Pigments called carotenoids are obtained through diet by many creatures in order to maintain healthy immune systems. Aphids are able to synthesize carotenoids on their own. Aphids share this ability with plants, and some fungi and bacteria. Only one other insect, the two-spotted spider mite, is thought to have this ability. Entomologist Alain Robichon discovered this property of aphids in a 2010 study. In 2012, he set out to find out why aphids would make such a metabolically expensive chemical. He found strong evidence that aphids use it for a process similar to photosynthesis. Aphids come in different colours depending on environmental conditions - cold favours green, optimal leads to orange, and large populations with scarce resources produce white aphids. The colours correspond to different levels of carotenoids. Green aphids have the highest concentration of carotenoids, compared to white ones, which have almost none. Robichon's lab found that aphids with more carotenoids have higher levels of [[ATP]]. Furthermore, orange ones produce more ATP when they are placed in light. When they are crushed and purifed for their carotenoids, the extracts absorb light and pass energy on.