Fern-synthesized silver nanocrystals: Towards a new class of mosquito oviposition deterrents?

Mosquitoes act as vectors of devastating pathogens and parasites, representing a key threat for millions of humans and animals worldwide. Eco-friendly control tools are urgently required. We proposed a novel method of fern-mediated biosynthesis of silver nanoparticles (AgNP) using Dicranopteris linearis, acting as a reducing and capping agent. AgNP were characterized by UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), zeta potential and particle size analysis. In mosquitocidal assays, the LC50 of D. linearis extract against Aedes aegypti ranged from 165.213 (larva I) to 255.055 ppm (pupa). LC50 of D. linearis-synthesized AgNP ranged from 18.905 (larva I) to 29.328 ppm (pupa). In the field, the application of D. linearis extract and AgNP (10 × LC50) led to 100% larval reduction after 72 h. Smoke toxicity experiments conducted against A. aegypti adults showed that D. linearis leaf-, stem- and root-based coils evoked mortality rates comparable to the permethrin-based positive control (58%, 47%, 34%, and 48% respectively). In ovicidal experiments, egg hatchability was reduced by 100% after treatment with 25 ppm of AgNP and 300 ppm of D. linearis extract. Interestingly, oviposition deterrent assays highlighted that 100 ppm of fern extract reduced oviposition rates of more than 65%, while 10 ppm of fern-fabricated AgNP reduced oviposition rates of more than 70% in A. aegypti (OAI were − 0.52 and − 0.55, respectively). Overall, our results highlighted that D. linearis-synthesized AgNP could be useful candidates to develop nano-formulated oviposition deterrents effective against dengue vectors.