Toxicity of Stemona root against onion cutworm by using different contacting methods and solvents

Roots of Stemona tuberoso have been extracted by using fixed-bed contacting method with serial and parallel technique. In order to extract secondary metabolites from roots of Stemona sp., various organic solvents with different polarities were employed. Optimal solvents for the extraction of effective ingredients from root were determined. The results showed that in most cases the yields of crude extract were highest by using parallel technique rather than serial technique. The highest yields of crude extract by using both techniques were obtained with acetone, followed by water, ethanol, methanol, dichloromethane and hexane, respectively. Furthermore it was found that the L-a-b value and the total soluble solid (TSS) value in terms of degree Brix of crude extracts were different depending on choice of organic solvents. In particular, dichloromethane extracted more total soluble solid from plant material with both techniques, followed by hexane, ethanol, acetone, water and methanol, respectively. The biological activities of different crude extracts from S. tuberosa against Spodoptera exigua were experimentally determined. It was observed that the crude extract with highest toxicity to Larvae was obtained with high polarity solvents such as water, methanol and ethanol. The results suggested that water extract tested under high concentration could promote higher mortality. On the other hand, hexane extract caused approximately 30 % mortality with highest concentration at 15% w/w. Dichloromethane and acetone extract could be considered of similar efficiency.