Biosynthesis of Carotenoids in Insects: What We Currently Know?

Carotenoids primarily protect organisms from oxidative damage caused by excessive light and various metabolic reaction. Animals, i.e., organisms of the kingdom Animalia, generally have no ability to synthesize carotenoids de novo and have to utilize exogeneous carotenoids acquired from their diet. Whereas, since 2010, several insect species, e.g., the pea aphid (Acyrthosiphon pisum) and the goldenrod gall midge (Asteromyia carbonifera), as well as arachnids, e.g., the two spotted spider mite (Tetranychus urticae), have been revealed to retain carotenoid biosynthesis genes of fungal origin in the genomes. These biosynthesis genes were composed of lycopene β-cyclase/phytoene synthase (CrtYB) and phytoene desaturase (CrtI) genes. Functions of the carotenoid biosynthesis genes have also been clarified dominantly in aphids and spider mites. Chapter 3 shines a light on current findings by structural and functional analysis of the carotenoid biosynthesis genes contained in these arthropods, especially insect aphids. Lastly, this chapter reveals ecological importance in food chain of aphid origin involving the red dragonfly (Sympetrum frequens) and other predatory insects and arachnids.