Nanoformulation of Dysphania ambrosioides essential oil in chitosan nanoparticles and O/W nanoemulsions for sustainable management of Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract

Helicoverpa armigera is a highly destructive agricultural pest with a strong ability to develop resistance to conventional chemical insecticides, making it urgent to find sustainable and environmentally friendly alternatives. This study evaluated the insecticidal potential of Dysphania ambrosioides essential oil (DAEO) against H. armigera and sought to determine whether nanotechnology-based delivery systems could improve its effectiveness. DAEO was formulated as chitosan nanoparticles (DAEO-CSNP) using ionic gelation and as oil-in-water nanoemulsions (DAEO-NE) by ultrasonic homogenisation. GC-MS analysis identified 19 components, dominated by ascaridole (Z) (48.33%) and p -cymene (33.83%). Both nanoformulations had nanometric sizes (266-291 nm), high encapsulation efficiencies (92-96%) and good colloidal stability, with CSNPs exhibiting a positive zeta potential (+40.49 mV). FTIR and SEM analyses confirmed the success of the encapsulation and the spherical morphology of the particles. The nanoformulations significantly improved wettability, leaf coverage and sustained release compared to free oil. Laboratory bioassays on third-instar larvae revealed superior insecticidal performance of the nanoformulations, with DAEO-NE causing up to 95.83% mortality within 4 days, whereas DAEO-CSNPs reached similar mortality levels over an extended duration, reflecting their controlled-release behavior. CSNPs also induced rapid toxicity by ingestion and strong inhibition of larval growth. Greenhouse trials on chickpea plants confirmed the superior performance of CSNPs, achieving up to 90% mortality on day six. Probit analysis revealed lower LC₅₀ values for CSNPs (0.47-0.60%) compared to nanoemulsions and free oil. Overall, nano-encapsulation and nano-emulsification significantly improved the stability, bioavailability and insecticidal efficacy of DAEO, confirming their potential application in integrated pest management programs against H. armigera. • First comparative study of chitosan nanoparticles and nanoemulsions delivering Dysphania ambrosioides essential oil against Helicoverpa armigera . • Nanoformulations enhanced stability, wettability, and sustained release compared to the free essential oil. • Chitosan nanoparticles induced rapid ingestion toxicity and strong larval growth inhibition. • Nanoemulsions achieved high mortality within short exposure times under laboratory conditions. • Laboratory and greenhouse assays showed higher efficacy and lower LC₅₀ values than free oil.