Insect culture and Bioassay Plutella xylostella larvae were collected from fields at Bangbuathong district, Nonthaburi province and reared on chinese kale leaves at 25+ 2
C, 13:11 h (L:D). Bioassay was conducted by no-choice leaf dipping method (Dadang, 1999) in a completely randomized block design. Four concentrations (0.5, 1.0, 1.5 and 2.0% w/v) of hexane, dichloromethane and methanol extracts were prepared from the respective crude extracts. Controls were acetone with 1% tween-80, the solvent used to prepare test solutions. Leaves of Chinese kale (2 cm) were dipped in different concentrations of the extracts separately for 1 min and air-dried. Thirty 3 instar larvae of P.xylostella each were released in plastic cups (10 ml capacity) containing either treated or untreated (control) leaf disks as one replicate. Three replicates were used for each concentration of the extract. All bioassays were kept at 25+ 2 C with a 13:11 h (L:D) photo period. Mortality was assessed after 24 h application and corrected if necessary by Abbott’s formula (Abbott, 1925).