Vitex negundo L. oil nanoemulsion for the ecofriendly management of Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) in stored rice

Abstract

The widespread use of synthetic chemicals as storage protectants makes food hazardous, endangers human health and develops insect resistance. Hence, in the present study Vitex negundo L. oil nanoemulsion (VNO NE) was prepared to manage stored grain pests. V. negundo oil (VNO) had major compounds like Aromandendrene, Beta-caryophyllene, Squalene, 3-octen-5-yne,2,7-dimethyl-, (E)-, 5-(1-isopropenyl-4,5-dimethylbicyclo[4.3.0]nonan-5-yl)-3-methyl-2-pentenol acetate, Farnesyl bromide, 4-terpeneol and Elemol. A high-speed homogenizer was used to formulate nanoemulsions of VNO and studies on their physico-chemical and thermal stability revealed that, the optimum nanoemulsion had 5% VNO mixed at a 1:2 (w/w) ratio with tween 80 surfactant. The hydrodynamic diameter, polydispersity index and mean zeta potential of the nanoemulsion were 166.62 nm, 0.263 and -3.4 mV respectively and droplet sizes varied from 50 to 200 nm in transmission electron microscopy. Lethal dose 50 (LD50) values for contact toxicity of VNO nanoemulsion (VNO NE) were 0.755 and 3.131 micro L cm-2 against Sitophilus oryzae and Tribolium castaneum respectively which were 41.60 and 29.88% less compared to VNO. In case of fumigant toxicity, LD50 value of VNO NE was 322.28 micro L L-1 against S. oryzae which was 26% less than that of crude oil. Highest repellency increased by 33.33 and 36.58% when treated with VNO NE in S. oryzae and T. castaneum respectively. Also significant Glutathione s transferase enzyme inhibition activities observed in VNO NE treated insects as compared to VNO and control. Thus, VNO NE having improved efficacy and targeted delivery could contribute towards eco-friendly sustainable stored grain pest management in rice.