How Humans Are Messing Up Bee Sex

From pesticides to land development to electromagnetic pollution, humans often harm the ability of honeybees to reproduce.

Fly fast and die young: That’s a male honeybee’s lot in life. With less than a one percent chance of successful reproduction, and a 100 percent chance of dying after mating, male honeybees have it tough.

But recent evidence suggests that human activity—including land development, electromagnetic pollution, and use of neonicotinoid pesticides—is making it even harder for honeybees to reproduce, to the peril of the species.

Every spring these males, also known as drones, fly out to congregation areas, mid-air ballrooms where thousands of young bees gather from miles around to show their stuff.

Each seeks to mate with a virgin queen, a week-old female destined from birth to found her own hive. During these females' "nuptial flights" at these events, the queens gather the genetic material they’ll use to inseminate eggs for the rest of their lives. Queens can lay 2,000 eggs on a good day.

Each queen will mate with about twelve of her suitors, fewer than one percent of the males in attendance. Eager males hurtle through the sky behind a virgin queen like a comet’s trail, jockeying for position.

When a lucky drone reaches one of the queens, he mounts her and flexes his abs to extend his endophallus, the bee equivalent of a penis, into the queen’s sting chamber. He releases his semen with such speed and force that there’s said to be an audible pop.

This is the climax of a male’s life—and it’s rapidly downhill from there. The drone’s endophallus stays behind with the queen, and he falls to the ground paralyzed to await his end.

“Probably not such a great death,” says Geoff Williams, an entomologist at Auburn University and an expert on honeybee reproduction. “But hopefully he’s passed on his genes.” (Related: What happens if honeybees disappear?)

The surviving bachelors buzz from one congregation area to another until they die at about six weeks of age—or until the arrival of fall, when resources grow scarce and worker bees decide to permanently evict their deadweight brothers. Drone corpses litter the ground outside the hive.

Pesticide Problems

Now, agricultural pesticides could be making this seemingly bleak life even more difficult. In 2016, Williams and his team published a study in the journal Proceedings of the Royal Society B showing that neonicotinoids, the world’s most common class of agricultural pesticide, may act as a bee contraceptive. Drones exposed to field-realistic concentrations of neonicotinoids produced 39 percent less living sperm—and more often deliver “dead sperm” to virgin queens, Williams says.

During her nuptial flights, the honeybee queen accumulates sperm in a special chamber in her abdomen called the spermatheca. She’ll use that genetic material throughout her life to produce workers—fertilized eggs develop into females, while unfertilized eggs become drones. Too little healthy sperm can throw off the sex ratio of the queen’s offspring and leave the colony short of workers, weakening the hive.

<p>This male&nbsp;<i>Andrena perplexa</i>&nbsp;was caught in Maryland on May 16.</p>

This male Andrena perplexa was caught in Maryland on May 16.

Photograph by Sam Droege, USGS

Bayer, the top producer of neonicotiniods, maintains that the pesticides pose no threat to honeybees when applied to crops properly, says Utz Klages, the company's head of external communications.

But curiously, a field study funded by Bayer and another leading pesticide manufacturer concluded that neonicotinoids do appear to have “negative effects on the interannual reproductive potential of both wild and managed bees,” though the effect differed by country.

The authors of the study, published last year in Science, determined that exposure to these chemicals “reduces overwintering success and colony reproduction in both honeybees and wild bees,” confirming that neonicotinoid pesticides “negatively affect pollinator health under realistic agricultural conditions.”

Use of neonicotinoids has been curtailed in some places: The European Union implemented a full ban on three of these chemicals in early 2018, and Canada is working to phase them out.

Replacements for these pesticides could pose problems as well. A study published last month in Nature found that bumblebee colonies exposed to sulfoxaflor, the pesticide likely to replace neonicotinoids, produced on average 54 percent fewer reproductive bees. That, of course, "means there are fewer bees in the next generation,” says Harry Siviter, one of the architects of the study at the Royal Holloway University of London, and the chemical could affect honeybees in a similar way.

Good Flowers Are Hard to Find

To survive long enough to even have a shot at mating, drones rely on "pollen room service" from their tireless sisters.

“Bees, like us, require diverse diets to be healthy,” explains Christina Grozinger of Pennsylvania State University. But between industrial cornfields and sprawling urban landscapes, a good flower can be hard to find.

“It’s the loss of flowering plants, in terms of both abundance and diversity, that’s reducing the nutritional resources that honeybees and other bees can use,” Grozinger said.

Honeybee hives with unfarmed grasslands in their backyard—think flowering meadows—fare much better than hives surrounded by corn or soybean farms, according to a recent study conducted by the U.S. Geological Service.

After examining 864 honeybee colonies in the Great Plains, the federal scientists determined that hives in the best areas had bigger summer baby booms—on average producing 2,000 to 4,000 more offspring than hives in the worst neighborhoods.

Beyond shrinking the overall dating pool, bad nutrition means each individual drone has less game. Unhealthy bees are more susceptible to viruses and parasites—such as the infamous Varroa mite—and aren’t as physically fit. A poor diet can make for a generation of shrimpy, sluggish drones with no chance of mating.

And a virgin queen with fewer mates means a less genetically diverse hive—which decreases her family’s resilience to disease and environmental stressors.

A Back-End Backup Compass

Scientists aren’t certain how bees only a few weeks old find their way to the same congregation areas used for generations by their ancestors.

One theory is that congregation areas arise in places “where the horizon opens up,” Williams explains, “where you have this intense light.” Other scientists point to proximity to water or landmarks in treelines as determinants of congregation areas.

But what about drones that travel from miles away, where distant treelines and open skies aren’t visible? Honeybees may be using a “backup compass” in their rear ends.

The honeybee’s abdomen boasts a pocket of magnetite crystals—particles of iron that can detect changes in electromagnetic fields, like the one generated by the Earth. Studies since the 1970s have demonstrated that honeybees can use magnetic fields to orient themselves in space, and more recent experiments link electric fields to everything from flower selection to navigation rituals like the famous waggle dance. So it might be that honeybees are attracted to a special electromagnetic signature in congregation areas.

Most human technologies that emit electromagnetic fields aren’t even a blip on a honeybee’s radar—it seems they’re too weak to detect—but entomologist Sebastian Shepherd worries that power lines may be the exception to the rule.

Shepherd and a team at the University of Southampton conducted early-stage experiments examining the possible effect of power lines on honeybee learning, memory, and movement. The results, published this summer in Scientific Reports, are worrisome. Honeybees exposed to low frequency electromagnetic fields like those emitted by power lines were less effective foragers and flew more erratically.

Though Shepherd cautions that these findings are far from conclusive, they indicate that electromagnetic pollution from humans could make it harder for bees leaving the hive. That’s bad news for workers trying to feed hungry brothers and drones in search of congregation areas.

A bee bachelor’s life may seem tragic, but the males of this famously matriarchal species are vital to the hive’s survival.

The queen looms large in our study of honeybees—so much so that male honeybees are scientifically the “neglected sex,” Williams points out. Entomologists are increasingly looking to drones to help explain the impacts of various environmental stressors on honeybee colonies.

Though he may not hold on to his endophallus, the drone may hold the secrets to saving the honeybee. It would also help, of course, if humans could be better wingmen.

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