Nanoparticles for mosquito control: Challenges and constraints

Mosquito control programs are facing important and timely challenges, including the recent outbreaks of novel arbovirus, the development of resistance in several Culicidae species, and the rapid spreading of highly invasive mosquitoes worldwide. Current control tools mainly rely on the employment of (i) synthetic or microbial pesticides, (ii) insecticide-treated bed nets, (iii) adult repellents, (iv) biological control agents against mosquito young instars (mainly fishes, amphibians and copepods) (v) Sterile Insect Technique (SIT), (vi) “boosted SIT”, (vii) symbiont-based methods and (viii) transgenic mosquitoes. Currently, none of these single strategies is fully successful. Novel eco-friendly strategies to manage mosquito vectors are urgently needed. The plant-mediated fabrication of nanoparticles is advantageous over chemical and physical methods, since it is cheap, single-step, and does not require high pressure, energy, temperature, or the use of highly toxic chemicals. In the latest years, a growing number of plant-borne compounds have been proposed for efficient and rapid extracellular synthesis of metal nanoparticles effective against mosquitoes at very low doses (i.e. 1-30 ppm). In this review, we focused on the promising potential of green-fabricated nanoparticles as toxic agents against mosquito young instars, and as adult oviposition deterrents. Furthermore, we analyzed current evidences about non-target effects of these nanocomposites used for mosquito control, pointing out their moderate acute toxicity for non-target aquatic organisms, absence of genotoxicity at the doses tested against mosquitoes, and the possibility to boost the predation rates of biological control agents against mosquitoes treating the aquatic environment with ultra-low doses (e.g. 1-3 ppm) of green-synthesized nanoparticles, which reduce the motility of mosquito larvae. Challenges for future research should shed light on (i) the precise mechanism(s) of action of green-fabricated metal nanoparticles, (ii) their fate in the aquatic environment, and (iii) the possible toxicity of residual silver ions in the aquatic ecosystems, (iv) the standardization of chemical composition of botanical products used as sources of reducing and capping metabolites, (v) the optimization of the green nanosynthetic routes, in order to develop large-scale production of eco-friendly nanomosquitocides.