The triterpene compounds present in the rice-field weed, Ludwigia adscendens (L.) leaves were analyzed by the TLC, FT-IR spectroscopy and 1H NMR for evaluating the fractions secondarily functional as a chemical cue for attraction of the folivorous flea beetle, Altica cyanea (Weber). The flourescence of the triterpenes revealed the presence of greenish and yellowish compounds in TLC plates, and the FT-IR spectroscopy of the purified compounds showed the existence of - - OH stretch, - - aliphatic C - H, - C = 0, - C -H bend methylene and - C - H bending methyl groups, - - OH stretch, - - aliphatic - C - H, - C = O, - C - H bend methylene, - C -H bending methyl groups and -C -O stretch groups, respectively. The 1H NMR analysis of greenish and yellowish triterpene compounds revealed δ values within the range of 0.8558 – 1.2533 and 0.8550 – 1.2533 implicating the existence of tertiary methyl groups. Higher δ values (e.g. 7.7173, 7.5440 and 7.1671 for greenish, and 7.7155, 7.5350, 7.2640, 7.1866 and 7.1671 for yellowish triterpenes) also revealed the existence of alcoholic -OH connected to the CH2 group. Olfactory bioassays with greenish triterpene fractions showed significant (P < 0.05) attraction at 30 – 50 μg/ml concentrations, while these with all yellowish triterpene fractions showed 83.8 – 96.7% no response and 3.3 – 16.7% aversions of the female flea beetles. The control solvent, however, produced no response.
