34 



GENERAL ZOOLOGY 



Very many of our cultivated plants and trees are 

 subject to damage by these insects. On the apple trees 



Fig. 18. Aphid with wings. (Much enlarged) 

 From the Illinois State Natural History Survey 



the woolly aphis (Erioso'ma lanig'erum) may live either 

 on the roots beneath the ground or on the branches. 



In some species the eggs undergo 

 full development within the body of 

 the mother. In such cases the young 

 are born alive and fully formed. Re- 

 production in such instances is very 

 rapid. The food plant becomes so 

 completely covered that there is 

 scarcely standing room. An aphid 

 colony in the summer may consist 

 almost entirely of wingless females 

 (Fig. 19) which have the power of 

 producing generation after generation 

 of living young without fertilization. 



This form of reproduction is known as parthenogenesis. The 

 young so produced are females, and many of them are wing- 



Fig. 19. Wingless aphid 



From the Illinois State 

 Natural History Survey 



