Mite-y Watchman

In the fight to protect honeybees from parasites, researchers turn to ’shrooms and sperm banks.

September 17, 2015

Photo: Gilles San Martin/FlickrA Varroa destructor mite on a honeybee's head

Varroa destructor. The name sounds like a villain from Transformers, and, sure enough, it’s a nasty enemy—if you’re a honeybee.

This incestuous (more on that soon), bloodsucking mite arrived a quarter-century ago as a stowaway on bees smuggled into the United States. Since then, it has wreaked havoc on hives across much of North America, compounding the threats of pesticides and disease already taking a toll on the pollinators. According to the U.S. Department of Agriculture, honeybee losses in managed colonies, which beekeepers rent out to farmers, hit 42 percent this year. Mite infestations were certainly a factor.

Adult varroa mites live and feed on adult honeybees. “Relative to our body, it’d be like having something the size of a pancake stuck on you,” says Steve Sheppard, an entomologist who runs the bee lab at Washington State University.

Photo: Monika Fischer/Flickr

When one of the sanguivorous beasts is ready to lay eggs, she takes part in an exquisitely timed dance. In the hours before worker bees form a cap over a brood cell—where a single bee transitions from an egg into an adult—the mite drops off the belly of a nurse bee, slips inside the chamber, and nestles in under the larva. Over the next two weeks or so, the invader noshes on the developing bee and lays her eggs: first a male, then up to four females. The young bloodsuckers reach maturity a couple of days before the bee breaks out of its cell. At this point the mite siblings breed with each other several times—cue the romantic music—near the mound of their feces that has piled up within the brood cell. Around two days later, the mom and daughters hitch a ride on the bee as it exits. The lone brother stays behind to face his doom: The nest-cleaning bees come in and kill him, removing his carcass to prepare the cell for the next bee egg.

Meanwhile, the young bee emerges harboring mites and possibly harmful viruses. It may also suffer from stunted wings and malnutrition. Unchecked, a mite infestation can destroy an entire colony within a couple of years. “It is a major problem for beekeepers,” says Sheppard. “Nearly all the safe, easy-to-use-chemical control agents have been used, and now the mites are resistant.”

Gilles San Martin/FlickrPhoto: Gilles San Martin/FlickrA varroa mite on the head of a bee nymph

So Sheppard is on a quest to find new ways to protect the pollinators. You could say working with the insects was his destiny: Sheppard grew up surrounded by apian books and equipment from his great-grandfather, who was an avid beekeeper. That early exposure led him to take a beekeeping course in college, and he was hooked. Sheppard spent decades breeding Western honeybees to better tolerate the varroa mite and its viruses. He built a drone sperm bank to store germplasm from foreign bees that might help their U.S. cousins become more resistant to the parasite and its pathogens. His most recent—and most unconventional—endeavor, however, involves mushrooms.

Last year, Paul Stamets, a mycologist who runs the mushroom company Fungi Perfecti, contacted Sheppard with an unusual idea. Having gathered compelling evidence that fungi from old-growth forests in the Pacific Northwest have strong antiviral properties, he thought the ’shroom approach could help bees, too. (Fungi have an arsenal of antiviral and antibacterial compounds to ward off pathogens; the most famous is penicillin, which Alexander Fleming isolated from the Penicillium rubens mold, a microfungi, in 1929.)

So far, Stamets and Sheppard have found that feeding liquid extracts from some strains of the forest mushrooms lowers the virus load in mite-infected honeybees without hurting the buzzers. Bees that dined on extract-laced sugar water also lived longer than those fed only sugar water.

In addition to feeding bees the extracts, Sheppard and Stamets are also looking into whether the insects can use the ’shrooms to fight off mites from the outside—by covering the furry pollinators with a mushroom-spore risotto of sorts. Fungi Perfecti grew Metarhizium anisopliae, a fungus known to kill varroa mites, in about 10 pounds of cooked brown rice. “It’s really disgusting-looking,” says Sheppard, “like there’s mold growing through rice, and you have to wear a respirator when you handle it.” 

Last week, Sheppard put the icky rice in little screen wire cages within some hives. “The bees will crawl around on it, chew on it, get spores all over their bodies”—and then spread them to the mites. “If it works, it’ll be great,” says Sheppard. “But it won’t fix the problem.” Treating bees with ’shroom spores and extracts would help keep mite numbers low but likely wouldn’t wipe them out entirely. Additional tools would probably be necessary.

Sheppard is also seeing whether high concentrations of carbon dioxide might help kill mites in indoor hives and telling beekeepers to change out their combs more frequently to prevent pesticide buildup. And then there’s that sperm bank.

Photo: Stew and Vee Carrington/FlickrCarniolan honeybees

Since 2008, Sheppard has had a special permit to bring bee sperm from elsewhere into the States (an importation ban has been in effect since 1922). In 2013, his lab launched a germplasm repository where the precious material is cryopreserved. The goal is to build a larger gene pool in the United States, breeding for resistance to mites as well as other factors such as climate. Italian bees, for example, reproduce quickly—a trait that could be useful to provide maximum pollination of early-blooming crops in the South. The genes of the Carniolan bees from the eastern Alps, meanwhile, could provide more resistance to cold weather.

Of course, to store sperm, first you have to collect it. Here’s how it works: In the afternoon, all the males leave the hive and congregate somewhere midair for a few hours, “loitering around, waiting for virgin queens to fly up,” explains Sheppard. Every 20 minutes or so, the drones return to the hive to gobble up some honey and then head back to the posse. That's when the research team simply puts a screen over the hive entrance to catch them.

In nature, a drone will grab onto a queen, squeeze one-third of its blood into into her through his endophallus; then he falls to his death (being a male mite or bee, it seems, guarantees a violent end). To replicate that situation, Sheppard places the drone under a microscope and, armed with a syringe with a dial for suction, squeezes the fellas until they expel about a microliter of semen “the color of coffee with milk.” That tiny amount means the researchers have to catch a lot of drones to build up their germplasm stores. But there’s less pressure these days: Before Sheppard’s team figured out how to freeze the precious stuff, they had only two weeks to get it back to the United States and inject it into queens.

While Sheppard and his colleagues haven’t hit upon a silver bullet—something that’s unlikely, given the dozens of threats facing honeybees—“I think we’re making progress,” he says. From ’shrooms to gassings to new genes, beekeepers need all the ammo they can get.


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