Fate of carotenoids in the closed living system of gall–gall wasp–parasitoid

Carotenoids play multiple roles in insects, including coloration and protection. Most insects can obtain carotenoids only from their diet. Therefore, carotenoids are proposed to reflect trophic chains and lifestyles of insects. We investigated the mini-ecosystem of a gall on a hawkweed Hieracium × robustum induced by the gall wasp Aulacidea hieracii (Hymenoptera: Cynipidae) that is attacked by parasitoid wasp Eurytoma cynipsea (Hymenoptera: Eurytomidae). The parasitoid larvae consume the gall wasp larvae that consume the gall tissues. We employed resonance Raman spectroscopy to trace the fate of carotenoids in living larvae and pupae of these insects. We showed that carotenoid composition in the parasitoid closely corresponds to that of its diet—the gall wasp. On the contrary, carotenoid composition in the gall wasp was independent of that in the gall tissues, and the carotenoid concentration increases as non-feeding larvae mature. Thus, A. hieracii is suggested as a candidate among insects to have the ability to synthesize and modify carotenoids. Our findings give rise to the question of the relevance of using carotenoids as markers of trophic flow in the gall community.