Sequestration and distribution of flavonoids in the common blue butterfly Polyommatus icarus reared on Trifolium repens

Abstract

Larvae of Polyommatus icarus Rott. were reared on inflorescences of Trifolium repens. The three main flavonoid components of flower extracts, quercetin-3-O-galactoside, its 6″-O-acetyl derivative and myricetin-3-O-galactoside were isolated and identified by spectroscopic means. Individual extracts from larvae, pupae and imagines as well as extracts from exuviae, larval faeces and the host plant were analyzed by HPLC. Quercetin-3-O-galactoside was found to be the main component in P. icarus. Apart from this, only one additional plant flavonoid, tentatively identified as a kaempferol derivative on the basis of its online UV-spectrum, was also present in all developmental stages of P. icarus. Particularly in larvae the high percentage of flavonoids not detectable in extracts of T. repens suggested that P. icarus is able to metabolize dietary flavonoids. Dietary myricetin-3-O-galactoside was found to be selectively excreted. The flavonoid content of P. icarus correlated with the insects' dry weight and sex. Females contained about twice the flavonoid content of male imagines. This sex difference was significant both with regard to flavonoid amounts and concentrations and is considered to support the idea of flavonoids contributing to wing pigmentation and playing a role in intraspecific visual communication. Further support for this hypothesis comes from the analysis of dissected imagines revealing a distinct flavonoid distribution within the butterflies: 77% of the total flavonoid content of individuals analysed in this study were found to be located in the wings. Furthermore hindwings contained more flavonoids than forewings. Results are discussed in the context of earlier studies concerning P. icarus reared on three different fabaceous plants.