INSECTICIDES AND REPELLENTS 89 



PHOSPHORUS INSECTICIDES 

 Parathion 



Owing to its high toxicity to mammals, the use of parathion for 

 controlling insects affecting man is not advocated. 



The acute median lethal oral dose of parathion for laboratory 

 animals is about 3 mg. per kilogram of body weight, which is much 

 lower than that of any of the chlorinated hydrocarbon insecticides. 

 When it is applied to the skin, the acute median lethal dose is about 

 40 to 50 mg. per kilogram of body weight. Calves are poisoned 

 when sprayed with a concentration as low as 0.025 percent. 



EPN 



EPN, like parathion, is highly toxic to mammals. 



The acute median lethal oral dose for laboratory animals is about 

 14 mg. per kilogram of body weight, which represents about one- 

 fourth the oral toxicity of parathion. The acute dermal toxicity is 

 about the same as that of parathion. Although it is highly toxic 

 to calves, these animals appear to be less susceptible to EPN sprays 

 than parathion, the concentration causing death being about 2 to 4 

 times higher. 



TEPP 



TEPP is of little interest in medical entomology because of its 

 high toxicity to animals and its short residual effectiveness, but it is 

 used in baits for fly control. 



The acute median lethal dose for laboratory animals is about 1.2 

 mg. per kilogram of body weight when given orally and about 5 mg. 

 per kilogram when applied to the skin. 



Malathion 



Malathion is much less toxic to man and animals than the other 

 phosphorus insecticides. Its acute oral toxicity to laboratory animals 

 is less than that of DDT. The chronic oral toxic effects are also low. 



The dermal toxicity to calves is about the same or slightly higher 

 than that of toxaphene and chlordane. Sprays containing 1 percent 

 caused fatalities. Concentrations of 0.5 and 0.25 percent produced 

 no gross symptoms of toxicity. 



Diazinon, Bayer L 13/59, and Chlorthion 



Such toxicity data as are available at present indicate that Diazinon 

 is about as toxic to warm-blooded animals as TEPP; Bayer L 13/59 

 and Chlorthion are much less toxic, perhaps even less so than mala- 

 thion. 



Special Precautions in Using Phosphorus Insecticides 



The phosphorus insecticides previously discussed, as well as Systox 

 (active ingredient demeton), schradan, methyl parathion, para-oxon, 

 HETP, and similar insecticidal materials in common agricultural usage, are 

 all cholinesterase inhibitors, and sublethal exposure to any one o£ them 

 may increase the toxic effects of any other. Avoid continued exposure 

 to any phosphorus insecticide. 



