i82 N. J. Agricultural Experiment Station, Bulletin 348 



Experiment 6 was undertaken to determine the persistence of nitre 

 cake in fresh water. It was not thought advisable to make a similar 

 test in salt water because the salt pools are always subject to dis- 

 turbance by the tide. 



Experiment 6 



OBJECT. To determine the persistence of nitre cake as a larvicide. 



A large wooden tub containing a layer of mud and approximately 40 liters 

 of water in which larvae of Culex pipiens were present was treated with 400 

 gm. of nitre cake, at 12:30 p. m., July 19, 1917. A check tub of the same 

 dimensions with the same contents was left untreated. Examinations were 

 made 30 hours later. All larvae in the treated tub were dead and none 

 of those in the untreated tub were dead. Some of the pupae were destroyed 

 in the treated tub and some had given up adults. 



On Friday, August 3, 1917, a number of Culcx pipiens larvae were placed 

 in the treated tub. Twenty-four hours later all these larvae were dead. No 

 oviposition took place in the water of the treated tub from the time of treat- 

 ment, July 19 to August 9, 1917. It thus appears that I gm. of nitre cake to 

 1,000 cc. of water is barely sufficient to destroy the larvae of Culex pipiens in 

 2 days' time, but that stronger solutions (i gm. of nitre cake to 100 cc. of 

 water) destroy the species readily and remain effective for 21 days or longer 

 It thus appears that 6 gm. of nitre cake to 1,000 cc. of water testing 7 per cent 

 salinity is necessary to destroy the larvae of Aedes sollicitans and that 3 

 days are required to accomplish this result. 



The bearing of these results upon the practical use of nitre cake 

 as a larvicide needs elucidation. In view of the fact that a diminu- 

 tion in the strength of the solution results in loss of efficiency, nitre 

 cake should not be used as a larvicide except in pools and bodies of 

 water that have no outlet. In view of the cost of distributing the 

 material, it would seem unwise to use the minimum strength. Enough 

 should be put in to insure not only prompt destruction of the larvae 

 but a reasonable continuance of that effect. Considerable time is 

 required for dissolving the nitre cake, and its distribution through 

 the water is relatively slow. Throwing the material into the pool 

 in a cake or even in ground form is likely to result in unsatisfactory 

 results because of the slowness with which the material will dissolve 

 and the slowness with which the dissolved material will distribute. 

 These difficulties are great and need to be overcome before its use 

 will be practical. 



Canal Zone Larvicide 



COMPOSITION 



In the course of their work in Panama, Le Prince and Orenstein^^ 

 developed a larvicide, the active principal of which was carbolic 



"Le Prince, J. A., and Orienstein, A. J., 1916, Mosquito Control in Panama. 



