Carotenoid Biogenesis in the Stick Insect, Carausius morosus, during a Larval Instar

Carotenoids, Metabolism, [14C]/?-Carotene, Insects, Carausius morosus [14C]/?-Carotene was fed to juvenile stick insects, Carausius morosus, o f the fifth instar. Radio­ activity was incorporated into 2-hydroxy-, 2-oxo-, and 3,4-didehydro-2-oxo-carotenoids of the ß,ß-type. These transformations are due to the insect’s own capacity; any contribution by microbial symbionts can be ruled out. A study on the labelling kinetics clearly shows that the biogenesis of hydroxyand oxo-carotenoids is correlated to a decrease in the carotene precursor, but only up to mid instar. Thereafter, oxidation of the carotene is very low but the transformations of its metabolites continue as before. Predominantly ß,^-carotene-2,2'-diol is dehydrogenated to 3,4,3',4'-tetradehydro-/?,/?-carotene-2,2'-dione via two hydroxyketones. This discontinuous utilization of /7-carotene could be due to a stop at mid instar either in the oxidation or in the absorption in the gut of this precursor.