Cassia oil as a substitute solvent for xylene for rotenone EC and its synergistic activities

Abstract

The purpose of this study was to screen essential oils as substitute solvents for rotenone emulsifiable concentrates (EC). Spodoptera litura (SL-1) cell and third-instar larvae of S. litura were used as the model system to evaluate the cytotoxicity of essential oils and synergistic effect of cassia oil with rotenone. The result of screening assay indicated that essential oil treatments led to reductions in cell viability in a time-dependent manner. The inhibition rates of the 15 essential oils were over 80% after SL-1 cells were treated with 200μg/mL essential oils for 48h. The solubility of rotenone in cassia, basil, and clove oils were 15.84, 6.86, and 5.48g/100g, respectively, much higher than their solubility in xylene. After 24h treatment, the rotenone and cassia oil mixture (1:35, w/w) featured half maximal inhibitory concentration (IC50) of 28.66μg/mL against SL-1 cells and median lethal concentration (LC50) of 513.33μg/mL against third-instar larvae of S. litura. The co-toxicity coefficients(CTCs) of rotenone and cassia oil mixture (1:35, w/w) against SL-1 cells and third-instar larvae of S. litura were 240.75 and 166.23 when treated for 24h, which indicated that cassia oil possessed good synergistic effect with rotenone. The cell membrane potential and membrane integrity test results showed that cassia oil induced potential hyperpolarization of SL-1 cell membranes and promoted accumulation of PI, indicated that oil-exposed membranes lose cell integrity. Morphological images showed that application of rotenone with cassia oil to SL-1 cells produced cell membranes with their contents leaking. Finally, high-performance liquid chromatography (HPLC) assays proved that cassia oil increases the absorption of rotenone. These findings confirmed that cassia oil has marked synergistic effect on rotenone and has strong potential as an alternative solvent for rotenone EC.