A New Chitosan-Based Nanoformulation of Lavandula dentata Essential Oil for Sustainable Control of Green Citrus Aphids

The green citrus aphid (Aphis spiraecola) poses a serious threat to citrus production worldwide, primarily through the transmission of phytoviruses and the resulting yield losses in untreated orchards. Overreliance on synthetic insecticides such as Acetamiprid has led to increased resistance and environmental contamination (DT50 >120 days in soil). In this study, we present a novel nanoformulation of Lavandula dentata essential oils, chemically characterized by GC-MS, which is composed mainly of eucalyptol (12.8%), beta-pinene (5.7%), linalool (4.7%), camphene (4.4%), and alpha-pinene (4.0%). Nanoparticles were synthesized via optimized ionotropic gelation (0.4% chitosan in 1% acetic acid, 0.3% TPP crosslinking, 1500 rpm, 60 min), yielding a high production rate (83.6% +/- 1.2%), encapsulation efficiency (99.2% +/- 0.5%), and loading capacity (21.3% +/- 0.8%). Dynamic light scattering (DLS) revealed uniform particle sizes (41.8 +/- 3.1 nm) with excellent colloidal stability (+39.4 +/- 1.8 mV zeta potential, PDI 0.57 +/- 0.03). SEM imaging confirmed spherical morphology, smooth surfaces of nanoparticles, while unloaded controls appeared irregular and significantly larger (90.2 +/- 5.6 nm). EDX analysis further validated successful encapsulation, with oil-loaded particles showing a 6.7% increase in carbon content attributable to essential oil hydrocarbons, alongside preserved phosphorus signals from chitosan-TPP crosslinking. FTIR spectra exhibited characteristic peak shifts, including a 15 cm(-1) displacement of the carbonyl stretch (1740 cm(-1)) and the emergence of new P-O-C vibrations (930-950 cm(-1)), confirming the presence of molecular interactions. In controlled bioassays (25 degrees C +/- 1 degrees C, 65% +/- 5% RH), the nanoformulation demonstrated enhanced insecticidal activity, with LC50 decreasing from 0.43 mg/mL (48 h) to 0.25 mg/mL (72 h), representing a 42% increase in efficacy. Complete mortality (100%) was achieved at 0.5 mg/mL within 90 h, whereas unencapsulated oil lost 82% of its activity within 24 h due to volatility. The formulation also demonstrated excellent photostability (< 8% degradation after 72 h UV exposure) and low mammalian toxicity (OECD 208 LD50 > 2000 mg/kg), offering a sustainable solution with 3.8 times longer residual activity than conventional sprays. These findings establish chitosan nanoencapsulation as a promising strategy for enhancing the stability and effectiveness of botanical insecticides in integrated pest management.