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An RNA-enriched sugar syrup is poured into a beehive as part of the trial for a new varroa mite treatment that could pave the way for an agricultural revolution when it comes to treating for pests.
Peter Essick

After more than a decade in the industry, commercial beekeeper Liana Teigen Moreno thought she knew what she was doing when it came to making honey. A hipster pixie with a platinum crew cut and bright blue eyes, Teigen tends to 800 beehives in northern Florida. Her experience at the University of Florida’s Honey Bee Research Lab in Gainesville taught her everything she needed to know about bee diseases, knowledge that came in handy late last year when she realized that an insidious parasite that she had first learned about working her way through college as a part-time beekeeper had decimated her hives—despite her best efforts. “I wasn’t quite thinking that I was immune, but I’d gotten a little cocky,” she confesses.

She is not alone. American beekeepers lost nearly half their managed bee colonies this year, according to an annual bee survey released by the nonprofit research group Bee Informed Partnership on June 22. It’s a staggering blow for an industry that not only provides honey, but vital pollination services for nearly a third of the fruits and vegetables Americans eat, from blueberries to strawberries, peaches, melons and cucumbers.

When it comes to agricultural animals, domesticated bees are as important to the U.S. food supply as cows, chickens and pigs, yet the losses continue to climb. This year’s 48% annual loss, covering the 2022-2023 winter season, is up from 2021-2022’s 39%, and nearly on par with 2020-2021’s 50.8% mortality rate—the worst since the survey started in 2008. Climate change, pesticide-laden crops, and declining wild plant biodiversity all play a role in honeybee colony death, but the biggest threat is the varroa destructor, an invasive, parasitic mite smaller than a pin head that nonetheless extracts a big toll from the bees it feeds upon. Varroa mites have plagued beekeepers ever since arriving in the U.S. from Asian honeybees in the mid 1980s, but in recent years, commercially available treatments have lost their efficiency, even as the mite’s viral load increases. “Varroa mites are the number one threat,” says Teigen. “It’s something that beekeepers have been struggling to control for years, and to be honest, it’s starting to feel a bit like a losing battle. Really what we need to turn the tide is more tools in our tool belt.”

Read more: The Bee Whisperers of Slovenia Have a Plan to Save Colonies From Climate Change

A new tool is in the pipeline: Boston-based biotechnology company Greenlight Biosciences has developed an anti-mite RNA treatment for beehives that uses a similar technology to Pfizer’s breakout COVID-19 vaccine. Only in this case the RNA is used to suppress a protein vital to the reproductive system of the varroa mite, instead of creating a dummy protein designed to prime the human immune response. If DNA is the blueprint at the core of cell development in every species on earth, RNA is the cement mixer creating custom protein building blocks. Each RNA formula is so specifically tailored that it only works on one target—a precision strike compared to a wide-spectrum pesticide’s fire-bombing, which can cause collateral damage in other, beneficial, insects.

Still in its infancy, this RNA-based technology heralds a new revolution in preventing disease and staving off pests across the agricultural spectrum, from the botrytis that beards blueberries and grapes with fuzzy gray mold to the Colorado potato beetle and maize-munching fall armyworm that are devastating crops from North America to southern Africa, and even the spider mites that suck sap from common houseplants. RNA manipulation has the potential to become a powerful new tool in the treatment of some of agriculture’s most pernicious pests, says Andrey Zarur, who co-founded Greenlight Biosciences in 2009, with the goal of finding biological solutions to the overuse of chemicals as pesticides, herbicides, and fungicides in the world’s food system. “RNA will be as revolutionary to our food supply as it has already been to human health through the COVID vaccines.”

Unlike their wild pollinator cousins, honeybees are in no danger of going extinct. When a beekeeper like Teigen loses half her colonies, she builds new ones by splitting what remains and restocking them with young queens, who will go on to lay thousands of eggs for their new hives. But the process is time consuming and labor intensive, and it means decline in honey production as well as pollination services. When beekeeper Barry Hart launched his honey business in Fargo, Ga., in 1986, a 10% loss would have been considered catastrophic. These days he is happy if he can keep it below 40%, and hive splitting is an essential part of his annual workload, slotted between pollination gigs and honey production. “Used to be, the only thing I ever worried about was black bears,” he says, in a southern Georgia drawl. “Now it’s mites I can’t even see without my readers.”

Modern agriculture would not exist without modern beekeeping. Of the 100 crops that account for 90% of the world’s food supply, 71 rely on bee pollination, according to the Food and Agriculture Organization. Take California’s $5 billion almond crop for example. For six weeks, starting every February, 1.35 million acres of almond trees burst into bloom. Like avocado, apple, and peach trees, their pollen is too heavy to be carried by the wind, and so they must be pollinated by insects in order to produce nuts. But decades of industrial monocropping, combined with heavy pesticide use to keep those commodity crops healthy, have decimated native pollinators. To get the job done, beekeepers from all corners of the United States haul their hives—some 1.2 million—to California’s central valley by the semi load.

Beekeepers earn about $200 a hive for their effort, more than they would ever make producing honey, but it comes with a cost. Billions of bees buzzing around one small area are a pathogen playground. “It’s like a cesspool,” says Hart, who nonetheless goes every year. “Every beekeeper from the bottom of the ladder to the top is there. You have no idea who your bees are sitting next to, what kind of viruses they have, and whether they have mites.”

Read more: Beekeepers Working Harder Than Ever As Nearly Half of U.S. Honeybee Colonies Died Last Year

After layovers in North Dakota for alfalfa pollination and Florida for oranges, among other crops, Hart brings his bees back to Georgia to harvest their honey and prepare for winter. By then the mite population, acquired in California’s almond orchards, has grown exponentially. The varroa mite is not a tick, but it acts like one, hopping from one foraging bee to another, sinking its barbed tongue into the torso and feeding on haemolymph, the insectile equivalent of blood. On a human scale, says Teigen, it would be like having a tick the size of a sewer rat sucking from your gut.

On a fully grown bee, an adult varroa is a nuisance and a viral vector. In the hive’s wax-walled brood cells, where nurse bees tend to the next generation, it is a population bomb. Varroa mites reproduce when a pregnant mite, hitchhiking into the hive on the torso of an adult bee, sneaks into a brood cell hosting a larval bee. Worker bees stuff the cell with brood food, a combination of honey and protein-rich pollen designed to nurture the developing pupa, and cap it with wax until the bee is ready to emerge. Meanwhile, the female varroa mite gets to work, depositing her offspring in the cell and feeding on the developing bee larva. The mite’s children mate, and by the time the fully grown bee is ready to emerge from her cell, she is both weakened from nutrient loss and carrying a new cohort of pregnant varroa mites ready to “spread the good news,” deadpans Teigen. “As elegant and beautiful as a honeybee colony is, varroa mites come in and weaponize it. As beekeepers, we want to be raising bees, but we end up raising mites as well.”

Beekeeper and researcher Liana Teigen uses a smoker to calm bees before looking for their queen. Her work is part of an ongoing trial for Greenlight Biosciences, a biotech startup that uses RNA technology to treat for common agricultural pests. (Peter Essick)
Beekeeper and researcher Liana Teigen uses a smoker to calm bees before looking for their queen. Her work is part of an ongoing trial for Greenlight Biosciences, a biotech startup that uses RNA technology to treat for common agricultural pests.
Peter Essick

Many of the young bees emerge unable to fly, afflicted with deformed wings, carrying viruses, and so depleted that they cannot fulfill their primary function of tending to the next generation of young broods. In this way, a healthy-seeming hive can collapse over the course of just a few weeks. Beekeepers have access to multiple products designed to combat mites in beehives, from vaporized forms of formic and oxalic acids that must be applied while wearing protective equipment, to potent insecticides and miticides that render any resulting honey unsellable due to their toxic residues. The problem is that both kinds of treatments harm bees, and increasingly they are becoming less effective against mites. When Teigen saw the mite devastation in her own hives despite previous applications of her usual treatments, she overreacted, trying a different formulation that ended up killing as many bees as it saved. “Treating my bees is a necessary evil,” she says. “But a lot of times I feel like I’m crossing my fingers and hoping that it isn’t too strong or that the queen won’t accidentally get killed in the process.”

Hart, who used to treat his bees twice a year for mites, now has to increase the frequency, throwing his tight pollination schedule off and further reducing his honey yields. “It’s gotten to the point where if we’re gonna stay in business, we’re gonna have to do something else, because mites are getting harder and harder to kill,” he says.

That something else looks like nothing Hart had ever seen before, at least not before Greenlight approached him with an offer to trial their new mite treatment on some of his colonies. Instead of a spray or a vapor, the Greenlight version, which doesn’t have a commercial name yet as it is still in regulatory review at the Environmental Protection Agency, looks like a white, padded mailer filled with syrup. One side is perforated, and when it is placed inside of a hive, the RNA-laden sugar solution drips down into the honeycomb, where nurse bees take it up to feed their brood—dousing any mites that happen to be hiding in the cells in the process. Because the RNA is designed to suppress only one protein essential for varroa mite development, it has no impact on the bees.

If the varroa mite weaponizes the elegance of bee reproduction for its own procreative ends, Greenlight’s RNA solution weaponizes that weaponization by stopping the reproductive cycle in its tracks. “If they can come up with good evidence that it’s working, that it doesn’t have side effects, and that it’s effective in the field at low cost to the beekeeper, that’s exactly what beekeepers need,” says Nathalie Steinhauer, science coordinator for the Bee Informed Partnership, which runs the annual colony-loss survey. “If anything, it’s good to have a new [option], so that we don’t have to rely as much on the few existing treatments that are already gathering resistance in the varroa mites.”

Eli Powell, a microbiologist at the University of Texas, Austin’s Nancy A. Moran Research and Lab Group, which focuses on insect and bacterial genomics, calls Greenlight’s RNA solution “positive. We need new ideas in order to combat a lot of these problems that bees are facing.” At the Moran Lab, he and his colleagues have developed an RNA solution that tackles another bee pathogen called nosema. His team has genetically modified bee gut bacteria to produce anti-nosema RNA within the bee’s digestive system, a different delivery mechanism that shares the same base RNA technology. “I don’t see anything but growth in terms of using these types of approaches,” he says.

When Hart first tried the treatment as part of a Greenlight trial two years ago, he had his doubts. How could something that wasn’t even designed to kill mites work? But the contraceptive effect soon became evident. Within a few weeks he could tell just by lifting a lid which beehives had been treated, and which had received a placebo. “Because at the end of the trial, most of those would be dead. The others will be full of happy healthy bees.”

Teigen is now in the process of testing the Greenlight miticide on nucs—mini colonies designed to breed queens—to make sure it has no adverse impact. A queen will mate with dozens of drones on her maiden flight, collecting spermatozoa before returning to her hive for a lifetime of egg-laying. If she mates well, she will have enough sperm to last a few years. But if she runs out, or doesn’t mate at all, her hive will turn against her. It is essential to ensure that the Greenlight treatment doesn’t impact her flight, or her subsequent ability to lay eggs. After Teigen’s bad experience overtreating her bees last year with a common chemical miticide, she is eager to see a product on the market that does the job without hurting her beloved bees. “Putting an insecticide in a box of bugs to kill one bug, but not the other bug, has always felt very counter intuitive,” she says. “Having something with a much lower stake would be life changing, for me and my bees.” (While the RNA treatment has no impact on the bee’s honey, neither Hart nor Teigen will sell any of the honey produced by bees in the trial, nor will they harvest honey produced during a treatment.)

Greenlight is in the final stages of regulatory approval for its first RNA solution, designed to combat the potato beetle, but its varroa mite treatment is still months away. The company submitted the solution for regulatory review at the EPA in February, and the process can take up to two years. But the elegant aspect of RNA-based treatments is their versatility. Now that the company understands the varroa mite system down to the individual protein level, it doesn’t take much to switch the formulation to target other varroa proteins. Or even other mites for that matter. Which could come in handy. Another invasive mite, called Tropilaelaps, is already wreaking havoc among Asian and European hives, and has recently been spotted on U.S. soil. It reproduces at an even faster rate. At least until it meets a fragment of RNA with its name on it.

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