Growth-inhibitory activities of 1-(disubstituted benzyl)-2-methylbenzimidazole derivatives against Bombyx mori larvae

Abstract

The increasing prevalence of pesticide-resistant insects underscores the urgent need for novel control agents. We previously demonstrated that 1-benzyl-2-methylbenzimidazole derivatives (BMBIs) exhibit insecticidal activities against silkworm (Bombyx mori), a lepidopteran model insect; however, their efficacy still needs to be improved. To address this limitation, we synthesized a series of 1-(disubstituted benzyl)-2-methylbenzimidazole derivatives (hereafter referred to as disubstituted BMBIs) as candidate insect growth regulators (IGRs) and evaluated their activities. Notably, the developed compounds exerted various effects, including acute toxicity and growth inhibition, with the timing and severity of lethality varying according to the substituent type and position on the 1-benzyl group. Moreover, several 2′,4′-disubstituted BMBIs exhibited pronounced larvicidal activity. At 10 µg/larva, 2′-Me-4′-Cl (2) induced 87% acute lethality and 7% growth inhibition, whereas 2′-Me-4′-Br (5) induced 40% acute lethality and 30% growth inhibition. Overall, the BMBI series exhibited diverse biological profiles consistent with effects on multiple molecular targets, including the disruption of insect hormonal pathways.