Before first molt and less than 1 hour old. — General color light 

 pea-green. Eyes red. AntennjB transparent, only 4 distinct seg- 

 ments, or 5 if the filament lie counted, the third having a slight con- 

 triction, which is the beginning of a division of that segment. Legs 

 transparent. Cornicles vasiform. Measurements: Length of body, 

 0.545 mm. ; width, 0.236 mm. 



After first molt and 2Jf.-.'i8 hours old. — General color between pea- 

 green and chromium-green. Eyes red. Antennae as in the earlier 



