16 CIRCULAR 97 7, U. S. DEPARTMENT OF AGRICULTURE 



settling, and they would be of special value as mosquito larvicides. 

 However, a satisfactory formulation for practical use has not yet been 

 produced. 



Dusts and Dusting Powders 



DDT dusts have been used widely for louse control and also to 

 some extent against other insects of military importance, such as 

 mosquito larvae, cockroaches, ticks, and chiggers. In civilian health 

 programs their greatest use at present is for the control of rat fleas 

 in the natural habitats of then* hosts. For all these uses 5- or 10- 

 percent dusts are usually employed. 



Technical DDT, because of its low melting point, is difficult to 

 grind alone to produce a powder sufficiently fine for direct mixing 

 with a diluent. However, it can be ground with a diluent such as 

 pyrophyllite or talc, or the diluent can be impregnated or blended 

 with a solution of DDT in a volatile solvent. By these means dusts 

 containing 25 to 75 percent of DDT can be produced and reduced to 

 the desired concentration by mechanical mixing. The wet table 

 powder can also be diluted in a similar manner and applied as a dust. 



The principal military use for DDT powders is in the control of 

 lice by application to the clothing or hair. Specifications have been 

 issued for two powders, one containing 10 percent in pyrophyllite 

 (No. 5) and the other containing in addition 0.2 percent of pyrethrms 

 and 1 percent of piperonyl butoxide (No. 4). After the discovery of 

 DDT-resistant lice in Korea and Japan, a 1-percent lindane powder 

 was developed (No. 3). These materials are also intended for limited 

 use by individuals against fleas, bed bugs, and other crawling insects. 



Another specification (No. 6) provides for pyrethrum powders for 

 louse and flea control. One powder contains 0.2 percent of pj^ethrins 

 and 2 percent of the synergist sulfoxide together with an ovicide, an 

 antioxidant, and a powder conditioner. Another powder contains in 

 addition 0.3 percent of allethrin. The louse powders are packaged 

 in 2-ounce containers for individual use and larger containers for 

 mass dusting. 



Granulated Insecticides 



Granulated insecticides have been developed to enable more efficient 

 treatment of mosquito and sand fly breeding places protected by dense 

 vegetative cover. Granular bentonite and attapulgite of 16/30 and 

 30/60 mesh have been used in tests. Little or none of the granular 

 material is lost through adherence to the foliage, whereas the loss is 

 usually high with sprays and dusts. Granulated insecticides may 

 also be applied satisfactorily under weather conditions that would 

 preclude the use of sprays or dusts. 



In experimental studies some of the materials were prepared in a 

 concrete mixer by spraying a solution of the insecticide in benzene 

 onto the carrier while the mixer was rotating. Granulated BHC was 

 also prepared by spraying the carrier with melted BHC of 36-percent 

 gamma content, which eliminated the need of a solvent with this low- 

 melting material. Concentrations ranging from 2.5 to 8 percent were 

 prepared for different purposes. 



Liquefied-Gas Aerosols 



The high-pressure pyrethrum aerosol was devised by L. D. Goodhue 



