Efficacy of dust formulations against pyrethroid-resistant <i>Cimex hemipterus</i> and susceptible <i>Cimex lectularius</i> (Hemiptera: Cimicidae): influence of exposure pathways and cuticle-mediated tolerance

Dust formulations are important alternatives for bed bug control, yet their efficacy against tropical bed bugs (Cimex hemipterus (F.)), which frequently exhibit pyrethroid resistance, remains poorly defined. We evaluated 2 desiccant dusts (CimeXa, diatomaceous earth [DE]) and 2 chemical dusts (DeltaDust, Drione) against 3 pyrethroid-resistant C. hemipterus strains with documented cuticle variation and compared them with a susceptible Cimex lectularius L. (Monheim). Bioassays simulated continuous exposure, brief (5 min) contact, sublabel (50% rate) application, and horizontal transfer. Desiccant dusts, particularly CimeXa (silica), consistently achieved rapid and complete mortality in resistant C. hemipterus, outperforming DE and pyrethroid-based dusts. Chemical dusts were more constrained: DeltaDust (deltamethrin) was largely ineffective, while Drione (pyrethrin + PBO + silica gel) killed susceptible C. lectularius rapidly (<1 h) but was markedly slower in resistant C. hemipterus, reflecting kdr mutations and cuticle-mediated tolerance. Reduced dosage and brief exposure prolonged survival times, and horizontal transfer produced the greatest delays, although both pathways ultimately resulted in high mortality. Strain comparisons revealed a susceptibility hierarchy (SEL_MY > PEN2_MY > KUL_MY), consistent with cuticle thickness, indicating that thickened cuticles delay desiccant activity under direct exposures. Importantly, the effect of cuticle thickness was minimized for CimeXa under horizontal transfer but persisted for Drione. By linking exposure dynamics with kdr and cuticle-mediated resistance, this study shows that chemical dusts remain strongly constrained by resistance mechanisms, whereas silica-based desiccants-despite delayed action in strains with thickened cuticles-retain superior reliability and represent the most effective dust formulations for sustainable bed bug management.