PLANT LICE 



Heretofore, the species has remained on the apple trees, 

 but now the winged ones are possessed with a desire for a 

 change, a complete change both of scenery and of diet. 

 They leave the apples, and when next discovered they are 

 found to have established themselves in summer colonies 

 on those common weeds known as plantains, and mostly 

 on the narrow-leaved variety, the rib-grass, or English 

 plantain (Fig. 99). 



As soon as the mi- 

 grants land upon the 

 plantains they give birth 

 to offspring quite unlike 

 themselves or any of the 

 preceding generations. 

 These individuals are of a 

 yellowish-green color and 

 nearly all of them are 

 wingless (Fig. 99). So 

 well do they disguise 

 their species that ento- 

 mologists were a long 

 time in discovering their 

 identity. Generations of 

 wingless yellow females 

 now follow upon the 

 plantain. But a weed is 

 no fit place for the stor- 

 age of winter eggs, so, 

 with the advent of fall, 

 winged forms again ap- 

 pear in abundance, and 

 these migrate back to the 

 apples. The fall mi- 

 grants, however, are of two varieties: one is simply a 

 winged female like the earlier migrants that came to the 

 plantain from the apple, but the other is a winged male 

 (Fig. 100 A). Both forms go back to the apple trees, and 



[169] 



Fig. 99. The rosy apple aphis on nar- 

 row-leaved plantain in summer; above, a 

 wingless summer form (enlarged) 



