12 CIRCULAR 9 7 7, TJ. S. DEPARTMENT OF AGRICULTURE 



compounds have also shown a less marked synergistic effect with 

 allethrin. 



OTHER INSECTICIDES 



The materials described previously are the principal insecticides em- 

 ployed in the control of insects of medical importance. Others 

 are used occasionally or for special purposes. 



Toxaphene is a chlorinated camphene containing 67 to 69 percent 

 of chlorine. It is an effective mosquito larvicide and has been used 

 against DDT-resistant mosquitoes. It is of value for controlling 

 chiggers and ticks. Toxaphene is also effective against the body 

 louse, but its safety to man when used for this purpose has not been 

 established. 



Parathion and EPA 7 , two organic phosphorus compounds, are toxic 

 to many insects but also to warm-blooded animals, and have not 

 been approved for use in controlling household insects. In one 

 South American country, however, parathion has been used, under 

 careful supervision, in a residual spray in houses for controlling 

 DDT-resistant house flies. It is used extensively in the United States 

 for the control of pests on field crops and fruits. EPX is less toxic 

 than parathion to warm-blooded animals and is being considered 

 for use in the control of mosquito larvae resistant to the chlorinated 

 hydrocarbons. 



Parathion is a yellowish liquid with a characteristic odor. Its 

 specific gravity is 1.26 and its boiling point is 191° C. or higher at 

 760 mm. The technical grade has a minimum purity of 95 percent 

 and is often deep brown in color. Its chemical name is 0,0-diethyl 

 O-^-nitrophenvl phosphorothioate, and its molecular formula 



c 10 h 14 no 5 ps; 



EPN is a pale-yellow crystalline solid having a melting point of 

 30° C. The technical material is an amber-colored liquid with a 

 specific gravity of 1.27 at 25°. It is soluble in most organic solvents 

 but practically insoluble in water. Its chemical name is O-ethyl 

 (9-^-nitrophenvl phenvlphosphonothioate, and its molecular formula 

 C 14 H 14 N0 4 PS; 



A number of other organic phosphorus compounds have been 

 synthesized and are being evaluated as insecticides. They include 

 methyl parathion. malathion, para-oxon, TEPP, Diazinon (0,0-diethyl 

 0- (2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate) , Bayer 

 L 13/59 (0,0-dimethyl 2,2,2-tricliloro-l-hydroxyethylphosphonate), 

 and Chlorthion (0-(3-chloro-4-nitrophenyl) 0,0-dimethyl phosphoro- 

 thioate). Some of them are less toxic than parathion and EPX to 

 mammals and may prove more suitable for use in the field of medical 

 entomology. 



INSECTICIDE FORMULATIONS 



Solutions 



In the discussion of insecticide formulations the concentration of 

 solutions is usually given on a weight -per- volume (w/v) basis, but 

 some of the military and Federal specifications are given on a weight - 

 per-weight (w/w) basis. Because the volume of liquids changes with 

 the temperature, it is necessary to state the temperature at which 

 the weight-volume solution is prepared. A temperature commonly 



