Dec. IS, 1919 A p pie-Grain Aphis 321 



DURATION OP LARVAI, STAGS 



Fall migrants required from 14 to 17 days to attain maturity, this 

 being three or four days more than was required by their apterous sisters. 

 It is probable that the increased length of this period is due almost entirely 

 to the lower temperatures prevailing in the fall, this accounting not 

 only for the lengthening of the immature period of the apterous insects 

 but also for the further lagging of the alate form behind the apterous. 

 However, the fact that the fall migrant is much larger than the apterous 

 form (and than the summer migrant) may have an effect. 



REPRODUCTION 



Sixteen fall migrants produced an average of 5.9 young apiece, the 

 number varying from four to eight. In every case the mothers produced 

 all their young within a period of from 24 to 36 hours. In other words, 

 the mother produced them rapidly with no long resting period between 

 births. 



LONGEVITY 



The average total length of life of seven fall migrants was a little over 

 33X days. All the insects lived for some time after having finished re- 

 production, sometimes for as long as three weeks or more. One insect lived 

 for 26 days after reproduction had been completed, its total length of life 

 being 51 days. This short reproductive period followed by a prolonged 

 life of several days was found to prevail also among the fall migrants 

 of Anur aphis malifoliae Fitch. 



OVIPARA 

 LENGTH OF LARVAL STAGES 



The oviparous form matured very slowly in comparison with earlier 

 forms of the year, requiring a period of from 1 6 to 20 days to reach matu- 

 rity. It developed very irregularly, the amount of time spent in the 

 several instars not being at all uniform for the various insects. This 

 apparently was due to the fact that during especially cold periods the 

 insects became quiescent, and since no development could take place during 

 such a period the particular stage in which the insect was at the time 

 would be prolonged. 



MAI^E 

 DURATION OP LARVAL STAGES 



In our experiments all males required about 16 days to attain maturity. 

 This about equals the length of time required by fall migrants bom late 

 in the season. 



