Abstract
The synergistic toxicity data of allethrin, fenvalerate, tetramethrin, permethrin or phenothrin with piperonyl butoxide to the house fly, Musca domestica, was analyzed by fitting a mathematical model proposed by HEWLETT (1969), y=a+b1 logz1+b2z2/(c+z2), where y is probit mortality, z1=dose of pyrethroid, z2=dose of piperonyl butoxide; a, b1, b2 and c are parameters. The parameters were estimated in two ways, viz. the graphical procedure described by HEWLETT and the probit plane analysis shown by FINNEY (1952). The model was fairly applicable to the data, and the mixtures with an indefinitely large ratio of piperonyl butoxide were estimated to be 21.10, 11.52, 9.70, 6.74 and 5.73 times as toxic as allethrin, fenvalerate, tetramethrin, permethrin and phenothrin alone, respectively.
