Bioassay Methods and Their Problems in Evaluating the Toxic Activity of Bacillus thuringiensis to Lepidopterous Insects.

Bacillus thuringiensis has been utilized widely as one of representative microbial insecticides. The toxic activity of B. thuringiensis to lepidopterous insects has been evaluated based on mortality, feeding amounts or growth rates. The bioassay methods include leaf dip, diet incorporation and oral administration. Each bioassay method has merits and demerits in evaluating biological activity; therefore, it is important to select the most appropriate method depending on the purpose of the bioassay. Measurement of the response of insects such as rate of feeding reduction or growth retardation is also important to evaluate the sublethal activity of B. thuringiensis. The author reviews the bioassay methods and the problems in evaluating the biological activity of B. thuringiensis to lepidopterous insects.