Methanol extracts of fresh leaves of Citrus plants induce oviposition behavior by females of the Citrus-feeding swallowtail butterfly, Papilio xuthus L. One of the oviposition stimulants was isolated from an extract of Citrus unshiu Marc, and identified as 6,8-di-C-β-D-glucopyranosylapigenin (vicenin-2). The methanol extract of C. unshiu was fractionated into ether, ethyl acetate, n-butanol and water layers by solvent extraction; oviposition activity was only in the aqueous layer, which was subjected to C18 reverse-phase column chromatography, separating activity into two fractions (A and C). Fraction C was rechromatographed, yielding fractions CA (inactive alone) and CB (containing compound I). Bioassays showed compound I (vicenin-2) and fraction CA were inactive individually but elicited distinct oviposition behavior when mixed. Glycosylflavonoids might have widespread significance as contact stimulants in the host-finding behavior of butterflies. Isolation of other oviposition stimulants from C. unshiu extracts is now in progress.