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• The spectral reflectance of the wings differed between adults reared on the native and alien plants. • Wild males preferred butterflies reared on the native host during the courtship process. -It was possibly because of differences in the spectral reflectance of the wings. • No difference in larval performance between individuals reared on the native and alien hosts • Alien plants can indirectly influence reproduction in endangered species Tongeia fischeri , a butterfly endangered in Japan, inhabits cliffs, riverbanks, rocky areas, and coastlines but has decreased in abundance owing to human-initiated habitat loss. This species’ larvae feed primarily on the native plant Orostachys japonica . However, they have recently been observed using alien Sedum species as hosts. We reared larvae on either the native host, O. japonica , or an alien host, Sedum sarmentosum , to compare life-history characteristics and the spectral reflectance of the wings. We also examined whether the species of larval host plant affected mating behavior. Female adults oviposited on both native and alien hosts, without a strong preference for either. No significant differences were found in larval period or pupal weight between the two hosts. The spectral reflectance of the hindwing underside differed between adults reared on the two host plants, particularly in the ultraviolet range. Subsequently, we evaluated the response of wild males to individuals reared on each of the two hosts. Live butterflies of either sex reared on the native host were contacted more often than those reared on the alien host. Males displayed more advanced mating behavior toward pinned dead specimens reared on the native host than toward those reared on the alien host. We concluded that the larval host plant affects the spectral reflectance of the wing and the mating behavior of T. fischeri , with males preferring individuals reared on the native host to those reared on the alien host, possibly because of the differences in wing spectral reflectance. This study provides evidence that alien plants as larval diet can indirectly influence butterfly reproduction.