A novel bioassay system for evaluating the toxicity of Bacillus thuringiensis israelensis against mosquito larvae

A bioassay system employing acutely toxic concentrations of a spore-crystal mixture of Bacillus thuringiensis subspecies israelensis against fourth instar larvae of Aedes aegypti (L.) is described. Individual larvae are separately exposed to toxin in glass-lined miniature wells or scintillation vials. This method is free from the deaths due to predation among larvae. Such larval deaths are commonly encountered in bioassay groups of 25 larvae as currently specified in the World Health Organization guidelines. Our method offers shortened testing time, increased accuracy, and improved statistical precision.