Antifeedant activities of secondary metabolites from Ajuga nipponensis against Plutella xylostella

Antifeedant activities of seven chemicals isolated from Ajuga nipponensis were examined in a bioassay against 3 rd instar larvae of Plutella xylostella. Five compounds (luteolin, stigmasterol, acacetin, 20-hydroxyecdysone and fraction 1) showed significant antifeedant activities, with the AFI50 values of 1935.02, 2515.94, 6589.58, 287.58, 2171.31µg/ml after 24h and 1853.20, 3812.24, 2581.43, 103.42, 1429.75µg/ml respectively after 48h of treatment. The synergistic effects of mixtures of secondary compounds were studied and antifeedant index was directly related to the component and the proportion of the mixture i.e., no synergism existed between luteolin and 20hydroxyecdysone mixture, but the values of CTC for fraction 1, stigmasterol, acacetin, luteolin and 20-hydroxyecdysone mixture were up to 627.07 and 111.72 after 24 and 48h, respectively. In addition, only apigenin showed effectiveness against Diamondback moth, with a high mortality percentage and low consumed leaf area when mixed with avermectins.