Retinoid composition in the compound eyes of insects

Retinoids in the compound eyes of insects in ten orders were extracted by the oxime method and analysed by HPLC. Four geometrical isomers (13-cis, 11-cis, 9-cis and all-trans) of syn and anti retinal oximes, and syn and anti 3-hydroxyretinal oximes were separated in a single analysis by a stepwise eluent condition. The amounts of the two isomers, syn 11-cis and syn all-trans, were quantified. 11-Cis 3-hydroxyretinal was detected in six orders: Lepidoptera, Diptera, Coleoptera, Neuroptera, Hemiptera and Odonata, and retinal and 3-hydroxyretinal were found together in the compound eyes of some species of Coleoptera and Odonata. We conclude that early in their phylogeny, insects had the ability to use 3-hydroxyretinal as the chromophore of visual pigment. Peaks corresponding to syn 9-cis and 13-cis 3-hydroxyretinal oximes were observed on the chromatogram of extracts from fly heads and compound eyes of cicadas. Retinol and 3-hydroxyretinol were also analysed and quantified relative to retinal and 3-hydroxyretinal. Larger amounts of the alcohols than the aldehydes were found in the compound eyes of butterflies, hornets, cicadas and grasshoppers, which are diurnal insects. 3-Dehydroretinal has not been detected in insects.