Abstract
LD50 values of some pyrethroids in the housefly, Musca domestica L. (Lab-em-7-em strain) were obtained by means of a quantitative oral application method. Oral LD50 values of all the pyrethroids tested-phenothrin, cyphenothrin, permethrin, cypermethrin, cyfluthrin, deltamethrin and fenvalerate, were 5-10 times as large as topical LD50 values. Piperonyl butoxide and S, S, S-tributylphosphorotrithioate induced higher synergistic effects in the oral application than in the topical application. As a result, the differences of the LD50 values between oral and topical applications were smaller, though the oral toxicities did not exceed the topical toxicities. This suggested that pyrethroids applied orally could be more vulnerable to degradation by mixed function oxidase and esterase.
