174 N. J. Agricultural Experiment Station, Bulletin 348 



is especially important, because most of the important species come to 

 the surface for air. Normally small fish are better mosquito exter- 

 minators than large ones. Gold-fish may be used where they are pre- 

 ferred to other species. 



Larvicides 



This term is usually applied to some substances destructive to mo- 

 squito wrigglers, which will mix with the water. A large number 

 of these substances have been tried, as set forth in the following 

 summary, but the ideal is yet to be found. Such an ideal larvicide 

 should destroy quickly all mosquito larvae with which it comes in 

 contact, should be non-poisonous to man and the higher animals, 

 should be non-injurious to water plants, should remain efifective in 

 the pool throughout the season even when it becomes dry and refills 

 many times, and should be cheap enough to render its use prac- 

 ticable under ordinary mosquito-control conditions. 



Sodium Chloride and Calcium Chloride (NaCl and CaCla). 

 The work on these substances confirmed the results obtained by 

 Chidester^^ and showed that the amount necessary (of NaCl and 

 CaClg) was such as to render the use of either impracticable from 

 the standpoint of cost. 



Sodium Hydroxide (NaOH). The resistance of fully-grown 

 larvae of A. cantator and A. sollicitans to NaOH was determined by 

 adding it to creek-water (2.9 per cent salinity) in doses ranging from 

 o.oooi gm. to 0.2 gm. per 1,000 cc. Two-tenths of a gram had 

 killed everything in 3 days. Another test, in the course of which 

 tap-water was substituted for creek-water, was then set up with 

 amounts of NaOH ranging from 0.5 gm. per 1,000 cc. In two days 

 some killing was visible in the i-gm. solution, more in the 5-gm., 

 and complete killing in the 20-gm. A brown precipitate appeared 

 in all jars from o.i gm. up. 



Sodium sulfo-carhonate. (A commercial article, not C. P. It 

 was prepared by the Dow Chemical Company. ) This compound was 

 used in testing the resistance of fully grown larvae of A. cantator 

 and A. sollicitans in tap-water to a strength ranging from i to 3 

 cc. of the material to 100 cc. of water. In two days the larvae 

 had transformed to pupae and some adults had emerged. 



"Chidester, F. E. 1916. The influence of salinity on the development of 

 certain species of mosquito larvae and its bearing on the problem of the dis- 

 tribution of species. N. J. Agr. Exp. Sta., Bui. 299. 



