This study was conducted in the laboratory of postgraduate studies in the Department of Plant Protection / College of Agriculture and Forestry for the year 2019 and included a laboratory study to find out the effect of the bacterial Belthirul WP with some other auxiliaries on the percentage killing of larvae of the third and fifth ages of the great wax moth Galleria mellonella L. after different exposure periods. The results showed that the average percentage killing percentage with concentrations (1, 2, 3 gm/ liter) for the bacterial Belthirul WP, the exposure period for the third and fifth larval ages، and the overlap between the biocide concentrations, exposure periods and larval ages exceeded the concentration of 3 gm / liter significantly in the average killing ratios of third and fifth age larvae after 72 hours of treatment, it reached the highest average 100، 95.5% respectively. The results also showed the superiority of myrtle oil in compatibility with the bacterial biocide in increasing mortality percentages, as it reached 100 and 97% and after 72 hours of treatment for larvae of the third and fifth ages of the great wax moth, respectively.