Discovery of a male-killing virus in insects

Discovery of a male-killing virus in insects

Scientists in Japan have identified a virus that selectively kills males, happens to be heritable, and creates generation after generation of all females.

The discovery, made in larvae and described Monday in the Proceedings of the National Academies of Sciences, is “strong” evidence that “more than one virus has evolved to specifically kill male insects,” said Greg Hirst, a symbiosis specialist at the University of California, California. selective”. Liverpool in England, which did not participate in the study. This could one day help control populations of insect pests and disease vectors such as mosquitoes.

“I expect that more similar cases will be discovered in the near future,” said Daisuke Kajiyama, a researcher at Japan’s National Agricultural and Food Research Organization and one of the study’s authors.

The virus was found by accident. Misato Terao, a technical researcher at Minami Kyushu University, was leveling a greenhouse on campus when she found unwelcome interlopers — fat green caterpillars — nibbling on her ficus sap plants. She harvested them and, on a whim, dropped them into the laboratory of Yoshinori Shintani, an insect physiologist who is Minami Kyushu’s resident insect man.

Dr. Shintani decided that caterpillars — tobacco worms, a type of predatory pest and scourge of Asian agriculture — might be useful for feeding other insects. “It was almost a miracle” that they didn’t end up in the trash, he said. By the time he remembered them several days later, he had about 50 adult butterflies, and unexpectedly, all of them were female.

Acting on a hunch, he raised females from a greenhouse using male tobacco moths he found fluttering around the lights in his house. Greenhouse butterflies only had daughters, and so did their daughters Daughters, and their daughters’ daughters. Over the course of 13 generations of moth offspring, there were only three males.

Dr. Shintani and his colleague Dr. Kageyama soon realize that they have a “male killer” on their hands.

For decades, scientists have known that parasitic microbes, usually bacteria, can take up residence in the jelly-like cytoplasm of insect cells. Through a process that is not well understood, these microbes can be passed from mother to child.

Sometimes these microbial symbionts mess with the host’s reproduction. From the symbionts’ point of view, “males are useless” because they cannot help spread the microbe, Dr. Kajiyama said. So the symbiote simply eliminates them. Wolbachia bacteria It can prevent the birth of male butterflies. Other bacteria kill developing males before they hatch, reducing competition for females and giving them a fortifying snack: the eggs carried by their brothers.

Dr Shintani’s team found that antibiotics did not stop the male-killing effect in the greenhouse moth’s offspring, so bacteria could not be responsible. Genetic analysis showed clear signs of a virus, but unlike any male killer seen before. Only two male-killing viruses have been documented; The virus discovered by Japanese researchers, which they called SlMKV, appears to have evolved separately.

To confirm that the male killer was indeed contagious and heritable, Dr. Shintani needed to squeeze some tobacco moths. He and his team mixed the bodies of pupae and adult butterflies with SlMKV and injected the resulting slurry into the bodies of uninfected pupae and butterflies. This solved the problem: the next generation strongly favored females, and in subsequent generations males disappeared completely.

Further experiments revealed how lucky researchers were to find this male killer. While cold weather can be fatal to tobacco worms, SlMKV is vulnerable to heat, and the researchers found that the virus’s effect was diminished and eventually neutralized at higher temperatures. The original habitat of the tobacco worm is in the subtropical parts of China and Taiwan.

Scientists suspect that the temperate climate in the caterpillar’s home acts like a perpetual fever, suppressing the male-killing effect. It was purely coincidental that Japan’s temperate temperatures fell in the “temperate zone” where SlMKV is active, and that scientists were thus able to observe the gender imbalance in the greenhouse.

Outside experts say the team’s discovery is a sign that viral male killers are more common than expected. Dr Hirst said the discovery could have implications for the control of other important agricultural pests to which the tobacco worm is closely related.

Anything researchers can learn about male killers helps advance the search for the holy grail of pest control: the “female killer,” which can help control invasive pests or disease-carrying species like mosquitoes.

According to Anne Duploy, an evolutionary biologist at the University of Helsinki who studies microbial symbioses in insects, time is running out for humans to learn from these temperature-sensitive microbes. With climate change, “we will likely lose many of these interactions” before they are documented, she said.

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *