Modes of entry of petroleum distilled spray-oils into insects: a review

Abstract

Petroleum oils are some of the oldest and safest pesticides in use. In spite of the numerous improvements achieved in oil technology, the mode of entry and the insecticide action mechanism of these products have been the subject of considerable debate and conjecture over many years. The literature reviewed suggests that insecticide oils can penetrate the insect body through the integument as well as through the tracheal system. Suffocation by spiracle blockage was held as the most accepted theory on its mode of action. However, an in depth analysis of the interaction between oils and insects body surface from a physical perspective suggests that suffocation occurs only when insects are over-sprayed or dipped in oil. Based on this analysis, it is more likely that when petroleum oils contact the insect surface, capillary forces and complex physical interactions take place in the cuticular layer, which lead to differences in the melting point and permeability of cuticle waxes. This in turn, alters the waterproofing properties of the cuticle and also leads to penetration of spray oils that can be carried to different lipophilic tissues. The changes in the cuticle caused by oils, which range from changes in melting point of the cuticular wax layer to cuticle dewaxing, strongly suggest cuticular penetration as the foremost mode of entry of insecticide oils.