178 The Potato 



certain seasons, these insects become very numerous and 

 their depredations check the growth of the vines con- 

 siderably. The wounds made by the beaks of the aphids 

 often admit fungi and indirectly result in greater injury 

 than the work of the insect alone. 



The potato aphid passes the winter in the egg stage, 

 the eggs being attached to weeds. In the early spring, the 

 adult insects are to be found feeding on the succulent tips 

 of rose bushes. In July, the aphids migrate to potato 

 fields and start feeding there. The potato seems to be an 

 ideal food for this insect, for it increases in numbers very 

 rapidly, a single female often producing over fifty young 

 in two weeks. Late in August or early in September, 

 the lice leave the potato vines and go to rose bushes or 

 other food plants. Here they produce several more 

 generations of young. The last generation of the year 

 consists of wingless females and winged males. The 

 females lay the over-wintering eggs on the shepherd's 

 purse, potato, and other food plants. 



Control. — There are certain natural agencies of control 

 over these insects which frequently make them of little 

 consequence. Among these are cold weather, frequent 

 rains, parasitic fungi and insects, and various predacious 

 insects. These factors cannot be relied upon, however, 

 to keep the pest in check every year. Fall plowing will 

 turn under many weeds and old leaves on which the eggs 

 have been laid. It has also been suggested that the 

 farmer burn the dead vines in the fall in order to destroy 

 the eggs. The adult insects can be killed by using any 

 good contact insecticide like one of the tobacco extracts, 

 kerosene emulsion and the like. Spraying is usually only 

 resorted to when the insects become very troublesome. 



