How Parasitic Wasps Use Hijacked Viruses to Sterilize Their Victims

Parasitic wasps are nature’s body snatchers. They lay eggs inside living caterpillars, and their larvae slowly consume the host from the inside out. But here’s the twist: these wasps don’t just kill their victims they chemically castrate them first.

A new study reveals exactly how they pull off this biological heist, and it involves a domesticated virus, a fake enzyme, and a cellular protein that the wasps have learned to exploit like a master hacker finding a backdoor into a secure system.

The Setup Wasps That Weaponize Viruses

The wasps in this story species like Cotesia vestalis and Microplitis manilae are what scientists call endoparasitoids. Female wasps inject their eggs directly into young caterpillars like diamondback moths and fall armyworms. As the wasp larvae develop inside, they need the host to stay alive but not grow up and reproduce.

Here’s where it gets wild: these wasps carry a domesticated virus called a bracovirus, integrated right into their own DNA. When the wasp stings a caterpillar, she delivers both eggs and this viral payload. The virus doesn’t make the wasp sick it’s been co-opted as a weapon, passed down through generations like inherited biological software.

Credit: Model for a Cotesia vestalis bracovirus gene, CvBV_28 − 5, affecting host ecdysone signaling and L3/L4 ecdysis. During parasitization, CvBV particles were injected into P. xylostella larvae and then infect the different host tissues. CvBV_28 − 5 is responsible for the downregulation of ecdysone in the hemolymph of P. xylostella larvae by interacting with Raf in the prothoracic gland (PG), then downregulating ecdysone synthesis genes of P. xylostella larvae. Thus, the disappearance of the 20E peak before ecdysis leads to the change of expression of ecdysone response genes like E78, HR3, and HR4, as well as genes related to a series of developmental events of ecdysis: synthesis of cuticle lipid and cuticle proteins, degradation of cuticle proteins and cuticle pigmentation

The Molecular Sabotage

The viral weapon of choice is a protein called CvBV_22-9. It’s supposed to be a protein tyrosine phosphatase an enzyme that normally removes phosphate groups from other proteins to regulate cellular functions. But this one is a fake, a pseudophosphatase. It looks like it should do the job, but it doesn’t. Instead, it does something far more devious.

The target is Rad9A, a protein that’s part of the cell’s quality control system. Rad9A is a key member of the 9-1-1 complex, which acts like a cellular smoke detector for DNA damage. When cells divide rapidly like they do in developing testes to produce sperm Rad9A keeps watch to make sure everything goes smoothly.

When CvBV_22-9 binds to Rad9A, it doesn’t remove phosphate groups like a normal enzyme would. Instead, this binding triggers a death signal. The testicular cells activate their self-destruct program apoptosis and die en masse. No testes, no sperm, no reproduction. The caterpillar is effectively sterilized.

How We Know This Works

Researchers led by Zhizhi Wang at Zhejiang University figured this out through some clever experiments. They noticed that parasitized caterpillars showed massive cell death in their testes shortly after being attacked by wasps. Gene activity analysis pointed to CvBV_22-9 as the culprit, highly active right where the damage was happening.

When they knocked down the viral gene, the testes survived. Checkmate.

To confirm Rad9A was the target, they used CRISPR gene editing to delete it from moths. The results were dramatic: embryos died, or if they survived, they had malformed testes and couldn’t reproduce—exactly like the parasitized caterpillars.

The team even tested this in fruit flies. When they made fly testes produce CvBV_22-9, the cells started dying. Combine that with reduced Rad9A levels, and the destruction got worse. This suggests the vulnerability is shared across different insect groups—a common weak point that wasps have learned to exploit.

Why This Matters

This isn’t just a cool bit of natural history. It’s a window into how parasites manipulate their hosts at the molecular level, and it could have real-world applications.

The fall armyworm and diamondback moth are serious agricultural pests, causing billions in crop damage worldwide. Understanding how wasps naturally control these pests could inspire new biocontrol strategies—maybe engineered proteins or viruses that target pest reproduction specifically, without harming beneficial insects.

It’s precision warfare at the cellular level.

What makes this study fascinating is how it blurs the line between parasite and virus. The bracovirus isn’t an infection it’s a tool, domesticated over millions of years of evolution. The wasps carry viral genes in their own genome and deploy them like guided missiles.

And there’s still more to learn. How exactly does the CvBV_22-9 and Rad9A interaction trigger cell death without changing phosphorylation? Are there other pseudophosphatases lurking in other parasitic systems, waiting to be discovered?