POTATO PLANT LICE AND THEIR CONTROL. 137 



Life Cycle of the Potato Louse. 



Numerous observations have been made on the life cycle and habits 

 of the potato louse (Bulletin No. 147, Maine Agricultural Experiment 

 Station), but many important details are yet to be learned. Infestation 

 of potato plants during the late spring and early summer is accomplished 

 by a migration of the plant lice, either by flight or by crawling from neigh- 

 boring vegetation. These new arrivals are all females, and begin at once 

 to feed upon the sap of the plants. These females lay no eggs, but in a 

 short time produce living offspring, which are the first of a long series of 

 females, and these likewise in the course of eight to ten days produce 

 living young. Plant lice are prolific breeders, a single female often pro- 

 ducing as many as 20 young per day. It is, therefore, not astonishing 

 that they should multiply so rapidly and cause such devastation in a 

 comparatively short time. No males or egg-laying females ever occur 

 upon potato plants. The first few generations may be wingless, or at 

 any time winged individuals may appear and fly away to seek fresh 

 plants for their own feeding and for their progeny, thus causing a more or 

 less even infestation of potato fields. 



After spending a few weeks or months upon potato plants, winged 

 individuals called "fall migrants" appear and leave the potato plants 

 for winter hosts, — plants of the same kind as those from which the 

 spring migration took place to the potatoes. As previously stated, the 

 migration to the winter hosts here in Massachusetts takes place probably 

 to some extent during the latter part of July, but mainly during August, 

 the exact time, however, varying according to seasonal fluctuations of 

 temperature and moisture, and the condition of the potato plants. The 

 early drying out or dying of the potato tops will, no doubt, hasten the 

 appearance of "fall migrants," regardless of whether the drying out is 

 •due to injury by the plant lice or to other factors. 



Observations by Miss Edith Patch, State Entomologist of Maine, seem 

 to indicate that buckwheat and shepherd's purse are among the winter 

 hosts sought by these insects. The migration to the winter host plants 

 is followed by the production of winged males and wingless, egg-laying 

 females. These females lay glistening brownish black eggs upon the 

 leaves and stalks, and in this stage the winter is passed. 



Control Measures. 



Practical Considerations and Fundamentals of Control. 



Under the topic "Manner of Feeding and Nature of Injury," discussed 

 on an earlier page, it was pointed out that plant lice obtain their food by 

 piercing the host plant and sucking the juices from within, no feeding 

 being done on the outer surface. Therefore any poison, such as arsenate 

 of lead or Paris green, which is sprayed over the foliage and must be 

 eaten in order to be effective, would be absolutely useless against plant 



