134 EXPERIMENTS IN DESTROYING BLACK-FLIES 



ment the cattle in the pasture, and pester the farmer in the 

 field." 



This fact that the black-flies of a locality usually develop in 

 that vicinity, and are comparatively easy to find in their breed- 

 ing-grounds offers the opportunity for so reducing their 

 numbers, if we can kill them in their breeding-places, that 

 they will no longer be troublesome. 



In the resort regions of northern New Hampshire the black- 

 flies have long been recognized as among the most annoying 

 pests for the summer visitors. I have had from time to time 

 appeals from hotel managers for help in subduing the insects, 

 but until recently have had to confess that I knew of no prac- 

 tical solution of the problem. For several years I have had 

 under observation a colony of black-fly larvae living on the flat 

 rocks of the outlet to our college reservoir, shown in the pic- 



Larva of Black-fly. Magnified. 



ture on the inside cover of this bulletin, and have often tried to 

 discover effective means of killing them. 



When studying the recent literature concerning mosquito 

 remedies, the property of Phinotas oil which leads it to 

 sink to the bottom in water led me to think that possibly 

 here we had an agent for destroying black-fly larvae. In 

 order to test the theory I sent the assistant entomologist, Mr. 

 A. F. Conradi, in June, 1903, to Dixville Notch, New r Hamp- 

 shire, where these pests have for many years been especially 

 troublesome, with specific instructions to find the breeding- 

 places of the flies, and to try the effect of the Phinotas oil with 

 which he was provided. 



The Dixville Notch region was peculiarly favorable as to 

 situation for an extended experiment in subduing black-flies, 

 for it is a comparatively small area surrounded by mountains 

 over which no flies from other localities would be likely to 



