Activation of Pyrethrins in Fly-Sprays

Abstract

MOST mosquito- and fly-control sprays contain pyrethrins, so that, during the present shortage, methods of economizing pyrethrins are of considerable importance. One accepted method of effecting an economy is to add to the spray a small proportion (usually less than 5 per cent) of a material which although not insecticidal in itself yet has the property of making the pyrethrin spray a great deal more oeffective. Such non-toxic additions are commonly called adjuvants or activators; for example, iso-butylundecylenamide¹ and sesame oil². So far as we are aware, this phenomenon of activation has never been explained, and indeed certain observers have experienced difficulty in demonstrating its existence.