Phyletic aspects of the distribution of 3-hydroxyretinal in the class insecta

Summary The distribution of 3-hydroxyretinal (R₃), a recently discovered retinoid used as the visual pigment chromophore in some insects, was investigated in the class Insecta using HPLC technology. We studied 138 species in 24 orders, sampling from a wide range of taxonomic groups as well as varied habitats. In addition to groups already known to have R₃, we find this retinoid in Hemiptera (suborder Heteroptera), Plecoptera, Megaloptera, and Hymenoptera. We also find retinal (R₁) in Hemiptera (suborder Homoptera), Mecoptera, and Trichoptera, groups previously thought to have only R₃. The pattern of R₃ occurrence indicates that this retinoid cannot be considered a phylogenetic marker, having a scattered distribution in the class Insecta as well as within some orders of insects. Several environmental factors that might influence the selection of chromophore have been considered, but none correlates with its distribution. The evolutionary reasons for the pattern of occurrence of R₃ therefore remain unknown.