Biotoxicity and repellency of Vitex negundo (L.) oil nanoemul- sion towards Rhyzopertha dominica (F.) on stored rice

Rhyzopertha dominica F. (lesser grain borer) is an important primary pest of stored rice that causes substantial economic loss. This pest developed resistance to a wide range of hazardous chemical pesticides due to its great degree of adaptability. This study proposed to prepare Vitex negundo oil nanoemulsion (VNO NE) to improve its efficacy against this target pest. Vitex negundo oil (VNO) contains key compounds such as 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-terpineol and Elemol. VNO NEs were prepared using a high-speed homogenizer from which nanoemulsion having 5% VNO mixed at a 1:2 (w/w) ratio with tween80 was found to be optimum considering different characterization parameters. The mean zeta potential, polydispersity index and hydrodynamic diameter of the nanoemulsion were -3.4 mV, 0.263 and 166.62 nm respectively. For contact toxicity lethal dose 50 (LD 50 ) value of VNO NE was 0.517 mu L cm -2 against R. dominica which was 46.03% less, compared to bulk VNO. LD 50 value of VNO NE for fumigant toxicity against R. dominica was 245.38 mu L L -1 which was 32.05% less than that of crude oil. The highest repellency increased by 30.14% than VNO, when treated with VNO NE in R. dominica . Significant inhibition of glutathione transferase enzyme was also detected in insects treated with VNO NE than VNO and control. These results indicated that VNO NE is an effective novel pesticide that can be recommended for the management of R. dominica in stored rice.