Torulene (3',4'-didehydro-β,γ-carotene) is a

carotene The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the ex ...

(a hydrocarbon

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

) which is notable for being synthesized by red pea aphids ('' Acyrthosiphon pisum''), imparting the natural red color to the aphids, which aids in their camouflage and escape from predation. The aphids have gained the ability to synthesize torulene by

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the e ...

of a number of genes for carotenoid synthesis, apparently from fungi. Plants, fungi, and microorganisms can synthesize carotenoids, but torulene made by pea aphids is the only carotenoid known to be synthesized by an organism in the animal kingdom at the time of its discovery (2010). In 2012, the spider mite '' Tetranychus urticae'' was found to produce its own caretinoids using homologous genes, likely derived from similar fungi. In 2013, the ''Acyrthosiphon'' caretinoid synthesis genes were found to be present in aphid relatives, adelgids and phylloxerids.

References

Carotenoids Plant physiology Cyclohexenes {{hydrocarbon-stub