Abstract
Guided by bioassay test results, we have isolated an antifeedant compound against the diamondback moth, Plutella xylostella, from the hexane layer of the extract of Andrographis paniculata. The compound was identified as 14-deoxyandrographolide. Although this compound is used as a medicine in Pharmacology, its antifeedant activity against insects has not yet been reported. The minimum effective dose (MED) of the isolated compound in suppressing the feeding of DBM larva was 100 μg/leaf disc. It was less potent than crude extract of the hexane layer (MED=30μg/leaf disc) and a subfraction 5-2 derived from this layer (MED=50μg/leaf disc). This result suggests that substance(s) other than 14-deoxyandrographolide are present in the hexane layer, and may also be contributing towards feeding suppression against the DBM larva. Commercially available andrographolide was also tested for its antifeedant activity and the result (MED=25μg/leaf disc) showed that it was more potent than 14-deoxyandrographolide.
