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Abstract:
The fine structure of the tracheal tapetum lucidum was investigated in six members of the diurnal lepidopteran family Pieridae. These observations were compared with the eye glow hue on intact eyes, the reflection colour of the incident illuminated tapetum and the distribution of the red screening pigments found in some receptor cells.
The eye glow hue of dark adapted pierid eyes appears dark red. Whereas in the speciesColias crocea, C. australis andGonepteryx rhamni the red eye glow is observed all over the eye, appear the uppermost 35 horizontal eye rows in the speciesPieris brassicae, P. napi andP. rapae turquoise to yellow-green. The reflection colour of the tracheal tapetum of all examined pierid eyes is, however, uniformly turquoise to yellow-green all over the eye. In addition no regional structural differences in the tracheal tapetum at the proximal end of the rhabdom were observed. One knows, however, that inPieris brassicae, P. napi andP. rapae in the ventral and medial part of the eye, inColias crocea, C. australis andGonepteryx rhamni in all ommatidia the four proximally located receptor cells 5–8 contain red screening pigment which is arranged close to and even within the rhabdomeric structures (Ribi, 1978a). These observations show that the red eye glow observed in various pierid butterflies depends on coloured retinula cell screening pigment and not on the tracheal and rhabdomeric structures. Morphological and functional aspects of the Lepidopteran tapetum lucidum and the role of the coloured retinula cell pigmentation are discussed.
