Effects of Insect-Growth-Regulatory Benzimidazole Derivatives on Cultured Integument of the Rice Stem Borer and Mitochondria from Rat Liver

The larvicidal activities of benzimidazole derivatives with a terpenoid side chain on the rice stem borer and the silkworm were compared with such in vitro activities as the growth inhibition of the cultured integument of the rice stem borer and the respiration inhibition of rat liver mitochondria. Each larvicidal activity is parallel with these in vitro activities. The comparisons of their activities with those of rotenone and diflubenzuron indicate that the benzimidazoles mainly acted as respiration inhibitors in their larvicidal activity as well as causing cuticular growth inhibition. The activity of 1-(3,7-dimethyl-7-ethoxy-2-octenyl)-2-methylbenzimidazole, the most potent compound tested as a respiration inhibitor, was found to be about 6-fold higher than that of rotenone. In the respiratory chain, the site between NADH and ubiquinone was blocked, indicating that the larvicidal benzimidazoles shared a mode of action with those of rotenone, piericidins, and ubicidines.