Stopping the Next Great Honeybee Killer—Before it Reaches the U.S.
One day soon, parasitic mites could accidentally arrive in North America. It's a doomsday scenario for pollinators that scientists are racing to avoid.
Sammy Ramsey has glimpsed the future of honeybees, and it’s terrifying: collapsed colonies, crumpled wings, deformed legs, and a villain that eats babies alive.
“Think of the movie Alien with Sigourney Weaver,” he says, referring to the hit 1979 sci-fi horror film. “There is this really creepy thing the alien does where it gets close to someone’s face, and then another mouth comes out of its mouth.”
Tropilaelaps mites, or tropi mites, have similar mouth-within-a-mouth jaws, says Ramsey, an entomologist at the University of Colorado Boulder and a National Geographic Explorer. The tiny parasites of honeybees also have a clever modus operandi: A pregnant mite gets herself sealed into a honeycomb cell with a helpless developing bee. There, she and her offspring can feed off the “squishy bag of nutrients” undisturbed.
Ramsey first encountered the mites in Thailand in 2017. When he opened his first infected hive and witnessed the destruction they wreaked, his stomach dropped. “They go after the most vulnerable members of the colony,” he says. To make matters worse, nurse bees rip wax off cell caps in a frenzied craze searching for the intruders, unwittingly exposing the colony's defenseless brood of developing young to the elements.
If the trail of destruction tropilaelaps has left in colonies across Asia, the Middle East, and more recently in eastern Europe, is anything to go by, it could sound the death knell for the Western honeybee (Apis mellifera)—North America’s most common bee species and its most important pollinator, responsible for a third of all crops. Entomologists fear it’s only a matter of time before the mite reaches Western Europe and makes a beeline across the Atlantic.
To make matters worse, many mysteries surround tropilaelaps, despite being known to science for decades. “We don’t have a good understanding of their life cycle, what allows them to spread, how they move between locations, or how to kill them,” says Ramsey. If the mites showed up on U.S. soil tomorrow, we would be “in the dark,” he adds, and beekeepers would have very few tools to defend against them. “It’s the scariest thing to my mind,” he says.
But Ramsey has a plan to arm beekeepers against the scourge, and he believes the key to saving the species could be found on a small volcanic island called Jeju off the coast of South Korea.
On a recent August morning, the sun has just risen over Jeju, dubbed the Hawaii of Korea, and the ever-energetic Ramsey is striding through a small tangerine orchard to a clearing where a line of Styrofoam bee boxes sit on the dewy grass. He and local beekeeper In-jun Son, who’s helped procure the honeybees for this particular experiment, smoke the hives to calm the insects, and Ramsey opens a box, retrieving a frame at random. He gently brushes off some straggling bees, then takes it over to his makeshift lab—camping tables and chairs under a towering cypress tree—unzips his trusty bee suit, and settles down to work.
Serenaded by a symphony of cicadas, Ramsey uses a pair of forceps to delicately remove the wax capping on a hexagonal cell—one of the thousands that fill the wooden frame and act as nurseries—and pulls out a half-developed baby bee. At this stage, merely a few days old, the pale-looking pupa is but a ghostly imprint of its handsome future self. Ramsey holds it up to his magnifying loupes and spots two critters: A lighter, more translucent tropilaelaps zipping frenetically up and down the bee’s body, and a dark-hued varroa destructor mite, sucking lazily on its sumptuous meal.
For decades, the varroa destructor mite has been public enemy number one of U.S. beekeepers, infesting nearly every beehive across the country since it arrived in Florida from Southeast Asia in 1987. Along with stress from climate change, habitat loss, and pesticide poisoning, the mite is the primary driver of honeybee deaths. “Beekeepers have been experiencing pretty high losses for 15, almost 20, years now,” with a third of their colonies dying out annually, says Geoff Williams, director of Auburn University’s Bee Center in Alabama, who helps coordinate the annual U.S. Beekeeping Survey.
The declines are a major threat to agriculture. In the U.S., honeybees pollinate $15 billion worth of crops every year—from almonds to apples to alfalfa for cattle. Varroa has been linked to the majority of colony collapses, causing a historic $600 million in 2024 crop losses. And that doesn’t account for the invaluable role that the insects also play in sustaining ecosystems, pollinating many fruits, seeds, and berries that birds and small mammals eat.
The damage from varroa has made entomologists especially wary of honeybee parasites like it. “We can’t afford another parasite to come in and create another bundle of issues for our bees,” says Ramsey.
The pollinators themselves are one reason the threat is so great. There are over 20,000 bee species in the world, but the Western honeybee is “the workhorse for pollination and the production of natural products like beeswax and honey,” says Williams. Keepers favor these bees over other species because they’re relatively docile, live in large colonies capable of producing vast amounts of honey, and thrive in portable hive boxes that can be trucked wherever needed.
But western honeybees are especially vulnerable to “foreign” parasites and diseases from the east. That’s because they’re the only honeybee species, out of more than seven, to have evolved in northern Europe, rather than Asia. Like varroa, tropilaelaps hail from Southeast Asia, where many beekeepers rely on the native Asian honeybee (Apis cerana). So far, the eastern species has escaped tropilaelaps. However, those that do keep the western species to pollinate certain crops have suffered losses—sparking concerns of another tinderbox situation should they reach U.S. shores.
“If tropilaelaps gets to North America, the devastation it will cause would be just terrible,” says entomologist Maggie Gill, co-lead of the Tropilaelaps Mite Task Force at COLOSS, an international non-profit focused on honeybee health.
Already, there’s been a near miss: In January 2025, authorities intercepted a container vessel bound for New Jersey from South Asia after its crew reported a swarm of giant honeybees aboard. Testing later revealed that the bees were carrying 28 tropilaelaps mites—the first time the critters have been detected on inbound cargo.
“The case showed us how vulnerable we are,” says Danielle Downey, director of the Utah-based nonprofit beekeeping research organization Project Apis m. Although the U.S. has strict import regulations—allowing in only adult bees from two tropilaelaps-free nations, Canada and New Zealand—the mites could arrive on bees that stow away on ships or are illegally smuggled in.
Once it sneaks in, tropilaelaps could do even more damage than varroa because on many counts, it’s a more formidable foe, says Gill. The mites’ translucent color and smaller size (just three-quarters of a millimeter) make them harder to spot. They also reproduce much quicker. Estimates suggest that they lay eggs every 24 hours (instead of 30), and mature in seven days or less (rather than 10). “So the number of mites that you get within a colony is just exponentially bigger than varroa,” says Gill.
Both mites carry viruses that can infect honeybees, but the “angry” feeding style of tropilaelaps results in more physical damage to the bees, including to their immune systems, notes Ramsey. It’s a double whammy that makes the pollinators more vulnerable to the hitchhiking viruses. And because the hive is such a compact space, infections can spread like wildfire. The most common diseases result in deformed wings, paralysis, and the death of queen bees. With little intervention, the colony quickly collapses. “Varroa is damaging, but tropilaelaps is just more so,” says Gill.
And then there’s the quadruple whammy: The possibility that both mites could reproduce in the same hive cell, at the same time. This is why when Ramsey sees the two mites together nibbling on the same bee on Jeju, he exclaims enthusiastically to his two graduate students, who sit nearby working on their own hive frames: “This cell has tropi and varroa, and they’re both reproducing!”
He explains the significance of this to me over a watermelon juice break later that morning, several frames—and similar observations—later: “Plenty of people have seen co-infestation, but there’s always been a question of whether they can reproduce on the same resource, which is why we were so excited.” Rather than keeping each other in check through competition, it appears the two can coexist and breed undeterred. A dual infection on a single bee almost always means weakened immune systems, more viruses, and higher mortality.
The find is an interesting wrinkle, but there’s more to come. The work they’re doing will provide a baseline count of mite infections that he and his team have to do before they test bigger questions. Chief among them: If tropilaelaps makes it to U.S. soil, just how bad will the damage be?
Initially, experts believed that since “it’s a tropical mite,” the incursion would be limited to the warmer states, says Gill. That’s because, unlike varroa, tropilaelaps feeds solely on a colony’s developing young. And egg-laying halts when temperatures drop. In Southeast Asia, the weather allows bees to reproduce year-round. So, the hope was that winter might stall the spread in temperate regions and that colder climates might escape the tropical parasites entirely.
But with reports of tropilaelaps surfacing in notoriously cold places, such as Russia, Kazakhstan, and Georgia, they’ve had to revise their thinking. “Nobody expected it to be able to survive in these conditions, but it does,” says Gill, who collaborates closely with researchers in Georgia to study the mite.
The mites’ winter behavior in these areas is also puzzling. “The mites disappear somewhere for about two months and then reappear,” says Anna Brandorf, a bee researcher at Russia’s Rudnitsky Federal Agricultural Research Center of the North-East who has tracked tropilaelaps in both Kazakhstan and Russia. “We have no idea where they go and why they go.”
This mystery is a key reason why Ramsey and his team have come to Korea: “It’s the first region outside Southeast Asia where these mites became established,” explains Ramsey, who has primarily studied the mites in other tropical countries like Bangladesh and the Philippines. “Plus, Jeju has a winter,” he says. Which means any useful findings from their summer-to-spring experiment will be applicable to temperate countries, including the U.S.
It’s the crack of dawn the next day, and Ramsey is explaining his hypotheses to me: “Maybe the mites are going into the soil. Or maybe they’re in the colony, and people just don’t realize that they’re wedging themselves between little nooks and crannies to overwinter.” They might even be riding out the season on alternative hosts like rats—the animals the mites were living on when scientists first discovered them in 1961.
As we chat, we watch his graduate students, Carmen Black and Treson Thompson, weave their way through the grass clearing, retrieving the 10 rodent traps they had set the night before at varying distances from the hives. The pair check the oblong, aluminum boxes: all are empty, save for one.
The unwitting visitor, who’s gorged on part of a peanut butter sandwich, is a tiny harvest mouse. Holding it by the scruff of its neck, Black gently combs through its fur—first with a hand comb, then a pair of forceps, and finally a blunt scalpel—before swabbing its ears with a Q-Tip. She works fast, wrapping up the inquisition by giving the mouse a soothing shampoo bath and quick towel dry, followed by a brief observation period in a recovery cage.
This particular rodent is tropilaelaps-free, but perhaps some others—at this or the team’s other two test sites elsewhere on Hallasan, Jeju’s highest peak—might yield some mites as trapping continues in the coming months.
The team will also periodically sample soil around the hives, trap flying bees, and set up trapdoors “moat-style” to figure out if the mites are leaving in another manner, such as “physically walking out from the hives or flying out on bees,” says Black.
These investigations may also shed light on how tropilaelaps spreads from one colony to another. In Georgia, for instance, Gill and her collaborators have observed mites hitchhiking on adult bees as they leave with the queen to establish a new hive. Since my visit, Ramsey’s team has spotted some mites hitching rides on worker bees departing colonies. The mites don’t typically feed on adult bees, but perhaps they make an exception for transit.
It’s one of the biggest concerns for beekeepers on the ground, including Bang-cheol Kang, president of the Korea Beekeeping Association’s Jeju branch. The island has seen unprecedented winter bee colony losses since 2022, though it’s hard to link those directly to tropi mites, says Black. When Ramsey visited Kang’s bee farm later that day to help assess his hives for tropilaelaps damage, his team found one site with a serious infestation, while the other was largely in the clear. The veteran beekeeper of 20 years posed two questions: “How do the mites move from one colony to the next?” and “How far can the bees fly with the mite?”
Not having answers is “disappointing,” says Thompson: "But we're filling in a lot of blanks about tropi's strengths and potential weaknesses."
(Nature’s vital pollinators are smarter than we ever imagined.)
Filling in those blanks could give beekeepers on Jeju and elsewhere a way to fight back—perhaps even a cure. Classic varroa treatments, including the chemical pesticide amitraz and its eco-friendly, organic acid alternatives, don’t translate well because they can’t penetrate the wax caps on hive cells, where tropilaelaps typically spend most of their lives.
Formic acid, a naturally occurring compound found in ant venom, does. Ramsey’s team is trialing a low-cost version of this in Jeju: thin wooden strips soaked in liquid acid. When slotted under the frames, vapors will sublimate throughout the hive, killing the mites.
Finding the right concentration, however, is a fine balance, warns Victoria Soroker, an entomologist at Israel’s Agricultural Research Organization. Too low, and the treatment is ineffective. Too high, and the bees die. “Things that usually harm mites can also damage bees,” she explains.
That’s why Ramsey’s team is assessing both mite survival and honeybee health. Additionally, they’re testing two other treatments: a novel, non-toxic product that’s misted onto frames; and a thermal therapy that involves placing infected frames in a specially heated box.
Some pesticides don’t just harm the bees but also contaminate the honey that they produce. So elsewhere in Asia, entomologists are experimenting with other options, including essential oils. Jung, for instance, is exploring extracts from tobacco and thyme; while Kitiphong Khongphinitbunjong, a honeybee researcher at Thailand’s Mae Fah Luang University, is studying those from lemongrass and ginger. “We’re trying to find natural products to control tropilaelaps,” he says.
It’s important to cast as wide a net as possible, says Ramsey, noting that the mites might become resistant to treatments, as varroa did. “Rotating between treatment measures is the best way to go,” he says.
Ramsey, however, hopes it won’t come to that. For him, preventing the mites from reaching the U.S. is the best-case scenario. Once the mites gain a foot hold, “it’s over,” he says. “You can pack it in—there are almost no examples where we have been able to successfully eradicate a parasite after that point.”
Varroa is a prime example: When the mites reached the U.S., researchers knew little about them, Ramsey says. “They were able to just run rampant before we eventually figured out how to control them.” By then, it was too late—varroa spread to 19 states in under two years, and all 50 within a decade.
“You don’t want to have your enemy at your door before you start to panic,” says Natapot Warrit, an entomologist at Thailand’s Chulalongkorn University and one of Ramsey’s collaborators. “You need to be very proactive about this.”
In other words, prevention is always better than cure. That’s why Ramsey is working so feverishly to learn more about tropilaelaps in South Korea and elsewhere in Asia. In addition to the field tests, he plans to develop a swab test—similar to COVID-19 test strips—that will allow beekeepers to quickly assess their hives for mites without sacrificing any bees. It’ll also do away with tedious visual inspections like the ones he and his team were carrying out in Jeju.
Moreover, Ramsey points out that a network of labs to keep track of pollinator diseases spreading in global bee populations could help avoid outbreaks in the future. "We have a very consistent tendency to think of problems that are happening in other parts of the world as someone else's problems, and to ignore these problems until they arrive,” he says. Instead, he envisions a system that would flag parasites annually similar to how the World Health Organization and national health agencies forecast which flu strains will dominate each year’s flu season.
It’s a tall task, Ramsey admits, “but I am an ambitious human.”
