Male Honey Bees Temporarily Blind Queens With Their Semen so They Can't Mate Again

The semen of male honey bees contains a poison that makes queens temporarily lose their sight after sex, in what scientists described as a "sexual arms race."

In most social insects—the category encompassing creatures like ants, bees, and wasps—the queen mates for one day in her life. But the honey bee queen is different. During an early period of her life, she flies around mating with males to collect a lifetime's worth of sperm.

Even after a number of drones have inseminated her, she might set off again for several days. Scientists think the queen takes the risk of finding more mates because of the long-term gain of having a workforce with genetically diverse offspring, which can help to protect against disease.

This, however, is bad news for males who have already mated with the queen. By buzzing about in search of news mates, she lowers their chances of her offspring carrying their genes.

"This results in sexual conflict between males and queens over the number of mating flights," the authors explained in a digest accompanying their work in the journal eLife. They described this process as a "sexual arms race."

To try to stop the queen from mating with other males, bees use their semen to weaken her sight, the authors believe. The seminal fluid contains toxic proteins which affect the expression of her genes related to vision. These appear to cause the queen's eyesight to suffer for 24 to 48 hours after insemination.

Researchers gave one group of queens seminal fluid, while their sister queens were given a saline solution. They attached tags on the queens to document if and when they flew back to their hives. The team found the queens dosed with semen flew two days earlier than their counterparts, and were more likely to get lost and not return.

To examine their vision, the scientists showed queens a flickering light and measured their brains using electrodes. The queens given semen were less responsive to light than those given saline. The authors also sequenced the queens' RNA, which carries the instructions of DNA, to look for changes in gene expression.

Boris Baer, a professor of entomology at the University of California Riverside and senior author of the study, explained in a statement: "The male bees want to ensure their genes are among those that get passed on by discouraging the queen from mating with additional males."

"She can't fly if she can't see properly."

The research builds on previous work by Baer and his team looking at how proteins in bee semen could affect the behavior of queens. "We found at least 300 of these 'James Bonds,' little secret agents with specific missions," he said. These included proteins that target the sperm of rival males.

Baer said the queen's eyesight likely returns as most fly when they are older to set up new colonies.

The findings further our understanding of bee populations, which are declining. Between 2016 and 2017, for instance, U.S. beekeepers lost 33 percent of their honey bee populations.

"More than a third of what we eat depends on bee pollination, and we've taken bees' services for granted for a very long time," Baer said. "However, bees have experienced massive die-offs in the last two decades. Anything we can do to help improve their numbers will benefit humans, too."

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Scientists believe male honeybees blind queens during sex. In this stock picture, two bumblebees are pictured on a honeycomb. Getty