Parasitic Wasps Infected with Mind-Controlling Viruses

Parasite-NG-cover-550In November, National Geographic put a ladybug and a wasp on its cover. They made for a sinister pair. The wasp, a species called Dinocampus coccinellae, lays an egg inside the ladybug Coleomegilla maculata. After the egg hatches, the wasp larva develops inside the ladybug, feeding on its internal juices. When the wasp ready to develop into an adult, it crawls out of its still-living host and weaves a cocoon around itself.

As I wrote in the article that accompanied that photograph, the ladybug then does something remarkable: it becomes a bodyguard. It hunches over the wasp and defends it against predators and other species of parasitic wasps that would try to lay their eggs inside the cocoon. Only after the adult wasp emerges from its cocoon does the bodyguard ladybug move again. It either recovers, or dies   from the damage of growing another creature inside of it.

How parasites turn their hosts into zombie slaves is a tough question for scientists to answer. In some cases, researchers have found evidence suggesting that the parasites release brain-controlling chemicals. But the wasp uses another strategy: there’s a parasite within this parasite.

In the Proceedings of the Royal Society, a team of French and Canadian researchers now lay out the evidence for this strange state of affairs. As they studied this manipulation, they reasoned that the best place to look for clues was inside the heads of parasitized ladybugs. They discovered that the brains of these hosts were loaded with viruses. When the scientists sequenced the genes of the virus, they found it was a new species, which they dubbed D. coccinellae Paralysis Virus, or DcPV for short.

The scientists found DcPV in the wasps as well–but not in their brains. In female adult wasps, the virus grows in the tissues around their eggs. Once a wasp egg hatches inside a ladybug, the virus starts replicating inside it, too. The larva then passes on the virus to its host, and the ladybug develops an infection as well.

DcPV causes no apparent harm to the wasps, but the ladybug is not so lucky. The virus makes its way into the ladybug’s head, where it attacks brain cells and produces new viruses in pockets inside the cells. Many brain cells die off during the infection.

The researchers hypothesize that the virus is responsible for the change in the ladybug’s behavior. To get the ladybug to guard the wasp, the virus may partially paralyze its host, so that it becomes frozen over the parasite. Because the paralysis isn’t complete, the ladybug can still lash out against predators. But these may just be wild spasms in response to any stimulus. The bodyguard effect may grow even stronger as the infection robs the ladybug of the signals from its eyes and antennae. Closed off the world, its sole purpose becomes protecting its parasite.

The fate of a parasitized ladybug–to die or to walk away–may depend on how it handles a DcPV infection. In some cases, the virus may be fatal–possibly by triggering a massive immune response that kills not just the virus but the ladybug itself. In other cases, the ladybug’s immune system may eventually be able to clear the virus out of its system, letting its nervous system heal.

In either case, the bodyguard paralysis lasts long enough to protect the wasp while it develops into an adult. Whether the ladybug lives or dies doesn’t matter to the wasp–or to the virus. The new wasp carries a fresh supply of DcPV. If it’s a female, it will be able to use the virus to infect both its own young, and its ladybug slave.

In recent years, scientists have developed a deepening appreciation for the importance of our microbiome–of the bacteria and viruses that make our bodies their home. While some microbes invade our bodies, others reside inside of us and help keep us healthy. Parasitic animals have microbiomes of their own, and this new study suggests that they can use them for suitably sinister ends.

(For more information on the sophisticated tricks of parasites, see my book Parasite Rex.)

16 thoughts on “Parasitic Wasps Infected with Mind-Controlling Viruses

  1. Incredible yes but it is difficult to see how the behaviour could have arisen purely on the basis of natural selection or that genes could be coded for such a complex scenario.
    This is one of an increasing number of instances where our current theories of inheritance seem inadequate. If we do not truly know how a bird knows how and where to build a nest of its species, what chance do we have of understanding how these much more complicated behaviours
    arise and are pssed on?

    [CZ: Our own lack of knowledge or personal sense of disbelief is not a sufficient basis for drawing conclusions about how the world works. If I told you that a virus inside a parasite could make a host’s behavior change, you might tell me that was impossible. But here we can see that it really does seem to do just that. Saying that it’s impossible to imagine how it could have evolved is wrong in the same way.]

  2. Sounds more like a symbiotic relationship between the wasp and virus rather than a parasitic one. Also, what does this sentence mean?
    “The larva then passes on ladybug develops an infection as well.”

  3. “weaves a pupa around itself”

    NO! The wasp larva weaves a COCOON, then molts to the pupal stage. The pupa remains inside the cocoon until maturing and molting to the adult stage.

    [CZ: Thanks. Fixed.]

  4. Utterly fascinating. I agree with Steave, however, that the virus seems to act more like the wasp’s symbiont (not to say weapon) than a parasite.

    (Another typo alert: “The bodyguard effect may strengthened” => “may be strengthened”/”may strengthen”.)

    [CZ: Thanks! Fixed.]

  5. CZ was kind enough to respond to my comment but I think slightly misunderstood me. The point I was making was that our current explanations in terms of natural selection and genetic inheritance while giving a good starting point for the physical aspects of evolution, do not seem to account for behavioural aspects. What are the genetic mutations that can lead to this? It seems we do not have a genetic explanation of current behaviour, hence my reference to bird nests. What can be the intermediate stages of the behaviour and how were they inherited? These are issues in all behaviour but because this is an extreme example of intricate actions involving another species it raises the matter even more sharply. I do not say anything is impossible but that the current explanations may be inadequate.

  6. I haven’t heard of this before! It’s almost unbelievable and really quite scary.

    (Typo. Should “Closed off the world…” be “Closed off from the world…”?)

  7. Are there any observed activities in nature, other than human ones, that could be said to be “learning activities”? What I am asking is: are there any observed, seemingly useless/fruitless actions in the animal world that could be taken to be efforts to change a species or individuals predicament? We could presume that viruses that kill their hosts without effective or efficient means to infect another host would be in the development, or “learning” phase of their evolution. Maybe: “without viruses there would be no evolution”!

  8. Very interesting article!

    Its possible than a virus like this can be the cause of the alzheimer

    Some of the virus effects on human brain cells seem to be the same, massive death of cells causing loss of memory, lack of voluntary movement, involuntary spasms and finally death, all that because some cells on the human brain doesnt regenerate.

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