INSECTICIDES AND REPELLENTS 29 



Two hand-operated dusters (fig. 3) are available as military-issue 

 items. One is of the plunger type (No. 6, table 4) and the other, a 

 larger one, called a rotary duster (No. 4), has a fan and a shoulder 

 strap. In water shallow enough for wading the dust can be dispersed 

 in swaths. When the water is deeper, the dusting may be done from 

 the upwind shore or from a boat. With a light, favorable breeze a 

 wide swath can be covered. 



Other Larvicides 



Several chlorinated hydrocarbons other than DDT, including 

 chlordane, benzene hexachloride, lindane, dieldrin, and heptachlor 

 (see pp. 6-10), are highly toxic to mosquito larvae, and specifications 

 for most of them have been prepared covering formulations for 

 certain types of insect control for use by the Armed Forces. Several 

 of the organic phosphorus compounds are also effective larvicides. 



In laboratory tests EPN and parathion, followed by dieldrin, were 

 the most toxic to the larvae of several species. In field tests EPN, 

 parathion, dieldrin, and lindane have generally been the most effective. 



Table 5 gives the approximate lethal dosages of various larvicides 

 against the common malaria mosquito, the yellow-fever mosquito, 

 the southern house mosquito, the salt-marsh mosquitoes, and mixed 

 populations of subarctic Aedes. 



In the laboratory tests acetone-water suspensions were used under 

 fairly uniform conditions. The field tests were run on small measured 

 plots with either oil solutions or emulsions. 



In some tests the highest dosages gave a kill of less than 95 percent, 

 and the minimum lethal dosage was estimated from the kill obtained. 

 Even in the laboratory the results varied greatly with different lots of 

 larvae. In eight tests with DDT, for example, the minimum lethal 

 dosages against the malaria mosquito ranged from 0.0025 to 0.01 

 p. p.m. 



Since some of the figures in the table are based on only one or two 

 tests the data are not strictly comparable and may be slightly mis- 

 leading as to relative effectiveness. The records do show, however, 

 that all the compounds in this group are highly toxic to more than one 

 species of mosquitoes and any of them may be worth considering for 

 use in specific problems. Important factors that must be considered 

 are the hazards of the chemicals to the operators, effects on fish and 

 wildlife, and relative cost against different species. 



In the coastal areas in Florida where resistance to DDT was found 

 among salt-marsh mosquitoes, most of the larvicides in table 5 were 

 tested with a view to selecting satisfactory substitutes. Lindane, 

 dieldrin, heptachlor, and EPN gave favorable results in both labora- 

 tory and field tests. Chlordane had a low minimum lethal dosage in 

 laboratory tests but was less effective in field tests. Aldrin showed 

 a high order of toxicity in some field tests and should be tested further. 

 Parathion and EPN were the most toxic materials tested in the 

 laboratory, but in several field tests parathion showed the same toxicity 

 as toxaphene. In other series parathion was as effective as EPN 

 and malathion. 



