Effects of piperonyl butoxide on insecticidal potency

The effects of piperonyl butoxide on the toxicity to adult mosquitos (Anopheles stephensi List, and Aedes aegypti (L.)) and house-flies (Musca domestica L.) of pyrethrins, two synthetic pyrethroids, three organophosphorus compounds and their oxygen analogues, and three carbamates (Sevin, and both 3-isopropylphenyl and 3,5-di-isopropylphenyl N-methylcarbamate) were determined quantitatively. Solutions, in di-isobutyl ketone, containing insecticide alone and insecticide/ piperonyl butoxide mixtures in the proportion of 1:10 were applied topically to individual insects. A high degree of synergism was obtained only with natural pyrethrins and carbamates and house-flies, and the effect on the toxicity of these insecticides to adult mosquitos was much less pronounced. Insecticidal potency of the synthetic pyrethroids allethrin and dimethrin was influenced less than that of natural pyrethrins. Piperonyl butoxide antagonised the action of malathion in M. domestica, and to a slight extent in A. stephensi, but increased the toxicity of malathion and malaoxon to Ae. aegypti. It had little effect on the potency of diazinon and parathion and their oxygen analogues (diazinoxon and paraoxon) with the exception that it increased the toxicity of diazinon and diazinoxon to Ae. aegypti. The results are discussed in relation to the hypothesis that piperonyl butoxide inhibits detoxification in insects. From a practical point of view, they suggest that no great advantages would be derived from the addition of piperonyl butoxide to formulations of organophosphorus compounds and carbamates used for residual contact action against adult mosquitos.