Blochmannia is a endosymbiont of sap feeding insects including aphids, mealybugs and psyllids. The Blochmannia live within specialized cells known as bacteriocytes and are transferred from mother to offspring. Blochmannia are considered to have established symbiotic relationships early in the evolutionary history of this group.
It is somewhat surprising to find Blochmannia in unrelated insect groups such as some ant species of the Camponotini tribe. Genetic analysis* finds that the Blochmannia in these ant species are most closely related to Blochmannia from mealybugs. Some ants in the Camponotini tribe live in close association with mealybugs that they tend to collect honeydew. It is possible that the Blochmannia was acquired by ants from mealybugs. Genetic analysis suggests a single successful movement of Blochmannia to ants. After making the jump from mealybugs to ants, the Blochmannia co-evolved with ants with new but closely related species of Blochmannia associated with closely related species of ants.
*Jennifer J Wernegreen, Seth N Kauppinen, Seán G Brady and Philip S Ward. One nutritional symbiosis begat another: Phylogenetic evidence that the ant tribe Camponotini acquired Blochmannia by tending sap-feeding insects. BMC Evolutionary Biology20099:292