Sequestration and metabolism of host-plant flavonoids by the lycaenid butterfly Polyommatus bellargus

Larvae of the lycaenid butterfly Polyommatus bellargus were reared on leaves of Coronilla varia that are rich in flavone C-glycosides. Six flavonoids including isovitexin and isoorientin, as well as several of their congeners were isolated and identified by spectroscopic means. Comparative HPLC analysis of the host plant and of larvae, pupae, and imagines of P. bellargus indicated selective uptake of isovitexin versus isoorientin derivatives. Isovitexin-2 ''-O-xyloside was the major flavonoid detected in pupae and in imagines of P. bellargus. Several minor components were tentatively identified as quercetin- and kaempferol-O-glycosides based on their on line-UV spectra and by comparison with known standards. Since leaves of the host plant accumulate exclusively flavones, the flavonol glycosides are considered to be biotransformation products that are formed by the insects and/or by symbiotic bacteria. Imagines of P. bellargus caught in the wild exhibited similar flavonoid patterns compared to imagines reared in the laboratory. Within the imagines, approximately 80% of all flavonoids are stored in the wings (especially in the orange submarginal lunules), whereas the remaining 20% resides in the bodies. Female butterflies show a significantly higher flavonoid concentration than males. It is suggested that the sequestered flavonoids are involved in visual mate recognition.