Development of new synthetic pyrethroids.

The insecticidal activity of synthetic pyrethroids was compared with that of the natural pyrethrins, which have been used on a world-wide scale as active ingredients for insecticidal aerosols or mosquito coils.All of the synthetic pyrethroids were found to be more stable than the pyrethrins. Tetramethrin showed a very high knock-down effect and resmethrin showed a remarkable kill effect in oil-based formulations. The efficacy of a suitable formulation of a mixture of tetramethrin and resmethrin surpassed that of natural pyrethrins synergized with piperonyl butoxide. For mosquito coils, allethrin and prothrin were superior to the natural pyrethrins in both kill and knock-down effects.Optically active synthetic pyrethroids always showed superior knock-down activity and higher killing activity than optically inactive compounds.