Effectiveness of biosilica nanoparticles from eichhornia crassipes in the control of acanthoscelides obtectus

Abstract

The widespread use of synthetic pesticides in post-harvest pest management has raised significant environmental and human health concerns due to their persistence, toxicity, and the development of resistant pest populations. These challenges have increased the need for sustainable pest control alternatives. Eichhornia crassipes, a silica-rich invasive aquatic plant from Lake Victoria, is a promising source of biosilica for biopesticide production. This study evaluated the effectiveness of biosilica nanoparticles synthesized from E. crassipes in the control of Acanthoscelides obtectus, a major post-harvest pest of common beans. Prior to biosilica synthesis, the moisture content, dry matter, ash content, and biosilica yield of the plant material were determined. The synthesized biosilica was characterized using UV–Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (SEM–EDX), X-ray Diffraction (XRD), and ImageJ particle size analysis. Bioassays were conducted on three bean varieties (Narobean 3, Kanyebwa, and Nambale) using biosilica concentrations ranging from 1.25 to 50 mg per 10 g of beans over a 15-day period. Leaves produced the highest biosilica yield (5.14 ± 0.04 g per 100 g dry biomass), followed by roots (4.42 ± 0.04 g) and stems (3.48 ± 0.04 g), with significant differences among plant parts (p < 0.05). FTIR confirmed the presence of characteristic Si–O–Si and Si–OH functional groups, while XRD showed broad diffraction humps around 2θ ≈ 19.94 –22.06°, indicating predominantly amorphous silica. SEM revealed irregular, porous, quasi-spherical particles, and EDX confirmed silicon and oxygen as the dominant elements. ImageJ analysis showed mean particle diameters of approximately 99.44 ± 20.90 nm (leaves), 100.02 ± 15.10 nm (stems), and 100.05 ± 16.83 nm (roots), confirming successful nanoscale synthesis. Bioassay results showed similar final mortality rates for biosilica derived from leaves (50.6 ± 2.5%), stems (50.6 ± 2.0%), and roots (49.8 ± 1.0%). One-way ANOVA indicated that neither the biosilica source nor bean variety significantly influenced final insect mortality (p > 0.05). The study demonstrates that E. crassipes is a viable renewable source of amorphous biosilica nanoparticles with potential application as an environmentally friendly biopesticides for post-harvest pest management.