394 



THE MONTHLY BULLETIN. 



October the developmental period increased again to 25 days, in November to 5 

 weeks, while in the winter months it was prolonged to 25 months. The rate of 

 growth is at all times closely dependent on the condition of food coupled with 

 influences of temperatures. The first instar is invariably the longest ; generally 

 it is nearly twice as long as any of the other three larval instars, which are of 

 about equal length, but frequently in the breeding dishes the young aphids had 

 trouble finding desirable locations and lost considerable time in becoming settled, 

 thereby prolonging the period of the initial stage to a considerable extent. Once 

 the larva? became settled they did not move away unless the quality of their food 

 deteriorated. 



All attempts to colonize apple or cork elm roots failed, yet the apple woolly 

 aphis was raised on pear roots, French, Japanese and Kieffer; but it appeared that 



■te 





/#* 



Fig. 131. Eriosma pyricola : old dry gall on cork elm 

 leaf. (A. C. Baker.) 



they did not develop as successfully on these as upon apple roots, and no swellings 

 were caused to form on the pear roots. The pear woolly aphis was raised with as 

 good success on Japanese and Kieffer roots as upon French. In most cases it 

 failed to feed on quince roots. 



There are as many as ten wingless generations a year on pear roots. Compared 

 with other aphids the rate of reproduction is slow, yet this rate does not compare 

 unfavorably with that of the apple woolly aphis. Baker (5) found that the wingless 

 females of this species deposited on the average 30 young at the rate of 3 per 

 diem. The pear woolly aphis feeding on roots somewhat below the average in 

 quality averaged 40 young at the rate of 1.6 per diem. 



