Factors Affecting Penetration of Compounds Through the Cuticles of Insects and Mites

Abstract

A casual perusal of promotional literature for insecticides reveals that the efficacy characteristics attributable to formulation composition are rarely praised. Indeed, the relative merits of the product are often credited solely to the insect control agent. Although product differentiation by active ingredients has undoubtedly been commercially successful,even where compounds have many similar competitors, this approach may have blunted commercial pressure to optimise formulations for biological activity. Such a suspicion is aroused by concern in the industry that the considerable increases in laboratory potency of new insecticides are not reflected in comparative use rates of the formulated product in the field. Evidence for this disparity was first discussed by Hartley and Graham-Bryce (1980). Averaged over four pest insect species, the relative toxicity of DDT compared with deltamethrin in the laboratory was 1600 to 1. However, in field use the recommended ratio of active ingredient was 50 to 1. The endeavour to reconcile this disparity highlighted the extremely low utilisation of insecticides at the site of action, often 0.1%, after placement in the target environment. Graham-Bryce (1984) also suggested that the processes which attenuate the applied dose have proportionately greater effects as rates of application are reduced.