An index of the intrinsic susceptibility of non-target invertebrates to residual deposits of pesticides.

Abstract

A full methodology for estimating the relative susceptibilities of non-target invertebrates to pesticide residues is given. Susceptibility is determined as an index, which is the ratio between an exposure function (based on walking track width, walking speed, and the proportion of the area covered by the insect that is contacted) and susceptibility (expressed as the species' topical tolerance distribution at endpoint), The exposure parameters for the index were derived for seven coleopteran predators which colonize temperate cereal crops. Susceptibility data for the synthetic pyrethroid insecticide, Deltamethrin, was then used to calculate the index of susceptibility for each species. The aphid predators were Pterosticihus melanarius (llIiger). Nebria brevicollis (F.). Agonum dorsale (Pont.), Demetrias altricapillus (L.), Bembidion lampros (Herbst.) (Coleoptera, Carabidae). Tachyporus hypnorum (F.) (Coleoptera.,Staphylinidae) and Coccinella septempunctata (L.) (Coleoptera, Coccincllidae). The indices indicated that the staphylinid beetle T. hypnorum would be most affected by deltamethrin residues because of its high susceptibility and high level of surface contact relative to body size. The least affected species would be the carabid beetle D. atricapillus, because it had a low susceptibility to deltamethrin and a small contact area with the surface. These predictions of extremes were confirmed in two residual bioassays. The uses and limitations of the susceptibility index are discussed.