Eugenol nanoemulsion as bio-fumigant: enhanced insecticidal activity against the rice weevil, Sitophilus oryzae adults.

Nanoemulsion is a promising delivery system for delivering the plant bioactive molecules against insect pests. In this study, we aimed to prepare eugenol based nanoemulsions (EL-NE) by ultrasonication method to investigate its fumigant toxicity against Sitophilus oryzae adults and to analyse the residual characteristics of eugenol bioactive on the treated grains and beetles. In EL-NE preparations, 1:1 ratio of eugenol: Tween 80 combination with 5 min of ultrasonication at frequency of 10 kHz and 12 W power output was determined as optimal. In the optimized nanoemulsions, 19.21 to 42.82 d.nm range of mean droplet size, 0.50 to 0.77 range of polydispersity index and -21.80 to -29.83 mV range of zeta potential values were observed with respect to 2.5 to 10.0% of eugenol concentrations. After 72 h of fumigation, enhanced fumigant toxicities (3.5-11.2 fold) were observed against S. oryzae adults for the optimized EL-NEs compared to eugenol alone. Fumigant toxicity results revealed 14.40 µl/L air of least LC50 value for the 10.0% EL-NE. Persistence of eugenol was more (12.46%) in EL-NE treated wheat grains compared to eugenol alone treatments based on Gas Chromatography-Mass Spectroscopy analysis, which indicates the improved fumigation. This study results suggests EL-NEs as promising nano-biofumigant against the S. oryzae adults for eco-friendly Integrated Pest Management (IPM).