Cost and risk analysis of heat and chemical treatments.

An economic evaluation of newly developed methods for disinfesting empty grain storage bins by heat treatment will be a useful tool for decision-making by grain storage managers. An economic empirical model of heat treatment and chemical applications was developed using minimization of costs at a target risk level associated with the grain-damaging insects Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Rhyzopertha dominica (F.). Risk was measured as a deviation below a target mortality goal (Target MOTAD). Insect mortality and air temperature during heat treatment were evaluated for empty storage bins with a full drying floor, along with a similar evaluation of insect mortality for two application rates of a contact pyrethroid insecticide, cyfluthrin 20% active ingredient (AI) wettable powder. A high-output propane heater (29 kW) had the lowest cost and risk level of all heating systems and produced 100% mortality in 2 h for the three insect species at all test locations. An electric duct-heater system (18 kW) also produced 100% mortality at all test locations after 40 h, but it had significantly higher costs. The other heating system configurations in the study had significantly higher risk levels of insect mortality, and the electric systems were not cost-effective. Both chemical rates had low costs and risk levels, with high mortality results.