Temperature manipulation and the management of insecticide resistance in stored grain pests: a simulation study for the rice weevil, Sitophilus oryzae

A previously published growth model is modified and used to investigate the effects of temperature manipulation upon the spread of a resistance gene in an infested grain storage under Australian conditions. Grain cooling is shown to have a pronounced effect upon the generation time of the insects and, therefore, upon the rate of spread of the resistance gene. In uncooled (32°C) grain, under the ‘worst-case’ conditions, with an initial gene frequency of 10 −2 and a resistance factor of 64, the gene frequency rose to 0.99 after a year of storage and the amount of insecticide needed to achieve control rose by a factor of 13. In rapidly cooled grain, the gene frequency rose to only 0.2 and the insecticide requirement by a factor of only 1.6. Where grain was treated with insecticide on the mistaken assumption that resistance was not present, the population increased by a factor of 15 000 after a storage period of 1 year at a constant 32°C but only doubled where rapid cooling was used. The consequences of the results for the management of insecticide resistance are discussed.