Scientists in Japan have discovered a virus that specifically kills male insects and is inheritable, resulting in generations of all female insects.
The findings, published in The Proceedings of the National Academies of Sciences, provide strong evidence that multiple viruses have evolved to selectively eliminate male insects. This discovery has the potential to assist in controlling populations of pest insects and disease vectors like mosquitoes, according to Greg Hurst, a symbiont specialist at the University of Liverpool in England.
Daisuke Kageyama, a researcher at the National Agriculture and Food Research Organization in Japan, and one of the study’s authors, expects that more cases like this will be discovered in the future.
The virus was accidentally found by Misato Terao, a research technician at Minami Kyushu University, when she stumbled upon caterpillars feeding on impatiens in the campus greenhouse. She brought them to Yoshinori Shintani, an insect physiologist at the university, who discovered that they were all female moths instead of male moths, which is unusual for this species of caterpillar.
Dr. Shintani bred the female moths from the greenhouse with male tobacco moths and noticed that only female moths were produced in subsequent generations, with rare male occurrences. This led Dr. Shintani and his colleague, Dr. Kageyama, to determine that they had discovered a “male-killer” virus.
Microbial symbionts, such as bacteria, have long been known to affect the reproduction of insects. In this case, the male-killing effect is caused by a virus named SlMKV discovered by Dr. Shintani’s team. Antibiotics did not eliminate the effect, indicating that bacteria were not responsible. Further experiments confirmed that the virus was infectious and inheritable.
The researchers also found that the virus’s effect is reduced and eventually neutralized at higher temperatures. This suggests that the balmy climate in the caterpillar’s native range suppresses the male-killing effect. The discovery of the virus’s vulnerability to heat could have implications for controlling other agricultural pests related to the tobacco cutworm.
Experts believe that viral male-killers may be more common than previously thought. Understanding these mechanisms can contribute to the development of a “female-killer” for controlling invasive pests and disease-carrying species like mosquitoes.
The discovery of this virus aids in the search for ways to control pests, but time is running out to learn from temperature-sensitive microbes due to climate change, according to Anne Duplouy, an evolutionary biologist at the University of Helsinki.