The ethanolic extract from Flourensia oolepis aerial parts showed strong antifeedant activity against the pest larvae, Epilachna paenulata, with an antifeedant index (Al%) of 99.1% at 100 mu g/cm(2). Based on chromatographic fractionation of the extract, guided by bioassays on E. paenulata, the flavanone pinocembrin (1) was isolated as the most active principle. In a choice assay, compound I showed strong antifeedant activity against E. paenulata, Xanthogaleruca luteola and Spodoptera frugiperda with an Al% of 90, 94 and 91% (p < 0.01) respectively, at 50 mu g/cm(2). The dosages necessary for 50% feeding inhibition of the insects (ED(50)) were 7.98, 6.13 and 8.86 mu g/cm(2), respectively. The feeding inhibitory activity of 1 against E. paenulata was compared with the activity of other structurally related flavonoids like naringenin, which was inactive up to 100 mu g/cm(2), catechin which was nearly 6 times less active than 1, and quercetin which was equally active as 1. The effect of these on the feeding behavior of E. paenulata was also studied. (C) 2009 Elsevier Ltd. All rights reserved.