Ten newly synthesized quinazolinone Schiff base derivatives were tested under controlled conditions for their biological activity on the greater wax moth (Galleria mellonella L.). The biological oral test was conducted on the final larval stage. Mortality, behavioral changes (orientation test), symptoms of pathogenicity on the cuticle (color change, lesions, and spots), and the effect on insect development were monitored at 24, 48, 72, and 240 hours after treatment. The tested quinazolinone derivatives did not cause significant mortality in the insects nor did they affect their behavior. The highest number of larvae exhibited cuticle color change after 48 hours. The impact of the quinazolinone derivatives was most pronounced 72 hours after treatment. After 72 hours, all compounds induced pupation in the insects (ranging from 3.44% to 60% of the larvae pupated), compared to the control group, where no pupation occurred. More than 90% of the caterpillars pupated 240 hours after treatment for all compounds and in the control group. Compounds SB3, SB8, SB14, SB21, SB17, SB19, and SB25 should be further tested to investigate the biological activity of these compounds at different concentrations and under various ecological conditions, as well as on different insect species. This research established that quinazolinone derivatives have a broad spectrum of activity on the larvae of the greater wax moth, further confirming their potential as regulators of insect growth and development.