Antifeeding activity of isoquinoline alkaloids identified in Coptis japonica roots against Hyphantria cunea (Lepidoptera : Arctiidae) and Agelastica coerulea (Coleoptera : Galerucinae)

The antifeeding activity of 3 isoquinoline alkaloids identified from roots of Coptis japonica Makino toward 4th-instar larvae of Hyphantria cunea Drur y and adults of Agelastica coerulea Baly was examined using the leaf-dippin g bioassay. The biologically active constituents of the Coptis roots were c haracterized as the isoquinoline alkaloids berberine, palmatine and coptisi ne by spectroscopic analysis. In a test with H. cunea larvae, the antifeedi ng activity was much more pronounced in an application of a mixture of palm atine iodide and berberine chloride (1:1, wt:wt) at 250 ppm (82.3%) and 500 ppm (100%), compared with palmatine iodide (76.0%) and berberine chloride (75.4%) alone at 500 ppm. These results indicate a synergistic effect. With A. courulea adults, berberine chloride showed 57.5 and 91.1% antifeeding a ctivity at 125 and 250 ppm, respectively: whereas, weak activity was obtain ed in application of 500 ppm of palmatine iodide (41.4%) and coptisine chlo ride (52.4%) alone. The Coptis root-derived compounds merit further study a s potential insect-control agents.