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You can keep building your STEM skills at Brilliant.org/SciShow with 20% off an annual premium subscription! [♪ INTRO] These days, most of us can agree that contracting a virus is generally a bad thing. So you could imagine that in most species, parents would want to protect their offspring from viruses.

But among certain parasitic wasps, passing a virus to their offspring is the key to the species’ survival. One of these wasps is a tiny, non-stinging insect that lays its eggs inside fruit fly larvae. Now, this may sound like a weird place to put babies, inside another creature.

But it can actually work out great. The babies get a safe place to develop with a constant food source… as long as they can avoid getting killed by the host’s immune system. And these wasp eggs can.

Adult wasps turn fruit fly larvae into hospitable hosts by infecting them with a type of virus called a pox virus. This pox virus is in the same family as smallpox, but it’s specific to insects. The wasps in the species are generally all infected by it, but it’s evolved to be harmless for them.

Fruit flies aren’t so lucky, though. Each time a female wasp lays her eggs in a fruit fly larva, she also injects the virus into it with her venom gland. Inside the larva, the virus multiplies and spreads.

Soon, it completely overpowers the host’s immune system. And that’s what makes it possible for the wasp eggs to develop in peace. Under different circumstances, the larva’s immune system would identify the eggs as foreign objects and kill them.

But while it’s overrun, it can’t do a thing. The wasps eventually hatch and continue developing inside the larva, feeding on their host until all its tissue is gone. Once they’re mature, they emerge as adults, and their host larva dies before ever becoming a fruit fly.

Now, even though this symbiotic relationship seems to work out for the wasp and the virus, exposing vulnerable offspring to a dangerous virus still might sound like a bad thing. And to be clear, it’s not like the wasp knows it has a virus, or is thinking about whether that virus is good or bad for its babies. It’s just doing what it evolved to do.

But fortunately, both species have evolved to the point where the virus is harmless to these wasps, even the baby ones. And oddly enough, for the wasp, immersing its offspring in the virus before they’re born may be crucial for its survival. In a 2022 study, entomologists at the University of Georgia found that, as the wasps develop and feed on the larva, they’re in constant contact with virus particles.

These accumulate on the wasp’s outside shell, also called a cuticle. And as the wasp larvae mature and develop venom glands, the virus particles get incorporated into them. The authors of this study believe that this is the main way the wasp is able to get enough virus to successfully overrun a fruit fly larva’s immune system as an adult.

They found that if the outside of the developing wasp was sterilized with bleach after being exposed to the virus, they lost their viral infection. And wasps without the virus weren’t nearly as good at ensuring their offspring had a nice larva to grow up in. This unusual relationship with a virus may not just be useful for wasps.

In the future, it could also be useful to us humans. That’s because the fruit fly host of these parasitic wasps can be major agricultural pest. And parasitoid wasp species are known for helping keep pest populations down in areas they live.

It’s a reminder of the many ways nature can inspire solutions to our problems, if we make the effort to understand it. Insects use viruses to protect their babies. And if insects keep coming up with new ways to stay alive, they could become infinite in number!

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Thanks to Brilliant for supporting this video and thank you for watching! [♪ OUTRO]