Insecticidal activities of Dowco-214,O, O-dimethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate, against the German cockroach, Blattella germanica L., the American cockroach, Periplaneta americana L., and the smoky brown cockroach, Periplaneta fuliginosa L., were evaluated under a laboratory condition of 25±1℃ and 60±5% R.H. The (LD)_<50>'s for male adults of the German cockroach determined by topical application decreased in order of dichlorvos, Dowco-214,fenitrothion, Dursban, fenthion, diazinon, dieldrin and malathion. At the level of (LD)_<90>, Dowco-214 was most effective. For male adults of the American cockroach, the (LD)_<50>'s decreased in order of dichlorvos, Dursban, Dowco-214,fenitrothion, diazinon and fenthion. In the test using male adults of the smoky brown cockroach, Dursban was most effective and the (LD)_<50>'s decreased in order of fenitrothion, diazinon and Dowco-214. However, the differences of toxicities between Dowco-214,fenthion and fenitrothion were not significant. Residual effectiveness of Dowco-214 on plywood panel tested by the limited time contact method was longer than that of several insecticides. In the test by the succesive time contact method, effective persistence of Dowco-214 on plywood panel was longer than that of Dursban and diazinon. It is presumed that Dowco-214 is one of the most promising insecticides for controlling insects of public health importance because of its higher insecticidal activity, longer residual effectiveness and lower toxicity to mammals.
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