STUDIES ON THE SYNERGISTIC EFFECT OF PIPERONYL BUTOXIDE AND ISOBUTYLUNDECYLENEAMIDE ON PYRETHRINS AND ALLETHRIN

Experiments are described to compare the toxicity of natural pyrethrins and allethrin, the completely synthetic homologue of cinerin I, and to show the effect of the two synergists, piperonyl butoxide and iaobutyl undecyleneamide (IN 930) on both these active ingredients, using a measured‐drop technique with Mucca domestiur L. the housefly, and a residual‐film technique with Cimex lectularius L. the bed bug. In the conditions of the experiment, pyrethrins were shown to be twice as toxic as allethrin to flies, and 5.5 times as toxic as allethrin to bugs. The two synergists were tested at several ratios to the two insecticides, ranging from 1 : 1 to 20 : 1. The results were plotted as series of log. concentration/probit regression linea. These were parallel for the bug tests; but in the fly tests, the slope of the line increased with a rise in the proportion of Synergist to insecticide. The estimated median lethal concentrations indicated, in all cases, that the toxicity increased with a rise in the ratio of synergist to insecticide, at least up to 20 : 1. However, the enhancement of toxicity was greatest for the smaller ratios and fell off as the ratio increased. Piperonyl butoxide was the more powerful synergist, increasing the potency of pyrethrins 5 times and allethrin 4 times to flies, and pyrethrins twice and allethrin 3 times to bugs, whereas IN 930 did not increase the potency of either ingredient more than twice to either test insect. The addition of piperonyl butoxide to residual films of pyrethrins greatly prolonged their effectiveness; but an experiment designed to investigate the effect of the synergist on the stability of this insecticide showed that this action, if it exists, must be slight.