Larvicidal potential of two silver nano-particles (Moringa oleifera and Ficus exasperata) against laboratory and field strains of Anopheles gambiae (Diptera: Culicidae) in Lagos, Nigeria

Abstract

Background

The interest in larvicides of plant origin is generally renewed in vector control because of their safety compared to synthetic larvicides. However, there are concerns about the relative safety dose of these phytochemicals on non-target organisms which led to the development of plant derived nanoparticles. In this study, we examined the bioefficacy of low doses of two green synthesized nanoparticles on immature stages of Anopheles mosquitoes in Nigeria. Aqueous plants ( Moringa oleifera and Ficus exasperata) extracts were used in the biosynthesis. The prepared Ag-NPs were characterizations using Fourier-transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy, and scanning electron microscopy (SEM). Third and early fourth instars of known susceptible laboratory strains of Anopheles gambiae s.s. (KISUMU strains) and pyrethroid resistant field strain of An. gambiae were exposed to serial dilutions of 0.25, 0.5, 0.75, 1.0 and 2.5 ppm of each phyto nanoparticles. Moribund and dead larvae were observed after 24 and 48 h post exposure, and the results were analysed with descriptive statistics.

Results

With the laboratory mosquitoes, Moringa oleifera AgNP effected high mortalities of 88–100% (LC ₅₀ = 0.39 ppm; LC ₉₅ = 0.62 ppm) at 24 h post exposure except at the lowest concentration, while Ficus exasperate AgNP induced a 32–100% mortality (LC ₅₀ = 0.51 ppm; LC ₉₅ = 1.15 ppm) except at the lowest concentration. In the field populations, mortality in Moringa oleifera and Ficus exasperata was 23–93% (LC ₅₀ = 0.65 ppm; LC ₉₅ = 2.28 ppm) and 37–50% (LC ₅₀ = 1.51 ppm; LC ₉₅ = 391.64 ppm) respectively. There was no significant difference in mortality values between the laboratory and field strains ( P < 0.05) at both 24 and 48 h post exposure times.

Conclusions

Overall, the study demonstrates the bioefficacy and potential use of green synthesized nanoparticles, at very low concentrations for the control of Anopheles larvae even in areas where resistance to the current chemical insecticides have been reported.