122 N. J. Mosquito Extermination Association 



Nitre cake is fairly efficient, but its use is somewhat limited, 

 being entirely unsuited to running streams or to ponds frequently 

 washed out by heavy rains. Its use is practical, however, in treat- 

 ing fire barrels, vats, old wells, abandoned cisterns, or any arti- 

 ficial container, where there is no danger of poisoning persons or 

 stock. 



The advantages of nitre cake as a larvicide are : low cost, in carload lots 

 averaging fifty tons to the car ; nitre cake costs about $5.00 per ton ; remains 

 effective for a month or more ; readily kills larvae in a dilution of i :400. 



The disadvantages of nitre cake are: destructive to the skin and clothing; 

 poisonous to stock; diffusion relatively slow; alkalinity of soil neutralizes 

 active agent, namely, sulphuric acid ; limited use. 



Water gas tar is a by-product of the manufacture of illuminat- 

 ing gas. It has been used by several workers and found to be 

 very effective. This by-product has practically the same gravity 

 as water, having a tendency to float in masses slightly below the 

 surface of the water. Owing to chemical properties of the tar 

 (phenol, naptha and creosote oils) larvae are killed in much less 

 time than is required with a film of oil. I have noticed larvae of 

 Culex pipiens become inactive a short time after coming in contact 

 with a mass of the tar. Water gas tar can be used straight or 

 mixed with kerosene and fuel oil, greatly increasing their effici- 

 ency and resistence to conditions that tend to break the film. This 

 product can usually be obtained free of charge or at a nominal 

 cost at any plant manufacturing gas by the water gas process. Its 

 use is recommended as an efficient and practical, as well as an 

 economical control measure. 



Many tests have been made during the past few years to determine 

 the value of creosote as a larvicide. Metz, who has experimented 

 with creosote states : 



"Cresote may prove to have some advantages due to the fact that it is 

 more lethal than kerosene and that it may be effective without forming a 

 complete film. In addition to its direct action on the larvae, it is effective 

 in reducing the larval food supply. The principal features of this method of 

 control as revealed by the preliminary tests, are as follows : Refined or com- 

 mercial cresote, of a dark color and a consistency slightly thicker than kero- 

 sene, is applied in the form of a fine mist spray. The application differs 

 essentially from that of kerosene or crude oil in that the cresote oil is broken 

 up into minute particles that float in the air like mist. Thus, only a small 

 amount of this material is used, as compared with the ordinary method of 

 oiling. The style pump used in the tests was of the automatic type that re- 

 tains compression, so as to provide a constant mist. Such a mist will settle 



