386 MOSQUITOES or noeth ameeica 



half an hour, and 1 part to 5000 parts of water will Idll anopheles larvaB in from 

 five to ten minutes, or less. This property of killing larvae rapidly is of great 

 importance in the Tropics, where continuous rainy periods make crude oil or 

 kerosene much less valuable as a larvacide than it is in northern latitudes having 

 less rainfall. Also the larvacide acts as an algecide, and thus destroys the food 

 and the hiding places of anopheles larvae. As it takes up very little room, com- 

 pared with the area it can be spread over, the cost of distribution will be much 

 less than that of crude oil or kerosene — considering the large territory which 

 the antimalarial work covers, this item alone is of great financial advantage to 

 the department. 



" Tests have recently been made to determine approximately how much of the 

 new larvacide will be needed per month (rainy season) for each district. 



" Although this larvacide will be used to a large extent, yet we shall con- 

 tinue to use crude oil for streams having a fair velocity, as such application gives 

 excellent results and is as economical as larvacide would be, as the oil is spread 

 in a very fine film automatically. In order to make the crude oil drip with con- 

 tinuous regularity, a piece of metal similar to that part of a flat-wick lamp 

 which holds the flat wick is fastened to the oil container. It is made somewhat 

 larger than the wick, so that the wick flts it loosely when saturated with the 

 grade of fuel oil we use. This metal wick chamber is fitted to the oil container 

 about 3 inches from its base. The space below the wick chamber is filled with 

 a solution of caustic soda or of larvacide. As the oil is attracted along the wick 

 by capillary attraction, it comes into contact with the larvacide or caustic soda 

 and is ' cut,' rendered thinner. This method of procedure prevents the wick 

 from being clogged by the thick fuel oil and enables the wick to drip the oil 

 desired." 



In the September, 1909, report, it is stated that the new larvicide was giving 

 very satisfactory results and would undoubtedly reduce the cost of anti-malarial 

 work, besides being more effective than crude oil in many places. It also has 

 some value as a destroyer of vegetation, thus making conditions less favorable 

 to mosquito breeding. In the October report satisfaction with its use is again 

 expressed, and it is stated that the fact that it kills the grass at the edges of the 

 ditches will be of importance in reducing the cost of anti-malarial work. 



Mr. August Busck, of the Bureau of Entomology, U. S. Department of Agri- 

 culture, has recently had an opportunity to witness the effectiveness of this 

 preparation and has furnished us the following account of its effects and manner 

 of application : 



" Friday I had a very excellent opportunity to observe the application and 

 result in the field, in one of the outlying districts, near Rio Grande on the 

 Isthmian Canal Zone. Here was about a mile and a half of a small slow-run- 

 ning stream, passing through a scattered native village and through thick brush, 

 which for some reason had been overlooked or neglected. This was literally 

 swarming with Anopheles larvae and pupae everywhere along the grassy edges 

 and in the small pools caused by the native washerwomen, or by pigs, poultry 

 and horses. It was about as nasty a place as I have seen, producing thousands 

 of adults every day. 



" The local sanitary inspector, Mr. Trask — one of the most efficient — kindly 

 postponed action until I had been over the ground thoroughly, and then started 

 a man with a knapsack-pump, another with larvicide supply for the pump and a 

 foreman to oversee the job, from the head spring down along the stream ; they 

 walked right along and sprayed with a 1 to 6 solution as they went, covering 



