Parameters Influencing Potency of Bacillus thuringiensis var. israelensis Products

Bioassays of products based on Bacillus fliuiingiensis var. isruelensis have been carried out according to standard protocols. These analyses revealed that the slopes of the- log-probit transformed concentration mortality curves of various pro-ducts were different from that of the international standards (IPS82 for B. tliuringiensis isruelensis). For statistical rea- sons, this invalidates the tests. Products giving various slopes of the concentration mortality burves will obtain different potencies when estimated at a LCgO level *an when estimated at PC50 level, as normally done. The LCg0 level is probably more relevant for the field effect. /Changing the median particle size of a product in a non destructive way'resdts in change of ' plope and LC50 and thereby potency. Therefore, potency of a product as measured in these (bioassays is not just a measure of the quantity of B. thringiensis isruelensis crystal protein present, but a function of product parameters like median particle size. Biochemical methods for quantification of toxin can therefore not relate simply to potency of the products obtained