2-Oxo-carotenoids, 2-Hydroxy-carotenoids, [uC]/β-Carotene, Metabolism, Stick Insects The carotenoids of the stick insect, Ectatosoma tiaratum, were studied by spectroscopic and chemical methods. The β,β-type pigments are β,β-carotene, β,β-caroten-2-one, β,β-caroten-2-ol, β,β-carotene-2,2'-dione, 2'-hydroxy-β,β-caroten-2-one, β,ε-carotene-2,2'-diol, 3,4-didehydro-β,β-carotene-2,2'-dione, 2'-hydroxy-3,4-didehydro-β,β-caroten-2-one, and 3,4,3',4'-tetradehydro-β,β-carotene-2,2'-dione. In addition, the following β,ε-type pigments were identified: β,ε-carotene, β,e-caroten-2-ol, and β,e-caroten-2-one. This is the first report on the occurrence of β,e-caroten-2-ol in an animal and of β,ε-caroten-2-one in nature at all. On treatment with BF3 in chloroform β,ε-caroten-2-ol is dehydrated to a specific product with the proposed structure of 2,3-didehydro-4,7'-retro-β, e-carotene. The biogenesis of the β,β-type carotenoids from β,ε-carotene is demonstrated by feeding [14C]β-carotene to the insects. Radiolabel was incorporated into all major metabolites of this type. The metabolism of carotenoids in stick insects is discussed applying the "half-molecule sub strate" hypothesis to the enzymic transformations of the pigments.