Abstract
BackgroundThe 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.ResultsWith the laboratory mosquitoes, Moringa oleifera AgNP effected high mortalities of 88–100% (LC50 = 0.39 ppm; LC95 = 0.62 ppm) at 24 h post exposure except at the lowest concentration, while Ficus exasperate AgNP induced a 32–100% mortality (LC50 = 0.51 ppm; LC95 = 1.15 ppm) except at the lowest concentration. In the field populations, mortality in Moringa oleifera and Ficus exasperata was 23–93% (LC50 = 0.65 ppm; LC95 = 2.28 ppm) and 37–50% (LC50 = 1.51 ppm; LC95 = 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.ConclusionsOverall, 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.
Highlights
The interest in larvicides of plant origin is generally renewed in vector control because of their safety compared to synthetic larvicides
Larval control is a complement to major vector control interventions such as the use of long-lasting insecticidetreated nets (LLINs) and indoor residual spray (IRS) (Killeen, Fillinger, & Knols, 2002; WHO, 2017b)
Malaria vector resistance to permethrin and deltamethrin has been reported in various parts of Lagos State (Awolola et al, 2018; Fagbohun, Oyeniyi, Idowu, Otubanjo, & Awolola, 2019; Oduola et al, 2012)
Summary
The interest in larvicides of plant origin is generally renewed in vector control because of their safety compared to synthetic larvicides. There are concerns about the relative safety dose of these phytochemicals on non-target organisms which led to the development of plant derived nanoparticles. We examined the bioefficacy of low doses of two green synthesized nanoparticles on immature stages of Anopheles mosquitoes in Nigeria. The four classes of chemical-based control are Pyrethroids, Organophosphates, Organochlorines and Carbamates (Mazzarri & Georghiou, 1995) which are quite impactful when deployed (WHO, 2017a); their drawback is the emerging development of resistance in mosquito species (Liu, 2015). The concerns over chemical larvicides (physiological resistance by vectors, adverse environmental effects, high operational cost and community acceptance) necessitate sourcing for improved eco-friendly agents. To improve the efficacy of the larvicides, nanoparticles are incorporates as delivery agents, with sizes of 10–1000 nm, thereby making the larvicides more powerful even at low doses (Mondal et al, 2014)
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