Virus that kills males is discovered in insects | ET REALITY


Scientists in Japan have identified a virus that selectively kills males, and it turns out that it is hereditary, creating generation after generation of all females.

The discovery, made in caterpillars and described Monday in The Proceedings of the National Academies of Sciences, is “strong” evidence that “more than one virus has evolved to selectively kill male insects,” he said. Greg Hurst, a symbiont specialist at the University of Liverpool in England who was not involved in the study. That could one day help control populations of pest insects and disease vectors like mosquitoes.

“I hope many more cases like this will be discovered in the near future,” he said. Daisuke Kageyamaresearcher at the National Agricultural and Food Research Organization of Japan and one of the authors of the study.

The virus was found by chance. Misato Terao, a research technician at Minami Kyushu University, was tidying up the campus greenhouse when she found unwanted intruders (fat green caterpillars) nibbling on impatiens. She collected them and, on a whim, dropped them off at the lab of Yoshinori Shintani, an insect physiologist who is Minami Kyushu’s resident insect keeper.

Dr. Shintani decided that the caterpillars (tobacco cutworms, a species of voracious pest and scourge of Asian agriculture) could be useful for feeding other insects. “It was almost a miracle” that they didn’t end up in the trash, he said. When he remembered them, several days later, he had about 50 adult moths and, unexpectedly, they were all female.

Acting on a hunch, he crossed the females in the greenhouse with male tobacco moths he found fluttering around the lights in his own house. The greenhouse moths had only daughters, as did their daughters and their daughters’ daughters. During 13 generations of moth descendants, only three had males.

Dr. Shintani and his colleague, Dr. Kageyama, quickly realized they had a “man killer” on their hands.

For decades, scientists have known that hitchhiking microbes, usually bacteria, can establish themselves in the gelatinous cytoplasm of insect cells. And through a process that is not very well understood, these microbes can be passed from mother to daughter.

Sometimes these microbial symbionts disrupt the host’s reproduction. From the symbiont’s perspective, “males are useless” because they cannot help spread the microbe, Dr. Kageyama said. Then the symbiote simply eliminates them. Wolbachia bacteria It can prevent male butterflies from being born. Other bacteria kill developing males before they hatch, reducing competition for females and giving them a fortifying snack: the eggs that contained their siblings.

Dr. Shintani’s team found that antibiotics did not nullify the males’ lethal effect on greenhouse moth progeny, so bacteria could not be responsible. Genetic analysis turned up telltale signs of a virus, but unlike any male killer ever seen before. Only two viruses have been documented that kill men; The virus discovered by the Japanese researchers, which they named SlMKV, appears to have evolved separately.

To confirm that the male killer was indeed infectious and hereditary, Dr. Shintani needed to squeeze some tobacco moths. He and his team mixed the bodies of pupae and adult moths with SlMKV and injected the resulting suspension into the bodies of uninfected pupae and moths. That worked: the next generation heavily favored women, and in subsequent generations, men disappeared completely.

Further experiments revealed how lucky researchers were in finding this male killer. While cold weather can be lethal to tobacco cutworms, SlMKV is vulnerable to heat, and the researchers found that the virus’ effect was diminished and eventually neutralized at higher temperatures. The native range of the tobacco cutworm is in the subtropics of China and Taiwan.

Scientists suspect that the mild climate in the caterpillar’s home acts as a perpetual fever, suppressing the lethal effect of the males. It was pure chance that Japan’s mild temperatures dropped into the “Goldilocks zone,” where SlMKV is active, and that scientists were able to notice the imbalance between the sexes in the greenhouse.

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

Anything researchers can learn about male killers helps advance the quest for the pest controller’s holy grail: a “female killer,” which could help combat invasive pests or disease-carrying species like mosquitoes.

According Anne Duplouy, an evolutionary biologist at the University of Helsinki who studies microbial symbionts in insects, time is running out for humans to learn from these temperature-sensitive microbes. As the climate changes, he said, “we’re probably losing a lot of these interactions” before they can be documented.

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