HEMIPTERA: THE TRUE BUGS 93 



numbers of the plant lice increase, the ants extend the 

 burrows to provide for them. The ants continue thus to 

 look after the needs of the aphides throughout the summer 

 months. In autumn, however, a still more interesting thing 

 takes place, for at this time an egg-laying brood of aphides 

 is developed and the small blackish eggs are taken by the 

 ants far down in their underground nests, where the eggs 

 are cared for throughout the winter. When the eggs hatch 

 early the following spring, the young plant lice are carried 

 by the ants, generally to the roots of some grass-like weed, 

 there to start the new season's brood, which will be trans- 

 ferred later to the roots of the young corn plants. 



In a case like that of the Cornroot Aphis, where the 

 eggs of the insect pass the winter in the cornfield, rotation 

 of crops is the best means of reducing injury by the pest. 

 It is fortunate that there are great numbers of enemies of 

 aphides in general, for otherwise it would probably be im- 

 possible to grow many crops now produced. Many birds 

 feed freely upon the eggs and later stages of aphides, while 

 vast numbers of predaceous and parasitic insects develop at 

 their expense. The insecticides that are most effective in 

 destroying plant lice are kerosene emulsion, whale-oil soap, 

 and various decoctions and extracts from tobacco stems. 



ELM LEAF AFFECTED BY APHIDES 



