Mode of action of pyrethroids.

Since pyrethroids are potent neuropoisons, their mechanism of action on the nervous system can best be studied by means of electrophysiological techniques. The nerve excitation occurs as a result of changes in nerve membrane permeabilities to sodium and potassium ions, and therefore any effect of pyrethroids can be interpreted in terms of such permeabilities. Detailed analyses of the action of allethrin on the giant axons of the cockroach, the crayfish, and the squid performed by means of intracellular microelectrode and voltage clamp methods have revealed the ionic basis of the action of allethrin on the nerve.

Evaluation of compounds for insecticidal activity on adult mosquitos. 5. Toxicity to adult mosquitos and residual properties of some pyrethroids.

New pyrethrin-like compounds are compared with earlier synthetic pyrethroids and natural pyrethrins for intrinsic toxicity to adult mosquitos and for residual contact activity. Two of the compounds are at least as toxic as pyrethrin I to female Anopheles stephensi and Aedes aegypti. Residues of these compounds are very persistent in the dark or in very subdued lighting but they decompose on exposure to normal intensities of daylight and rapidly lose their insecticidal activity.