The inactivation of Bacillus thuringiensis subsp. israelensis toxin by mosquito larvae proteases liberated into the medium.

Crystal serine-proteases of B. thuringiensis subsp. israelensis were able to process the 28,000-dalton protein during crystal solubilization. On the other hand, solubilized crystal proteins were degraded during the larvicidal bioassay by the action of serine-proteases liberated by mosquito larvae into the medium, with loss of toxicity. However, proteins in intact crystals were protected from the action of these proteases. This resistance to degradation of crystals partly explains the observation that they are more toxic than solubilized crystal proteins.