Dipel and Bactospheine, the commercially available microbial insecticides based on Bacillus thuringiensis, have been tested against poplar defoliator (Ichthyura anastomosis Steph.) first in the laboratory then in the field. Both have shown their efficacy against the pest by giving complete mortality of larvae in 0.1% concentrations. The out-breaks of the defoliator can effectively be controlled without affecting the other biological control agents or the environment.