The action of pyrethroids in the insect central nervous system. I. Features of molecular structure associated with toxicity to cockroaches and to their giant fibre axons

摘要

AbstractTo investigate relationships between the molecular structure of pyrethroids and their mode of action, toxicities to adult male Periplaneta americana by topical application and injection were compared with toxicities to their giant fibre nerve axons. From the tests against intact insects it was concluded that: (i) although ED50S ranged from 0.04 to 65 μg/insect, each compound was equally toxic, with one exception, when administered by either route; (ii) esters of (1 R)‐cis‐ were more toxic than esters of the corresponding (1 R)‐trans‐3‐substituted‐2, 2‐dimethylcyclopropanecarboxylic acids; (iii) α‐cyano‐3‐phenoxybenzyl esters were more toxic than the corresponding 3‐phenoxybenzyl esters; (iv) changes in the alcoholic component of some compounds (particularly trans‐isomers of esters of 5‐benzyl‐3‐furylmethanol and esters of α‐cyano‐3‐phenoxybenzyl alcohol) affected a recovery phase in their ED50/time curves more than changes in the acid component; (v) the amount of recovery was positively correlated with molecular polarity. The concentration required to decrease the amplitude of the action potential of giant fibres by 30 in 1 h ranged from 0.26 μM for the most active compound to 100 μM for the least active. There was no clear relationship between neurotoxicity and toxicity to whole insects and little association between neurotoxicity and features of molecular structure. Neurotoxicity was, however, positively correlated with polarity. Giant fibre axons seem unlikely to be