PEA APHIDS AND MORE. “Buchnera reside in specialized bacteriocytes and are maternally transmitted to offspring: the aphid/Buchnera holobiont satisfies quite stringent reproductive criteria for Darwinian individuality. There are many other cases of insects associating with intracellular mutualistic bacteria for nutritional supplementation.”
http://www.pnas.org/content/112/33/10278.full