Plant-Lice 



the time they have developed the first issuing females will have 

 settled upon the plum trees and will have given birth partheno- 

 genetically as before to a generation of wingless individuals 

 which comprise the true females not the virgin females as 



Fig. 1 66. Phorodon humuli : return migrant. (From Insect Life.) 



before but the true females which must be fertilized by the 

 males. So that, by the time the winged males have developed 

 from the hop and fly back to the plum we have this generation 

 of wingless sexual or true females awaiting them. Impregnation 

 then takes place, the males die, and these wingless sexual females 

 give birth to the winter eggs. 



268 



