Have you ever had another organism growing inside of you? Has that organism at some point burst out of you? Then, have you found yourself behaving in a zombie-like fashion – feet shuffling, eyes drooping, clumsy movements – protecting that organism with your very life?
If so, then take comfort in the knowledge that you are not alone. The spotted ladybug, Coleomegilla maculata, suffers from a tortuous form of parasitism by the wasp Dinocampus coccinellae. The wasp, upon finding a ladybug, injects it with an egg. This egg then grows up inside the unsuspecting ladybug. Eventually, the new wasp (still in larval form) “exits” the ladybug. Apparently, growing by eating the insides of the ladybug is not enough for the developing wasp, because once it exits its host, it forms a cocoon between the ladybug’s legs, using the ladybug as a shield against predators. The ladybug, ecstatic at such an opportunity to serve its master, does not try to abandon the cocoon, mostly remains motionless, and even occasionally wiggles its body to ward off predators. This behavioral manipulation of the ladybug is impressively specific, not starting until the wasp larva has exited the ladybug and begun making its cocoon.
Until recently, no one knew how the wasp managed to manipulate the ladybug in such an extraordinary fashion. Dheilly et al. (2015) studied the wasp-bug system, and found that a virus transmitted by the wasp may engender the behavioral alterations. The authors found that these wasps carried a newly identified virus, called D. coccinellae paralysis virus, which is transmitted to the ladybug through the injected wasp egg. Initially, the virus or the larva repressed the ladybug immune response, allowing the virus to spread in the bug, including into nervous tissue. Then, when the ladybug’s immune response reasserted itself, as it fought the virus, it caused collateral damage to the nervous tissue. The authors discovered that this nerve tissue damage correlated with the induction of altered ladybug behavior (which the wasp larva used to turn the ladybug into a bodyguard), and clearance of the virus correlated with the resumption of normal behavior (miraculously, some ladybugs survive this entire monstrous process, and continue living their lives!). It is not yet clear whether larval exit triggers the resumption of the ladybug immune response, or if the larva merely times its exit appropriately. Either way, in a manner reminiscent of biological warfare, the wasp is apparently using a virus to create zombies! Glad I’m not a ladybug.
Dheilly, N.M., Maure, F., Ravallec, M., Galinier, R., Doyon, J., Duval, D. et al. (2015). Who is the puppet master? Replication of a parasitic wasp-associated virus correlates with host behaviour manipulation. Proceedings of the Royal Society Biological Sciences Series B, 282, Article No.: 20142773.