DEMANIR, a simulation model of insecticide resistance development and management Original Research Article

We have written a simulation model to predict the effects of various pesticide uses and insect management regimes on the frequency of susceptible and resistant insects using the modelling program VENSIM®. The model, DEMANIR (DEvelopment and MANagement of Insecticide Resistance), is based on the saw-toothed grain beetle, Oryzaephilus surinamensis (L.). DEMANIR enables simulation of various insecticide use patterns and management strategies of grain protectants (insecticides) to prolong their effective life. DEMANIR allows for the density dependent effects on reproductive rate and migration; effects of farm hygiene; variation in fitness levels between susceptible and resistant beetles. Protectant efficacy includes: time since treatment; insecticide resistance level and protectant application efficiency. The program settings can be varied for each simulation run. Each run simulates two years, with a harvest in each year and various clean-up (hygiene) and insecticide treatment strategies. Simulations indicate the proportion of resistant insects declines, but does not reach zero in the absence of organophosphate (OP) use. OP use reverses that trend, but unexpectedly does not eliminate all susceptibles. Untreated grain provided a ‘refugia’ for susceptible insects which slowed resistance development. The maintenance of such ‘refugia’ is discussed in terms of overall insecticide use, resistance management and grain protection.