SIMULATING CHOLINESTERASE INHIBITION IN BIRDS CAUSED BY DIETARY INSECTICIDE EXPOSURE

We describe a stochastic simulation model that simulates avian foragin g in an agricultural landscape to evaluate factors affecting dietary i nsecticide exposure and to predict post-exposure cholinesterase (ChE) inhibition. To evaluate the model, we simulated published field studie s and found that model predictions of insecticide decay and ChE inhibi tion reasonably approximated most observed results. Sensitivity analys is suggested that foraging location usually influenced ChE inhibition more than diet preferences or daily intake rate. Although organophosph orus insecticides usually caused greater inhibition than carbamate ins ecticides, insecticide toxicity appeared only moderately important. Wh en we simulated impact of heavy insecticide applications during breedi ng seasons of 15 wild bird species, mean maximum ChE inhibition in mos t species exceeded 20% at some point. At this level of inhibition, bir ds may experience nausea and/or may exhibit minor behavioral changes. Simulated risk peaked in April-May and August-September and was lowest in July. ChE inhibition increased with proportion of vegetation in th e diet. This model, and ones like it, may help predict insecticide exp osure of and sublethal ChE inhibition in grassland animals, thereby re ducing dependence of ecological risk assessments on field studies alon e. (C) 1998 Elsevier Science B.V.