Effects of Biosynthesized Silver Nanoparticles on Feeding Behavior, Selected Insecticide Resistance-Associated Gene Expression, and Permethrin Susceptibility in Anopheles gambiae : A Laboratory Study

Background: Insecticide resistance in Anopheles gambiae threatens malaria control. This study evaluated biosynthesized silver nanoparticles (AgNPs) derived from the endophytic fungus Aspergillus niger for their effects on mosquito feeding behavior, resistance-associated gene expression, and permethrin susceptibility. Methods: AgNPs were biosynthesized using cell-free extracellular metabolites of an A. niger isolate and characterized by ultraviolet–visible spectroscopy, transmission electron microscopy (TEM), dynamic light scattering, zeta-potential analysis, and Fourier-transform infrared spectroscopy. The nanoparticles were predominantly spherical, with mean TEM and hydrodynamic diameters of 25.6 ± 4.2 and 28.3 ± 5.1 nm, respectively, a polydispersity index of 0.21, and a zeta potential of −32.4 ± 2.8 mV. Adult A. gambiae were exposed to 0.1, 0.5, and 1.0 mg/L AgNPs. Results: AgNP exposure significantly and concentration-dependently delayed host-seeking, reduced feeding success and blood-meal volume, and decreased responsiveness to a standardized human-odor stimulus ( p < 0.001). Expression of the resistance-associated genes Cyp6m2 , Cyp6p3 , and Ace1 decreased by up to 71%, 66%, and 59%, respectively ( p < 0.001). Permethrin-induced mortality increased from 45.8 ± 5.1% in controls to 89.3 ± 4.2% at the highest AgNP concentration, indicating enhanced permethrin-associated mortality but not restoration of full susceptibility. Conclusions: Biosynthesized AgNPs altered behavioral and selected molecular endpoints and enhanced permethrin-associated mortality in resistant A. gambiae under controlled laboratory conditions. These findings provide laboratory-scale evidence supporting further investigation of fungal-derived AgNPs as potential adjuncts to vector control. However, operational effectiveness, environmental persistence, nontarget effects, ecological safety, and effects on malaria transmission were not evaluated and require validation in mechanistic, semifield, ecological, and field studies.