178 The Control of Mosquitoes 



many Anopheles breed in brackish water and 

 Culex breed in salt-water marshes and pools. 

 This defect, however, is shared by all the com- 

 mercial larvacides tested on the Isthmus. 



2. The ptore larvacide deteriorates upon expo- 

 sure to the air and must be kept in drums, barrels, 

 and other tightly closed containers. 



3. It rapidly loses its toxicity after mixing 

 with water containing algae and other organic 

 matter. After twenty-four hours its toxicity is 

 so far diminished that it is practically non-toxic 

 from the standpoint of field practice. 



The ideal mosquito lavacide should, in addition 

 to possessing all the desirable qualities of the 

 phenol-resin soap described above, possess none 

 of the disadvantages enumerated. We have not 

 yet fotmd such a product, either on the market or 

 by experimenting with various mixtures. 



The toxic action of the pheno-resin larvacide 

 upon mosquito larvae is probably due to the action 

 of its phenol content upon the protoplasm of the 

 larvae, probably intensified by the fact that the 

 phenol is in emulsion. 



We have had practical field experience with 

 Pyrocresol. In composition and action this pro- 

 duct closely resembled the pheno-resin larvacide 



