Nano-enabled plant fortification: green-synthesized SiO2 and emamectin benzoate nanoparticles synergistically boost maize defense and agronomic performance against Spodoptera frugiperda infestation

Abstract

Zea mays L., a globally vital C₄ cereal, is increasingly threatened by fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), a destructive and insecticide-resistant pest. This study developed a nano-enabled strategy integrating green-synthesized SiO₂ nanoparticles (GS-SiNPs) for plant fortification with nano-formulated emamectin benzoate (EMB-NPs) for enhanced insecticidal activity. Laboratory bioassays on 4^th-instar FAW larvae evaluated acute toxicity (LC₅₀ and LC₉₀) and detoxification enzyme activity. A field experiment in Egypt, autumn 2024 used a randomized complete block design to test two foliar sprays on maize in ten treatments with four replicates. Larval counts, leaf damage, anatomy, photosynthesis, leaf area (LA) plant^-1, Si content, and yield were assessed. Laboratorially, LC₉₀ (ppm) values were 93.6 (EMB-NPs), and 122.7 (EMB bulk), with GS-SiNPs exhibiting the steepest (5.18). GS-SiNPs with EMB bulk or EMB-NPs exhibited LC₅₀ values of 102.0 and 71.8 ppm, respectively, indicating a synergistic effect of both mixtures. EMB bulk + GS-SiNPs and EMB-NPs + GS-SiNPs suppressed larval detoxification enzymes. Field results revealed 100% initial larval mortality. The ½EMB-NPs + GS-SiNPs reduced leaf damage by 64.2% after the 1^st spray, while ¾EMB-NPs + GS-SiNPs achieved 86.4% after the 2^nd spray. This treatment also induced significant anatomical modification, increasing blade, midvein, and vascular bundle thickness. It enhanced photosynthesis, leaf Si, and LA plant^-1, and boosted yield by 54.5% vis-à-vis control. Combining GS-SiNPs with EMB-NPs, particularly ¾EMB-NPs + GS-SiNPs, enhanced EMB bioefficacy and suppressed FAW detoxification while improving maize's physio-anatomical resilience. This nano-enabled sustainable strategy offers a dose-efficient and eco-friendly approach for FAW management and maize productivity.