THE INSECTICIDAL ACTIVITY OF SUBSTANCES RELATED TO THE PYRETHRINS

Abstract

The toxicity as contact insecticides of the esters of (±)‐3‐methyl‐2‐allyl‐cycfopent‐3‐en‐4‐ol‐i‐one with the natural (+)‐trans and with synthetic (±)‐cis‐trans‐chrysaii‐themum monocarboxylic acids has been compared with that of the natural pyrethrins. The comparison was carried out on five species of test‐insects.It was found that the figure for both the absolute and the relative toxicities of these compounds varied with the species used as test‐subject.The factors involved in this variation are discussed. The extremes of variation of relative toxicity for the compounds with the natural acid were from about one‐eighth as toxic as the pyrethrum standard when the aphid Macrosiphum solanifolii was used as test subject to nearly four times as toxic as the standard with the larvae of the moth Plutella maculipennis. The fully synthetic material varied from about one‐sixteenth as toxic as the standard to Macrosiphum solanifolii to nearly twice as toxic to the larvae of Plutella maculipennis. The compound with the natural acid was approximately twice as toxic as the fully synthetic material to three of the insect species, but the fully synthetic material was considerably more than half as toxic as the partially synthetic to the fourth test‐species. It is pointed out that while it is widely recognized that large differences in relative toxicity may occur when the effect of chemicals of widely different structure and mechanism of action are compared on a number of different test‐species, the fact that these differences may also occur with related chemicals with, presumably, a similar mechanism of action, has not been clearly stated.Even when the differences in relative toxicity are taken into account, the two synthetic pyrethrin‐like esters still show high insecticidal activity.It seems reasonable to suppose from the results that economic commercial synthesis of pyrethrin‐like insecticides is not impossible.