Mechanism of Action of Certain Synergists for DDT against Resistant House Flies

Certain compounds structurally related to DDT, [2,2-bis (p-chlorophenyl)-1,1,1-trichloroethane], may act as synergists for DDT against insecticide resistant house flies (Summerford et al., 1951 March et al. 1952). Three obvious questions come to mind with respect to these findings. First, how do these synergists exert their effect; second, b y what mechanism can the house fly eventually become resistant to the combination (March el al. 1952); and third, why do these synergists potentiate the toxicity of DDT for resistant flies but not for susceptible flies? The answer to these questions would have an important bearing upon the significance of the fact that DDT resistant flies rapidly dehydrochlorinate DDT (Sternburg et al. 1950, March & Metcalf 1950, Winteringham et al. 1951). Perry et al. (1953) propose that the synergist DMC, [bis (p-chloropbenyl) methylcarbinol], acts by interfering with the mechanism which detoxifies DDT. Since these experiments were necessarily carried out by in vivo procedures, their proposal might be questioned as to whether this is actually the cause or merely the result of synergism.