The Mosquitoes of New Jersey 179 



Nitre cake, which is a by-product of gun-cotton manufacture and 

 available in large quantities at a low price was given a pretty thor- 

 ough trial. So much has been said about this substance as a larvi- 

 cide that a presentation of certain experiments seems worth while. 



Experiments i, 2 and 3 are designed to determine the minimum 

 dosage for the house mosquito, which was selected as a type of the 

 fresh-water forms. 



Experiment 1 



OBJECT. To determine the minimum dosage of nitre cake for Culex 

 pipiens a series of jars, each containing about r,ooo cc. of water, was set 

 up as follows : 



2 gm. of nitre cake in 1,000 cc. of tap-water. 



4 gm, of nitre cake in 1,000 cc. of tap-water. 



6 gm. of nitre cake in 1,000 cc. of tap-water. 



8 gm. of nitre cake in 1,000 cc. of tap-water. 

 10 gm. of nitre cake in 1,000 cc. of tap- water. 

 No nitre cake in 1,000 cc. of tap-water. 



Twenty-five larvae of Culex pipiens were placed in each of the above jars 

 at 12:15 p. m., July 19, 1917. At 8:30 a. m., July 20, 1917, all larvae in the 

 treated jars were dead, while all larvae in the check jar were alive. 



Experiment 2 



OBJECT. To determine the minimum dosage of nitre cake for Culex 

 pipiens. Solutions of nitre cake in tap-water were made up as follows : 



50 gm. of nitre cake in 1,000 cc. of tap-water. 

 25 gm. of nitre cake in 1,000 cc. of tap-water. 

 10 gm. of nitre cake in 1,000 cc. of tap-water. 

 I gm. of nitre cake in 1,000 cc. of tap-water. 

 No nitre cake in 1,000 cc. of tap-water. 



The temperature was 72°. Fifteen larvae of Culex pipiens were placed in 

 each jar at 3:30 p. m., July 13, 1917. At 5:15 p. m. the jars were observed 

 with the following results : 



All larvae dead in the 25 and SO-gm. solutions. 



Five of the younger larvae (second molt) in the lo-gm. solution dead, 

 all others alive. 



All alive in the i-gm. solution and the check. 



At 8:30 a. m., July 14, 1917, the larvae dead in all jars except the check. 



