Rapid bioassay for determining the phosphine tolerance.

The resistance testing kit is an assay to receive very quickly detailed information about the behaviour of adult insects in a phosphine atmosphere. The used concentration of 3,000 ppm has a narcotic effect on non-resistant insects within a few minutes. Insects with a low phosphine susceptibility are still active after this time period. Using the resistance testing kit we succeed to distinguish between the tolerance of different insect species, the tolerance of one species at different concentrations and of different temperature regimes. The evaluation of different concentrations of phosphine, of their effectiveness against resistant strains of Lasioderma serricorne shows that at usual fumigation conditions resistant beetles can not be controlled with phosphine whereas at higher concentration 100 %-mortality of all development stages is achieved. Furthermore, longer exposure times have also a positive effect on the mortality of all development stages. The results confirm that the resistance testing kit is an effective device to recognize the resistance in an early stage, to fight against the development of resistance and to fight against the spreading of resistance. In future the resistance testing kit should be part of an integrated pest management system and a requirement for a good fumigation practice. Key words: resistance testing kit, resistance, phosphine, magnesium phosphide, stored-product pests.