Titrage et définition d'une unité biologique pour les préparations deBacillus thuringiensis Berliner

The caterpillars ofPieris brassicaeL. are used as test-insects in order to appreciate the efficacy ofBacillus thuringiensis preparations. A biological unity is used as a value of expressing the toxicity of these preparations. It is defined as the ratio between the L D 50 of a standard preparation and that of the test sample. In order to avoid the variation that occurs when the caterpillars have not always the same physiological conditions, a correction is made by using an ideal constant mortality curve of the standard preparation. This curve has been established on caterpillars being in very good physiological conditions.