The nature and structure of the white-reflecting underside 'scales' on the hind wing of Pseudolestes mirabilis (Odonata: Pseudolestidae)

Abstract

The Hainanese endemic damselfly, Pseudolestes mirabilis, is unique among the Odonata in having brilliant silvery-white reflective areas on the underside of the hind wings in mature males. The light reflected is easily seen to be several times brighter than that from normal white pruinescence. The hind wing upsides have a striking coppery appearance due to the filtering of light reflected from the inside of the reflective area through bright amber tinted wing membranes, colour which results from small amounts of melanin in those parts of the membrane. Visual signals are thus produced from both sides of the wing and may be used to advertise territory occupancy while perched, as well as having an obvious semiotic function in aerial agonistic displays between pairs of males. The structure consists of a deep layer of long, parallel, flat wax fibres, secreted from the faces of cross-veins in individual wing cells over the affected areas. This is a spectacular and novel mode of cuticular wax secretion. The structure adds about 23–27% to the mass of the hind wing, which may explain its unusual shape and shortness. However this character is also present in females, which lack the wax fibres, hence it may be an unusual example of an epigametic male trait being partially expressed in females.