Mode of Entry of Contact Insecticides

Abstract

INVESTIGATIONS now being carried out by us into the use of D.D.T. for the elimination of tsetse (Glossina spp.) have led to observations which have a bearing on the mode of entry of some contact insecticides. This problem seems generally to have been considered only in connexion with the usual methods of using contact insecticides, in which the object is to bring the poison, either by spraying or by dusting, into maximal contact with the general body surface of the insect. Mr. Napier Bax has pointed out to us an exception to this, for Tutin1, so long ago as 1928, does record an observation in which two Carabid beetles and a Cicindelid died after being placed in a dish previously sprayed with an emulsion containing a rape-oil solution of pyrethrum, after the emulsion had dried. Nevertheless, no general attention seems to have been paid to the mere contact of insects with a sprayed surface. Thus Roy and Ghosh2, discussing as recently as July 1944 various views on the mode of penetration of pyrethrum, and particularly those of Wigglesworth3,4, record observations which led them to the conclusion that pyrethrum normally enters the insect body through the spiracles.