40 CIRCULAR 9 7 7. U. S. DEPARTMENT OF AGRICULTURE 



The solutions used in fog machines usually consist of 5 percent 

 of DDT in fuel or diesel oil, or up to 10 percent in a mixture of fuel 

 oil and an aromatic petroleum fraction (such as Velsicol AR-50 and 

 S/Y Sovacide 544-B), or other auxiliary solvent. In experimental 

 work in Alaska with Tifa and Dyna-Fog generators and a modified 

 jeep exhaust generator, the 20-percent DDT airplane spray caused 

 excessive carbonization. When the 20-percent solution was reduced 

 to 10 percent with fuel oil. it worked satisfactorily and produced a 

 dense fog. The output of Tifa and Dvna-Fog generators ranges 

 from about 20 to 40 gallons per hour. The Tifa has been reported to 

 disperse as much as 60 gallons per hour. 



The exhaust generator used in Alaska had an output of only about 4 

 gallons per hour, which was too low to give the desired dosage at a 

 reasonable speed. A model developed in California was reported to 

 give 10 gallons per hour when a %-inch venturi was employed. 

 Even at this rate and with a 10-percent solution, the vehicle speed 

 must be held to 2 m. p. h. to give an output of 5 gallons per mile, 

 which is equivalent to about 0.055 pound of DDT per acre assuming 

 a swath width of 600 feet. 



The use of exhaust generators may damage motors from the back 

 pressure created by the constriction in the venturi and from operation 

 of the vehicle in low gear at high speeds to give effective discharge 

 rates. 



Outdoor Residual Treatments 



Most species of mosquitoes rest outdoors in vegetation and may or 

 may not enter buildings for blood meals. Experiments were carried 

 out to determine the effect on the mosquito population of residual 

 applications of DDT sprays to low vegetation and ground litter. 



In early tests against Aedes taeniorhynchus in heavy vegetation 

 3 to 5 gallons per acre of an oil or emulsion spray containing 5 percent 

 of DDT greatly reduced the population for several weeks. During 

 the first 2 weeks the reduction ranged from about 80 to over 95 

 percent. 



In later tests DDT. chlordane, BHC, and dieldrin were compared 

 in residual sprays on 2-acre plots surrounding small isolated dwellings 

 in coastal areas. The insecticides were applied with a small power 

 sprayer at the rate of 50 gallons of emulsion containing from % to 2 

 pounds of active ingredient per acre. Lindane and BHC containing 

 40 percent of gamma were the most effective materials, both causing 

 a great reduction for 17 days at all dosages. Dieldrin was effective 

 for 13 days at the 2-pound dosage but for only 3 to 7 days at the 

 lower dosages. With DDT and chlordane the reduction dropped 

 below 90 percent after the third day at the highest dosage. Resist- 

 ance may have been a factor in the short residual protection obtained 

 with DDT. In the Northwest against snow-water species such 

 treatments provided excellent daylight protection for 3 to 4 weeks. 

 The reduction of mosquito annoyance about the houses by such 

 residual treatments was marked during the daytime but much less so 

 at night. 



This method of protecting campsites and bivouac areas should 

 prove practicable in certain situations, and the treatments can be 

 repeated as often as required. In heavy vegetation single applica- 



