Quantitative aspects of the synergism between carbaryl and some 1,3‐benzodioxole (methylenedioxyphenyl) compounds in houseflies

Abstract

The synergism of carbaryl (1‐naphthyl‐N‐methyl carbamate) with 26 derivatives of 1,3‐benzodioxole and naphtho‐1,3‐dioxole was examined by topical dosage of female houseflies, Musca domestica, which, though of a strain not selected with insecticides, were completely tolerant to carbaryl. The synergists also were non‐toxic when applied alone. The doses of carbaryl and synergist in different combinations that gave 50 % mortality (LD₅₀) were estimated. A simple form of graphical analysis revealed a common pattern in the results for 18 of the synergists. This indicated that if the mechanism that detoxifies carbaryl and that was depressed by these synergists was completely inhibited, the LD₅₀ for carbaryl would be about 0.06 μg per fly. Moreover, the analysis enabled relative potencies for these synergists to be estimated on a simple and rational basis, and showed a 700‐fold difference between the most and the least active. The significance of these and the remaining results is discussed in the light of the probable factors affecting the mode of action of the synergists.