Characterization and in silico and in vivo insecticidal effects of marjoram essential oil and its nanoemulsion on Tribolium castaneum and Oryzaephilus surinamensis

Marjoram essential oil (MEO) exhibits notable insecticidal activity; however, its practical application in stored-product protection is constrained by high volatility, low aqueous dispersibility, and physicochemical instability. To overcome these limitations, a nanoemulsion formulation of MEO (MEO-N) was developed using ultrasonic homogenization to enhance stability and bioefficacy. Physicochemical characterization included particle size and zeta potential analysis using dynamic light scattering (DLS) with a Zetasizer instrument and morphological evaluation by transmission electron microscopy (TEM), while chemical composition was determined by gas chromatography–mass spectrometry (GC–MS). MEO-N formed spherical nanoparticles with an average droplet size of 159 nm and a zeta potential of −19.1 mV, indicating good colloidal stability and uniform dispersion. GC–MS analysis identified carvacrol (43.07%), linalool (19.35%), γ-terpinene (7.53%), and terpinene (7.32%) as the principal constituents. Insecticidal activity was evaluated using a contact toxicity bioassay under controlled laboratory conditions against two major stored-product pests, Tribolium castaneum and Oryzaephilus surinamensis. MEO-N exhibited dose- and time-dependent insecticidal effects. In T. castaneum, 500 and 1000 ppm resulted in 43% and 56.67% mortality after 7 days, respectively. In O. surinamensis, 100% mortality was achieved within 120 h at 500 ppm and within 48 h at 1000 ppm. Molecular docking analysis revealed strong binding affinities of carvacrol and thujyl alcohol isomers to selected insect target proteins, suggesting potential molecular mechanisms underlying toxicity, while ADME/T predictions supported favorable bioactivity-related properties. Overall, the results indicate that MEO-N is a promising plant-based nanoformulation for the management of stored-product insect pests.