LIFE HISTORY. 15 



Table I . — Rate of deposition of young by winged migrants of the hop aphis from prune trtes. 





Date and number deposited. 



Total. 



Became winged. 



May 28. 



May 29. 



May 30. 



May 31. 



June 1. 



June 3. 



Mav 28 - - 



1 

 2 

 1 

 2 



4 

 2 

 3 



4 



1 



1 







7 



Do - - 



1 







5 



Do 







1 



1 

 1 



1 



5 



Do 



1 





8 





1 



1 









2 



3 











1 



























4.3 











1 







The data in Table I were obtained by isolating nymphs, taken 

 from the prune trees, upon clean prune leaves in covered jelly glasses. 

 When the winged insect appeared 

 it was immediately placed upon a 

 hop leaf. The deposited young 

 were removed daily. 



Fig. 4. — Head of hop aphis, showing frontal tuber- 

 cles. Greatly enlarged. (Original.) 



Fig. 5. — Head of melon aphis (Aphis gossypii). 

 This aphis is frequently found on hops. Note 

 differences in head from that of hop aphis. 

 Greatly enlarged. (Original.) 



These young deposited by the 

 winged aphides are wingless par- 

 thenogenic insects (PL II, fig. 1). They have the characteristic frontal 

 tubercles (see fig. 4, in comparison with fig. 5) and vary in color from 

 watery white to green. The very young insects and those that have 

 just mo] ted are very light, while the older ones may be quite green. 



RATE OF GROWTH. 



These young aphides grow very rapidly, molt four times, and 

 immediately after the fourth molt commence depositing their young, 

 as shown in Table II. 



Table II. — Stages in the 



development of the wingless viviparous fema 



le hop aphis. 



No. 



De- 

 posited. 



First 

 molt. 



Second 

 molt. 



Third 

 molt. 



Fourth 

 molt. 



Com- 

 menced 

 depositing 

 young. 



Total 

 days. 



l 



June 11 

 15 

 15 

 16 

 18 

 18 



June 13 

 17 

 18 

 19 

 21 

 22 



June 15 

 20 



21 

 21 

 23 

 24 



June 17 

 23 

 23 

 23 

 26 

 26 



June 19 

 25 

 26 

 25 

 28 

 28 



June 20 

 27 

 27 

 27 

 29 

 29 



9 



9 



12 



3 



12 



4 



U 



o 



12 



6 



12 







