A tiny parasitic wasp injects a virus into ladybugs that turns them into zombie bodyguards for its young, a new study says.
The discovery of Dinocampus coccinellae's secret biological weapon, and its bizarre effect on the spotted lady beetle Coleomegilla maculata, reveals a devious new "mind control" strategy used by parasites. (Read "Mindsuckers" in National Geographic magazine.)
The newly described D. coccinellae paralysis virus (DcPV for short) marks the first known virus or other microorganism "involved in a behavioral manipulation that benefits another species," said study co-author Nolwenn Dheilly, a biologist at Stony Brook University in New York.
After being injected into the ladybug along with the wasp's egg, the virus replicates inside the growing wasp grub, which feeds on the insect's fluids.
Then, when the grub is ready to emerge and pupate, the virus infects the ladybug, causing paralysis.
Although the study team was able to detect the virus only in the ladybug's brain, "we believe it is able to infect the whole nervous system," said Dheilly, whose research appears February 11 in the journal Proceedings of the Royal Society B.
Once immobilized, the ladybug stands guard over the silk cocoon its former unwelcome guest has spun beneath it.
Since ladybugs are predators and contain toxic fluids, they make decent bodyguards, but the DcP virus may actually enhance their deterrent effect by making them twitch. (Related: "Pictures: Wasps Turn Ladybugs Into Flailing 'Zombies.'")
Dheilly thinks the virus is responsible for this twitching behavior, even if the link is yet to be demonstrated.
"Tremors are associated with many neurodegenerative disorders," she said. "Indeed, the virus load could directly participate in the duration of the paralysis and the tremors" seen in zombified ladybugs.
While a few parasitic wasps are known to use viruses as weapons, these so-called polydnaviruses are different from DcPV in that they're thought to help knock out the immune defenses of caterpillars and other host animals. (See more photos of zombie parasites.)
Another key difference is that polydnaviruses have co-evolved with their particular wasp species in such a close way that their DNA is integrated within the genome of the wasp. Given this, some scientists question whether such viruses can even be called viruses.
DcPV, in contrast, is a "free virus" and belongs to a group not previously known to manipulate hosts for the benefit of its parasite, according to Michael Strand, professor of entomology at the University of Georgia's Department of Genetics in Atlanta.
Strand, who wasn't involved in the new study, described the findings as "fascinating" and said that he suspects such viruses may be quite widespread.
But, he cautioned, the data presented in the study "do not definitively show that the alterations in host behavior are strictly due to DcPV."
Study co-author Dheilly concedes that more studies are needed to determine the exact roles of the virus and the wasp in controlling the ladybugs. (Also see "'Zombie' Roaches Lose Free Will Due to Wasp Venom.")
"It is probable that both DcPV and D. coccinellae are necessary to successfully trigger the bodyguard behavior," she said.
It's also unclear if the wasps are able reproduce successfully without DcPV, or whether their sinister alliance is one that wasp and virus both need equally in order to thrive.
Nor is it known if the virus has any negative impact on the wasps. Since all the wasps in the study tested positive for DcPV, "we don't know what a wasp looks like without the virus," added Dheilly, who conducted her research while at the University of Perpignan in France. (Explore an original interactive of mindsucking parasites.)
As for those ladybugs, it's not all bad news. Remarkably, despite having their insides eaten and then being zombified, around a third recover from their ordeal.