Infected with a zombie virus, the worms climb to the top of the tree to dance, inviting the birds to eat them

In a subtle evolutionary mechanism, this virus has taken control of the host's brain and caused it to behave in spite of its life.

This is a portrait of a cotton bollworm (Helicoverpa armigera) the protagonist of our story today. Like many other caterpillars, the cotton borer has to go through a life cycle to reach adulthood, going from eggs to larvae, then to pupae, and finally to butterflies.

Cotton fruit borer.

Cotton borers have to go through a life cycle to reach maturity.

Cotton borer is its larval stage. During this stage, its task is to focus on eating a lot of leaves, filling up its stomach to prepare to burrow into the ground, sleeping and waiting for itself to become a pupae. But sometimes, scientists observe a very strange phenomenon:

Some cotton borers refuse to eat or drink, and when the day comes to go to the ground to pupate, it does not crawl down. Instead, the cotton borer climbed to the top of the tree and writhed there like it was "sick".

This is a very risky behavior for cotton borers. While they don't fall easily, "dancing" atop the treetops means that the bollworms are inviting themselves to the birds of the sky, who see them as a delicious meal.

So why are these cotton borers doing this?

Instead of climbing down to the base to pupate, the cotton borer climbs to the top of the tree and squirms.

You do not think unfairly for them but sin, not these worms just played "things" last night. Scientists have finally solved the mystery, according to a new study published in the journal Molecular Ecology.

And it's terrible from a cotton borer's point of view: They've been infected with a zombie virus. It was this virus that took control of the brain and caused the cotton borer to behave in such a way.

Zombie virus

It sounds like a horror movie, but this happens quite often in the insect world.

Researchers from China Agricultural University subjected them to tests and found that the worms were infected with a strain of virus called nucleopolyhedrovirus (HearNPV).

HearNPV virus.

Once infected, the HearNPV virus quickly took control of the cotton borers' brains and drove them to the top of the tree. Scientists think this behavior has a history of millions of years in evolution.

The HearNPV viruses do this so that after the worm dies at altitude, they can spread the virus with the wind and infect other hosts. Or when eaten by birds, the HearNPV virus can also transfer from cotton borers to birds.

At this time, the worms only do the same task as the virus transport bus to the airport to prepare for takeoff.

Virus hack cotton borer brain like?

Although HearNPV viruses have had a tradition of hacking cotton borer brains for millions of years, how that mechanism happened was not until recent research elucidated.

"Although many researchers have been interested in the mechanism by which parasites and pathogens control host behavior, there has been little in-depth study to pinpoint their exact characteristics," the researchers said. Research at the Agricultural University of China said.

"Here, we illustrate how HearNPV induces photoregulatory enhancement in H. armigera larvae, by hijacking the host's visual perception and triggering climbing behaviour, causing the larvae to become infected. died at high altitude".

A dead cotton borer on top of a tree.

It turns out that light, not altitude or gravity changes, is what the HearNPV virus uses to control the cotton borer's brain. Chinese researchers have done some experiments to confirm that.

In the first experiment, they installed a grid system with LED lights and glass tubes and inserted infected cotton borers into it. The higher the LED is placed, the higher the pest will climb. In contrast, when the LED was set low, it turned out that the worms infected with the HearNPV virus crawled down again.

The second experiment used cotton borers that had been blinded. As a result, when the host could not sense light, the HearNPV viruses could no longer control the cotton borer.

Chinese scientists have named this process phototaxis, or the way in which organisms aim for the Sun's light source.

"Since sunlight hits plants from above, phototaxis is a reliable mechanism [by which the virus can hack into its host], to ensure that infected larvae climb and die. at peak altitude," the study wrote.

Cotton borer is attracted to light after infection with HearNPV virus.

Not stopping there, Chinese researchers dig deeper by comparing the genetic differences between infected and uninfected cotton borers. They found six genes involved in light response were differentially expressed in individuals infected with the HearNPV virus. Finally, three genes involved in phototaxis were found.

The three genes are HaBL (the gene that detects short-wave light), HaLW (which detects long-wave light) and TRPL (the gene that converts light into electrical signals). When these genes are ablated in infected cotton borers, they are less likely to be attracted to the local light source and no longer climb to the top of the light source.

In short, the story of the virus-infected cotton borers being "stunned" to light shows us a strange host control mechanism of the parasites. This is a sophisticated survival tactic that the virus has accumulated over millions of years of evolution.

And if a virus that infects caterpillars can do that, maybe there is another strain of virus that infects humans that can do the same, which scientists will one day discover.