INSECTS 



the tree depends for a proper start of its spring growth, is 

 stunted and yellowed. Now is the time for the orchardist 

 to spray if he has not already done so. 



The entomologist, however, takes note that all the 

 young aphids on the apple trees are not alike; perhaps 

 there are three kinds of them in the orchard (Fig. 95), 

 differing slightly, but enough to show that each belongs 

 to a separate species. When the first buds infested are 



ABC 



Fig. 95. Three species of young aphids found on apples in the spring 



A, the apple-grain aphis, Rhopalosiphum prunijoliae. B, the green apple aphis, 



Aphis pomi. C, the rosy apple aphis, Anuraphis roseus 



exhausted, the insects migrate to others, and later they 

 spread to the larger leaves, the blossoms, and the young 

 fruit. The aphids all grow rapidly, and in the course 

 of two or three weeks they reach maturity. 



The full-grown insects of this first generation, those 

 produced from the winter eggs, are entirely wingless, and 

 they are all females. But this state of affairs in no wise 

 hinders the multiplication of the species, for these re- 

 markable females are able of themselves to produce off- 

 spring (a faculty known as parthenogenesis) , and further- 

 more, they do not lay eggs, but give birth to active young. 

 Since they are destined to give rise to a long line of sum- 

 mer generations, they are known as the stem mothers. 



One of the three aphid species of the apple buds is 

 known as the green apple aphis (Pig. 95 B). During the 



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