DECISION SUPPORT SYSTEM FOR ECONOMIC-ANALYSIS OF GRASSHOPPER TREATMENT OPERATIONS IN THE AFRICAN SAHEL

A decision support system for benefit/cost analysis of chemical treatment of the Senegalese grasshopper, Oedaleus senegalensis (Krauss) (OSE), was created to assist in the training, analysis, and management of grasshopper treatment programmes. The system, known as GHLSIM, has linked simulation models, databases, and a user interface. Millet and sorghum phenology and yields are estimated by an FAO (Food and Agriculture Organization, United Nations) soil water deficit model. Outputs from the PRIFAS (Programme de Recherches Interdisciplinaire Francais sur les Acridiens du Sahel) OSE biomodel, including daily grasshopper life stages and favourability for development, are converted to density estimates using survey data, oviposition rates, and natural and insecticide-caused mortality. Crop loss is estimated through crop injury units - a function of grasshopper stage densities, consumption rates, crop preference, crop stage susceptibility, and non-crop vegetation greenness. Second-year benefits of treatment are estimated from end-of-season egg-pod densities. The model was calibrated using published economic thresholds for four crop stages. Yield increases from a late-season grasshopper aerial treatment campaign, 22 September - 19 October 1987, at 13 sites in eastern Chad were estimated at 33% +/- 20% (s.e.). Benefit/cost ratios were 2.6 +/- 0.5 for the first season, and 3.8 +/- 0.7 with second-year effects added. The analysis indicated that optimal timing was 5-10 days earlier than the actual treatments. Crop yield reports from treated and non-treated areas, a crop loss assessment conducted in Batha, Chad in October 1987 and a break-even analysis provide further evidence that the campaign was successful and cost-effective at most sites, as indicated by model results.