184 N. J. Agricultural Experiment Station, Bulletin 348 



8. Absence of danger from fire. The concentrated larvicide is inflammable, 

 but not easily ignited. In dilution it is not inflammable. 



9. It is useful in the rapid determination of the presence of mosquito 

 larvae and kills those at rest embedded in the mud. 



10. In addition to its toxicity for mosquito larvae the phenol-resin larvi- 

 cide is also highly toxic to protozoa and algae, as well as most of the varieties 

 of the common grasses encountered in Panama. 'The algacidal and herbicidal 

 properties of this larvicide are of frequent use in mosquito eradication. 



disadvantages 



The disadvantages of this larvicide are : 



1. It does not emulsify and is inert in brackish zvater. This is a serious 

 disadvantage because many Anopheles breed in brackish water and Culex 

 breed in salt-water marshes and pools. This defect, however, is shared by all 

 the commercial larvicides tested on the Isthmus. 



2. The pure larvicide deteriorates upon exposure 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 24 hours its toxicity is so far diminished 

 that it is practically non-toxic from the standpoint of field practice. 



The ideal mosquito larvicide 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 found such a product, 

 either on the market or by experimenting with various mixtures. 



The toxic action of the phenol-resin larvicide 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. 



Conclusions 



The preceding account of larvicides does not pretend to recount 

 the really immense number of substances that have been tried but 

 merely to bring out the experience of certain organizations that have 

 been engaged in practical mosquito control on a large scale. It thus 

 appears (so far as the writer's knowledge goes, experimental and 

 practical work elsewhere but not reported in this bulletin seems to 

 be in substantial agreement) that no larvicide has yet been devised 

 which covers as wide a field or is as practical under all conditions 

 as is petroleum oil. It is not for a moment denied that certain 

 larvicides may not fit specific cases better than oil but it is maintained 

 that they take a place in mosquito control as adjuncts and supple- 

 ments to petroleum oil as larvae killers. 



The best petroleum oil is one which readily forms a complete 

 homogenous film when applied to the water surface by a small port- 

 able sprayer, and one which remains eflfective for at least two weeks, 

 or better still for one month. In the experiments above recorded it 



