If you didn’t already think that wasps are the epitome of evil, wait until you hear about the parasitoid species Dinocampus coccinellae. Twenty days after a female lays its eggs inside a poor unsuspecting ladybug, a single larva rudely bursts out from the beetle’s abdomen and spins a cocoon between its legs. What happens next is truly bizarre: The ladybird is effectively turned into a bodyguard, sticking to the cocoon like glue and remaining completely still apart from involuntary twitches and shakes that scare off predators.
Just how the wasp achieves this remarkable host manipulation has been somewhat of a mystery, but new research may have cracked the case. According to the study, the wasps actually have a partner in crime: a newly discovered virus. This pathogen, which is harmless to the wasp, targets the lady beetle’s nervous system and accumulates in the brain. The finding is interesting because it raises the possibility that other zombifying parasites might not be wholly responsible for their dirty work, and that some other well-known mind-manipulating species may also be enlisting the help of viruses.
There are enough wonderfully disgusting examples of parasites manipulating the behavior of hosts to make your skin crawl. Although these known parasites all exert different effects, they tend to have something in common alongside mind-manipulation: they end up killing the host. D. coccinellae, on the other hand, doesn’t always kill ladybugs; around a quarter survive. But what is particularly interesting is the wasp’s apparent exquisite timing. Despite the larva growing inside the host for almost 3 weeks, it only becomes paralyzed after the prepupa emerges. So how is this achieved? That’s precisely what parasitologists at the University of Perpignan set out to examine.
As described in Proceedings of the Royal Society B, after a thorough investigation, the researchers found that the brains of parasitized ladybugs were riddled with RNA sequences that weren’t found in healthy beetles. Further scrutiny revealed that these belonged to a newly discovered species of RNA virus, which they named D. coccinellae paralysis virus (DcPV). This is a symbiotic virus, meaning that both the virus and the wasp benefit from the relationship. The virus gets a vehicle to transmit it around, and the wasp gets a zombie babysitter.
The researchers believe that DcPV is transmitted to the wasp eggs, which then get passed into the ladybug victim. Strangely, the virus doesn’t do much for several weeks, where it then begins to accumulate in the ladybug’s brain. Seemingly perfectly, the beetle’s brain cells experience extensive die off around the time the larva bursts out, which incapacitates the beetle and induces this bodyguard-like behavior.
But the story doesn’t end there. The researchers believe that part of the reason the whole process is so well timed could be down to the beetle’s immune system, which seems to be suppressed as the larva is growing inside the host. When the wasp emerges, the host’s immune system gets kickstarted again which elicits a strong antiviral response, killing the infected cells and inducing temporary paralysis, just in time to shield the larva. Eventually, the virus is eliminated by the active immune system and the nerve cells are restored, which brings the beetle’s behavior back to normal, if it manages to survive.
[Via Proceedings of the Royal Society B, Science and The Scientist]
