BULLETIN No. 177. 



DEPARTMENT OF ENTOMOLOGY. 



POTATO PLANT LICE AND THEIR CONTROL. 



BY W. S. EEGAN. 



Economic Importance op the Pest. 



Potato plants among other crops have suffered severely from the- 

 attacks of plant lice during the present summer. The extent of injury- 

 has varied considerably according to the infestation. Some potato 

 patches with a mild infestation have shown little injury, and the loss in 

 yield from this source will be negligible. In other fields, judging from the 

 extent to which the tops have been killed, the crop will suffer a loss of 

 from 10 to 50 per cent., and in some instances the destruction has been 

 so complete that it will hardly pay to harvest the crop. 



The potato plant louse (Macrosiphum solanifolii Ashm.) is not a new 

 insect to this section, but conditions appear to have been ideal during the 

 spring and early summer for its multiplication to such numbers as to 

 cause devastation in many places where no measures were taken to check 

 it. Nor has injury by this pest been exceptional in Massachusetts this 

 season. Reports from Connecticut, New York, New Jersey, Maryland, 

 Virginia and Ohio indicate that the potato crop of these States has suf- 

 fered equally as much; and in some of these States, in addition to killing 

 the potato plants in many localities, these lice were becoming dangerously 

 abundant on tomatoes. The potato crop of Maine and Canada has also 

 been severely curtailed during some years in the past due to these pests. 



In Massachusetts injury to potato plants by plant lice became evident 

 during the second week of July, and rapidly increased in severity until 

 the latter part of the month and early August, when no progressive 

 injury could be noticed, and an examination of previously badly infested 

 fields showed these insects present only in very small numbers, and cer- 

 tainly not numerous enough to cause further material injury this season. 



This indicates a period of about three to four weeks' time when the 

 plajit lice are dangerously prevalent upon potato plants, and reports 

 from other sections, as well as the past history of outbreaks of this pest, 

 indicate that this is about the length of time, dating from their first ap- 



