TOXICITY OF SPINOSAD TO SUSCEPTIBLE AND RESISTANT STRAINS OF HOUSE-FLIES, MUSCA-DOMESTICA

The toxicity of spinosad, a new insecticide derived from the bacterium Saccharopolyspora spinosa, was evaluated against susceptible and resi stant strains of house fly (Musca domestica L.). Spinosad was highly t oxic to house flies based on 72-h LD50 values and the symptoms of pois oning were consistent with a neurotoxic mechanism of action. Spinosad was relatively slow acting, with the maximum toxicity noted at 72 h. P iperonyl butoxide and S,S,S,-tributylphosphorotrithioate synergized th e toxicity of spinosad by 3.0- and 1.8-fold, respectively, while dieth yl maleate had no significant effect. These results suggest that there is a small degree of monooxygenase-mediated spinosad detoxification i n house flies, while hydrolases may be only minimally important and gl utathione transferases may have no role. There were no substantial lev els of cross-resistance detected, except in the LPR strain where a low 4.3-fold cross-resistance was observed. The cyclodiene-resistant OCR strain was 2.7-fold more sensitive to spinosad than the susceptible st rain (CS). These results suggest that cross-resistance may not be a li miting factor for the use of spinosad against house flies. (C) 1998 So ciety of Chemical Industry