Describing what might make the worst gift ever, researchers John McCutcheon and Carol von Dohlen report that they've found a system of symbionts resembling Russian nesting dolls. A tiny bacterium lives inside a slightly less tiny bacterium, which lives inside a mealybug. Unlike a nicely painted set of wooden dolls, though, each complete on its own, the matryoshka mealybug and its many inhabitants can't live without each other.
The citrus mealybug, Planococcus citri, is a a sap-sucking plant pest barely an eighth of an inch long. It's notable for destroying fruit crops and for being herded by ants, which fend off the mealybug's predators in exchange for eating its secretions.
As if being farmed by ants weren't insult enough, P. citri needs bacteria to live inside it and provide it with essential nutrients. Other symbiotic relationships have been observed between insects and bacteria, with insects sometimes harboring multiple bacterial species ...
