28 JOURNAL OP ECONOMIC ENTOMOLOGY [Vol. 3 



out with a cup in the rapids by a man wading down stream would 

 destroy the larva effectively. The larvce are found almost entirely 

 on the rocks where the water flows over them very swiftly and breaks 

 into rapids or spray. Rocks in smooth running water have very few 

 larvaj upon them. In the preliminary experiments a net was stretched 

 across the JMoose River, a small stream 10 to 20 feet wide, and 

 the water was oiled for a distance of 100 yards above the net. The 

 man applying the oil can walk nearly as fast as it floats down 

 stream and the fish descend the stream ahead of the oil. Where the 

 fish were caught in the net many of them were overcome by the oil, 

 but as it passed on and the water cleared up within 15 or 20 minutes, 

 all revived and showed no subsequent ill effects. This experiment 

 was repeated three times in which individual fish were overcome each 

 time, but survived with no ill effect. 



After these experiments it was determined to oil a considerable 

 stretch of the stream, which was done in the same way. This applica- 

 tion was entirely effective in destroying the larvae, but unfortunately it 

 resulted in killing a considerable number of the fish, due to the fact 

 that the volume of oil was such that the fish descending the stream 

 with it were subjected to it for too long a time. From our previous 

 experiments we feel certain that had nets been stretched across the 

 stream so as to catch the fish and so that they would not have been 

 subjected to the oil for over 15 or 20 minutes, no trouble of this 

 kind would have ensued. Our observations also lead us to the opin- 

 ion that the oil might be applied much more economically by the use 

 of a knapsack sprayer and a nozzle, preferably a Bordeaux nozzle, by 

 which the oil could be applied directly to the worst affected rocks in 

 a spray which could be directed immediately on them. This would 

 use much less oil and would consequently have less effect on the fish. 

 The method of merely throwdng the oil in the stream with a cup forms 

 an emulsion of the whole volume of water in the stream. The oiling 

 vras carried on both in the river, wdiich has a gradual fall, and also 

 in Cold Brook, which descends the mountain side very rapidly over 

 large stones as shown in plate 2. The application was equally effective 

 under both conditions. The numbers and position of the larva on the 

 large stones in Cold Brook are indicated by plate 3, in which they 

 are somewhat indistinct owing to an inch or two of water flowing 

 over them. 



From these experiments and observations we are led to believe that 

 the destruction of black flies in the resort regions of our mountains is 

 entirely as feasible as the control of mosquitoes in low country such 

 as the vicinity of New York and New Jersey. To work out practical 



