120 N. J. Mosquito Extermination Association 



practice, the perfect film cannot always be obtained. Especially 

 is this true in salt marsh and fresh water swamp control, where con- 

 tinuity of the oil film is impossible, owing to the presence of cat- 

 tails and other grasses, normally present. The perfect film is 

 prevented by wind action, floatage, vegetation and sewage or other 

 organic matter and is easily destroyed by medium or heavy rains. 

 The intelligence and the interest in the work of the oiling squads 

 and the intelligent supervision of their work, has a direct bearing 

 on the effectiveness of petroleum. 



Larvicides : 



Larvicides or substitutes for petroleum are certain substances 

 that will diffuse with water uniformly and with fair rapidity, kill- 

 ing mosquito larvae when they come in contact with it. 



The Panama Larvicide, described by Le Prince and Orenstein, 

 in their book **Mosquito Control in Panama" consists of crude car- 

 bolic acid, resin and caustic soda. In addition to being a larvicide, 

 this is useful in destroying algae, and is a good disinfectant. As a 

 mosquito larvicide it is used by spraying an aqueous emulsion (one 

 part larvicide to five parts water) over the surface to be treated 

 and along the margins of pools and ponds, or other mosquito breed- 

 ing places. This larvicide kills in a dilution from i :iooo to i : 15000. 



The advantages of this larvicide, as set forth by Le Prince and 

 Orenstein are : 



a — High toxicity to mosquito larvae. A 1 15000 emulsion kills full grown 



larvae in from 3 to 19 minutes. 

 2. — Concentration. Being effective for practical use in a 1 15000 emulsion only 



a relatively small amount of the larvicide need be transported to a given 



body of water. 



3 — Uniformity of toxic power. This product, when carefully made, is uniform 



in toxicity. 



4 — Simplicity of composition. The manufacture of this larvicide requires 



neither complicated apparatus nor highly skilled labor. 



5 — Low toxicity to higher animals. It is practically harmless in ordinary 



dosage or in dilution to cattle, poultry, etc. 



6— Rapidity of toxic action. When used in the field, it killed all anopheles 



larvae and pupae in 10 to 20 minutes. 



7 — Cheapness of the product. In Panama, the cost is about eighteen cents a 



gallon. 



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 larvicide 



