Strong resistance to phosphine in the rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae): its characterisation, a rapid assay for diagnosis and its distribution in Australia

BACKGROUND: The recent development of very high resistance to phosphine in rusty grain beetle, Cryptolestes ferrugineus (Stephens), seriously threatens stored-grain biosecurity. The aim was to characterise this resistance, to develop a rapid bioassay for its diagnosis to support pest management and to document the distribution of resistance in Australia in 20072011. RESULTS: Bioassays of purified laboratory reference strains and field-collected samples revealed three phenotypes: susceptible, weakly resistant and strongly resistant. With resistance factors of > 1000 x , resistance to phosphine expressed by the strong resistance phenotype was higher than reported for any stored-product insect species. The new time-to-knockdown assay rapidly and accurately diagnosed each resistance phenotype within 6 h. Although less frequent in western Australia, weak resistance was detected throughout all grain production regions. Strong resistance occurred predominantly in central storages in eastern Australia. CONCLUSION: Resistance to phosphine in the rusty grain beetle is expressed through two identifiable phenotypes: weak and strong. Strong resistance requires urgent changes to current fumigation dosages. The development of a rapid assay for diagnosis of resistance enables the provision of same-day advice to expedite resistance management decisions. (c) 2012 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.