Standard bioassay method using insects for quality control of Bacillus thuringiensis products: The history and problems
2006
Asano, S.
For more than 50 years, a variety of Bacillus thuringiensis (Bt) products have been utilized worldwide as microbial insecticides. Early quality control of Bt products was based on spore counts in each formulation. However it was demonstrated later that spore counts do not always correlate with the insecticidal activity of Bt products and hence the bioassay using insects became a prerequisite for the quality control. The standardization of the bioassay method was discussed at the international meeting in 1966, where the standard product, E-61, was assigned as 1,000 International Unit (IU)/mg and the potency of each Bt product was to be expressed in IU/mg based on comparison of LC50 between the product and the standard. Thereafter the standard bioassay method has been employed among different countries. However some problems on the standardization still remain: Stock and supply of standard materials, storage stability of the standards, insect species and methods for bioassays, calculation of potency when sample and standard differed in insecticidal spectrum, criterion of acceptance for each product based on bioassay results, and development of easier and faster bioassay method than the present one. The author reviews the history of the standardization of bioassay methods and discusses existing problems in the quality control of Bt products.
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