Fig. 2. Undersides of female imagos of Polyommatus icarus. (A,B) Colour photographs, (C,D) ultraviolet photographs. (A) Individual reared on an artificial diet from which no flavonoids were sequestered. (B) Individual reared on the same artificial diet as in A, but with the flavonoid quercetin (2.5% dry mass) added. Only minor differences in wing coloration in the visible range are found between the diets. (C) Same individual as in A. The orange and black spots are highly ultraviolet-absorbing, the background is intermediate in ultraviolet reflectance and the white spots reflect most of the ultraviolet light. (D) Same individual as in B. The wing undersides absorb ultraviolet light effectively, with the white spots being almost indistinguishable from the background coloration. A gradient towards higher ultraviolet reflectance is visible from anterior to posterior in the forewings. A grey scale of known reflectance was included in every photograph (Mean spectral reflectance in blocks from 300nm (dark) to 400nm (light): 0.1%, 9%, 18%, 32%, 62%, 78%). Scale bars, 10mm.