A REDUCTIONIST APPROACH TOWARDS SHORT-TERM HAZARD ANALYSIS FOR TERRESTRIAL INVERTEBRATES EXPOSED TO PESTICIDES

Factors determining residual pesticide toxicity to insects were investigated using a published stochastic model which simulates the encounter and transfer of insecticide from treated plant surfaces to lepidopteran larvae and predicts the proportion of insects responding. The walking velocity of an insect, the proportion of pesticide transferred per encounter and its area of contact with the leaf surface have important influences on mortality following residual exposure. Formulae were tested against data sets describing the response of larvae of Spodoptera littoralis exposed to cypermethrin and deltamethrin ECs and adults of Coccinella septempunctata exposed to dimethoate EC. The prediction of residual uptake underestimated the observed transfer, but only at high concentrations of active ingredient. Concentration-dependent behavioral response were implicated in the shortfall. A simple hazard index based on contact area, track width, walking speed and tolerance to pesticide correctly predicted the ranking of susceptibility of three coleopteran species to residual deposits of insecticide. -from Authors