Evaluation of granular corncob formulations of Bacillus thuringiensis serovar israelensis against mosquito larvae using a semi-field bioassay method.

A semi-field bioassay method using commonly available laundry tubs evaluated efficacy and residual activity of 6 granular corncob formulations of Bacillus thuringiensis serovar israelensis against laboratory-reared late 3rd- and early 4th-instar larvae of Aedes taeniorhynchus introduced to the tubs. These formulations produced appreciable larval mortalities (up to 75%) for 9 days posttreatment, with indications of having more prolonged activity. The consistent posttreatment larval mortality trends and the elucidated efficacy differences between formulations suggest that this bioassay method for the granular formulations is reliable and reproducible.