The Mechanism of Action of a Contact Insecticide

Abstract

In order to determine the method of entry of a contact insecticide such as pyrethrum into the body of an insect, studies were undertaken which showed that:—(a) The rapid penetration of the insecticide into the body cannot be effected through the cuticle.(b) When a mosquito has been sprayed with a mixture of pyrethrum extract and oleic acid, the deposition of fat globules around the tracheal trunks is a characteristic feature; this suggests that rapid diffusion of the insecticide takes place through the tracheal wall.(c) Experiments on flies with their spiracles closed indicate that the absorption of pyrethrum, either in the liquid and powdered states, was very slow. This fact indicates that normally pyrethrum enters the body through the spiracle.