Sequestration of host-plant-derived flavonoids by lycaenid butterflyPolyommatus icarus

Larvae of the lycaenid butterflyPolyommatus icarus were reared on inflorescences ofCoronilla varia andMedicago sativa, which are rich in flavonoids. Twelve different flavonoids (five compounds from the former and nine from the latter), including aglycones andO-glycosides of kaempferol, quercetin, and myricetin were isolated and identified by spectroscopic means. NMR and MS data for the new acylated glycoside kaempferol 3-O-6″-(3-hydroxy-3-methylglutaroyl)-β-D-glucopyranoside are reported. Comparative HPLC analysis of the respective host plants and of larvae, pupae, and imagines ofP. icarus indicated selective uptake and accumulation of kaempferol vs. quercetin and myricetin derivatives. The latter were excreted largely unchanged through the feces. Irrespective of the larval host plant kaempferol 3-O-glucoside was found as the major flavonoid in larvae, pupae, and imagines ofP. icarus, accounting for approximately 83-92% of all soluble flavonoids in adult butterflies. Within the imagines, approximately 80% of all flavonoids are stored in the wings (especially in the orange submarginal lunules), whereas the remaining 20% reside in the bodies. Feeding experiments with artificial diet demonstrated that the insects are able to form kaempferol 3-O-glucoside by glucosylation of dietary kaempferol. Possible functions of the sequestered flavonoids, especially for mate recognition ofP. icarus, are discussed.