13 



insects tioatiug upon the surtace of the water was made over a restricted 

 portion, aud from this count the entire insect surface contents of the 

 pool was estimated, with the following- result: 



Entire number of dead insects floating on the surface 7, 400 



Number of mosquitoes 370 



Number of Epirrita inclinata Walker — a small Geometrid moth 148 



Number of Heterophleps iriguttata H S. — another small Geometrid 42 



Number of Clirysops Mlaris O. S. — a common gad fly of the region 27 



These were the most conspicuous. Tlie others were mainly minute 

 Nematocerous Diptera, although there were still a large number of 

 small Heterocerous Lepidoptera, a few aquatic Ooleoptera^ — the largest 

 species being the Dytiscid Agabiis gagafes Aube — and also a few speci- 

 mens of Cryptocerate Heteroptera. 



It is difficult to say how certain of the non-aquatic species, particu- 

 larly the Lepidoptera and the Chrysops, happened to be caught. They 

 may have visited the pool to drink or they may liave been attracted to 

 its shining surface. 



The observation, it seems to me, possesses interest not only as prov- 

 ing definitely the efhcacy of the remedy and as showing that adult 

 mosquitoes are killed as well as their early stages, but also as afford- 

 ing an indication as to the amount of kerosene which will prove effect- 

 ive for a given surface of water, and also as affording some indication 

 of tlie length of time for Avhich a single application will be operative. 

 It is true that upon this last point the observations were not complete, 

 owing to my departure after ten days, but as already indicated, the in- 

 fluence of the kerosene outlasted all ocular or odorous evidence of its 

 presence, and there is every reason to suppose that it would have con- 

 tinued for at least some days longer. 



As a general thing, in larger ponds, which are of a more permanent 

 character, the presence of fish is a check upon the multiplication of the 

 mosquito. These insects breed mainly in marshy lands, where small 

 pools, surrounded by wet soil, adjoin each other, and such spots, where 

 accessible, can be readily aud economically treated with coal oil. The 

 economy of the operation is shown by a simple estimate from the data 

 which I have given, that 5 gallons of coal oil, costing say GO cents, will 

 treat 9,600 square feet of water surface, or, to carry the computation 

 still further, a barrel of kerosene, costing $4.50 will treat 96,000 square 

 feet of water surface. 



With this remedy and with the drainage of swamp lands where prac- 

 ticable, with the introduction of fish into i)onds in which they do not 

 already occur, and with the careful watching of rain-water barrels 

 and tanks, the mosquito plague in many localities can be readily and 

 greatly lessened. Where mosquitoes breed, however, in the long suc- 

 cession of brackish marshes on the seacoast, remedial work is practically 

 hopeless. I anticipate not the slightest practical outcome from Mr. 

 Robert H, Lamboru's dragon-fly proposition, and believe that relief in 

 4388— No. 1 2 



