From the abstract: "Unexpectedly, we found that the aphid genome itself encodes multiple enzymes for carotenoid biosynthesis. Phylogenetic analyses show that these aphid genes are derived from fungal genes, which have been integrated into the genome and duplicated. Red individuals have a 30-kilobase region, encoding a single carotenoid desaturase that is absent from green individuals. A mutation causing an amino acid replacement in this desaturase results in loss of torulene and of red body color. Thus, aphids are animals that make their own carotenoids."
This would have flown right by my radar if I’d heard of it at the time. Carotenoids? OK, the root word is carrots, right. And they're important why?
Carotenoids are used in more than the eyes.
From the abstract: "The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. ... This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules."
No other animal makes its own carotenoids, much less uses them in photosynthesis. They studied ATP production in green, orange, and white aphids (with respectively smaller amounts of carotenoid pigment), and found that more carotenoid meant more ATP if an orange aphid was in light, not so much if not.
BTW, the green aphids were the orange ones bred at low temperature! The green ones didn’t show a drop in their (larger) ATP dosage in darkness. Which is odd. Apparently low (non-ideal) temperatures turn on extra carotenoid synthesis, which makes a kind of sense. It is expensive to make the chemicals: more of a strain in non-ideal circumstances, but it means a little more free energy in leaner times, provided they survive that long. In good times they just suck plant sap to their hearts' content. There's a little difference between the two studies that I'd like clarified: the first one found green aphids lacked a particular carotenoid that the red ones had. Maybe there are two different strains of aphids, or of green aphids.
If they are running a primitive photosynthesis system, it clearly doesn’t provide enough juice to keep them from attacking the garden.