Negative Cross-Resistance of Pyrethroid-Resistant <i>Aedes aegypti</i> Strains to the Benzimidazolium Derivatives: Virtual Screening, Synthesis, and Bioassay of the Potential Voltage-Gated Sodium Channel Blockers/Modulators

Negative cross-resistance (NCR) is an effective strategy for managing insecticide resistance. Haedoxan A (HA), a natural insecticide derived from <i>Phryma leptostachya</i><i>,</i> exhibits NCR with permethrin by targeting voltage-gated sodium channels (VGSCs). In this study, structure-based virtual screening, derivative synthesis, and biological evaluation revealed that compounds with a benzimidazolium skeleton show strong potential as sodium channel blockers/modulators. Among them, compounds <b>6i</b>, <b>LA-12</b>, <b>LA-26</b>, <b>LA-35</b>, and <b>LA-51</b> displayed an NCR profile similar to HA and potent mosquitocidal activities. Notably, <b>LA-49</b> boosted the highest larval toxicity against both pyrethroid-susceptible and resistant strains of <i>Aedes aegypti</i>, with LC₅₀ values of 0.403 and 0.940 μg/mL respectively, representing a 112.7- and 16.9-fold increase in potency compared to the lead compound <b>6i</b>. Its efficacy was comparable to HA (LC₅₀ = 0.338 and 0.301 μg/mL, respectively) and exceeded that of permethrin (LC₅₀ = 1.474 μg/mL) against the pyrethroid-resistant strain. The findings suggest that the benzimidazolium-based derivatives, characterized by simple chemical structure, synthetic tractability, potent activity, and NCR properties, represent promising candidates for further development in insecticide resistance management targeting VGSCs.