Protecting honeybees from the Varroa destructor mite

May 20, 2021

Today, GreenLight Biosciences announced the acquisition of Bayer’s topical RNA Intellectual Property portfolio that includes bee health capabilities to protect against the Varroa destructor. The novel mite-control approach allows beekeepers to target the parasitic mite without harming surrounding biodiversity, a key advantage over other treatments on the market today.

You can tell the health of a beehive from its buzz. Just ask Barry Hart, who bought his first bees in 1987. Soon after, the Georgia farmer saw a 5 percent annual die-off of his hives. In the past decade, however, Hart experienced up to a 60 percent loss—a troubling trend mirrored in a recent US Department of Agriculture report.

It’s challenging to be a beekeeper these days, with colonies collapsing in the face of habitat destruction and pesticide pollution, but bee farmers also point to another mighty foe: the varroa mite.

Beekeeker Barry Hart checks his hive of honey bees in Barwick, Georgia
Beekeeper Barry Hart checks his hive of honeybees in Barwick, Georgia. In the background is a squash field where the plants are pollinated by the bees.

Resembling a tick, this destructive parasite damages bees at an individual and population level by depleting bees’ fat reserves and carrying viruses that cause—in addition to other illnesses—wing deformation. 

Current pest-management systems struggle to control the increasingly resistant mite while preserving the health of bees and their supporting ecosystem. GreenLight’s solution, an RNA-based approach, targets the varroa mite directly at all stages of its development while keeping the bees, their broods, and the surrounding biodiversity safe. A cousin to the mRNA used in some of the most effective Covid vaccines, GreenLight’s product can be a more sustainable alternative to traditional chemical pesticides, protecting pollinators and plant life.

Originally associated with the Asian honeybee, the Varroa destructor spread throughout Europe when Russian beekeepers introduced the higher-yield European honey bee to Asia in the middle of the 20th century. Spreading westward, the small arachnid reached the United States in the 1980s and today, USDA figures show that about 40 percent of US hives have been affected, with a level of mites high enough to cause significant bee mortality.

Honey Bee with parasitic Varroa Mite attached being held by Beekeeper Barry Hart, Barwick, Georgia.
Honeybee with parasitic Varroa mite attached being held by beekeeper Barry Hart in Barwick, Georgia.

When a queen bee lays a new egg, it is placed in a hexagonal cell in the honeycomb. After three days or so, the egg hatches into larva, where worker bees feed it hundreds of times a day; five or six days later, the larva enters the pupal stage, where it transforms into the adult bee. When the larva pupates, the worker bees cap its cell with wax, sealing it off from the rest of the hive.

The female varroa mite, carried by a worker bee, enters the cell to lay its eggs in the hive at a crucial juncture: just before the bee larva pupates and the cells are sealed. By the time the adult bee emerges, the mite larvae have already hatched and attached themselves to the bee. Fully grown on a bee, the mite resembles a tick on the bee’s abdomen, equivalent in relative size to a human’s fist held to the chest. 

The mite population in the hive increases exponentially, doubling every few weeks while consuming the bees’ fatty tissues, thus lowering their body weight. Affected bees take longer to return to the hive, perhaps because they are unable to navigate well or fly far due to their weakened state and the additional burden of carrying the mite. 

James Masucci, a Missouri research scientist and beekeeper who works at GreenLight, says that although the mites themselves may not kill the bees, they weaken immune systems and transmit  viruses—most notably deformed wing virus—that eventually destroy the bee colonies.

Although honeybees are susceptible to other parasites, climate stress, starvation, and pesticides such as neonicotinoids, Masucci is confident that the varroa mite is the chief culprit. “We consider mites to be 70 to 80 percent of the cause of decline in colony health,” he says.

As US farmers shift to crops like soybeans, which do not provide bees with much sustenance, it has become harder for colonies to survive “although beekeepers have been dealing with that since before the mites,” Masucci says. By around 2000, varroa mites became widespread and a few years later, colonies started dying in large numbers, a correlation confirmed by the USDA.

Why varroa mites are tough 

There are several pesticides now used against varroa. Three synthetic chemicals—coumaphos, fluvalinate, and amitraz—are put on plastic strips and hung outside the hive, where bees come into contact with them. Organic treatments, meanwhile, include formic acid, oxalic acid, thymol, and beta acids.

Fluvalinate and coumaphos have been used so much that the mites have started showing resistance: “If they develop resistance to amitraz,” says Masucci, “the US industry is in big trouble.” Meanwhile, the organic treatments mostly act as fumigants: The beekeeper takes a lump of the material and places it in the hive, where it releases the chemical over time. But that is temperature-dependent: if it’s too hot, too much of the fumigant will be released and can damage or destroy the hive. Oxalic acid is safer but is only effective in winter, when the colonies are broodless.

The broader problem is that the life cycle of the mite limits the effectiveness of all traditional pesticides. The female varroa mite enters the larval cell and lays its eggs before the cell is capped; the cell remains capped for about two weeks. All the mites and their eggs inside capped cells are protected from any pesticides that are put into the hive. Fumigants rely on two weeks of steady temperatures while synthetic chemical pesticides often harm honeybees or their  ecosystem.

National Geographic photographer, Anand Varma, explains the threat of Varroa mites to bee colonies.

GreenLight’s advantages

GreenLight’s varroa treatment works differently. “We are targeting a protein that’s necessary for the normal functions of varroa,” says Masucci. “Without it, their physiology is disrupted, and so this treatment is highly detrimental to the mites.” A small amount of RNA, applied with gloves rather than a hazmat suit used when applying chemical approaches to pest control, is all that’s needed to induce the effect. Mites have a receptor in their gut that allows them to import the double-stranded RNA into the cell, where it activates its normal cellular mechanisms.

“We are zeroing in on a different stage of their life cycle than current products,” he says, “and what’s novel about this approach is that we are targeting reproductive mites; we deliver it in sugar syrup, which the bees use as they would nectar.” Bees place this syrup containing the dsRNA into cells right before pupation, where the mites get exposed.

Honey bees sit on top of a Greenlight packet full of syrup at the hive of Beekeeper Barry Hart in Barwick, Georgia.
Honeybees feeding on top of a GreenLight pouch full of syrup at the hive of beekeeper, Barry Hart, in Barwick, Georgia.

The RNA in the syrup, which quickly degrades, measurably improves hive health. Masucci says that early studies show an extra frame’s worth of bees per hive, or about a 20 percent bump in production plus a 10 percent increase in hive survival rate compared to conventional treatments. “It’s a small bump,” he says, “but it’s meaningful.” 

Hart, the Georgian bee farmer, has participated in a GreenLight trial of the new RNA solution. Compared to oxalic acid and amitraz strips, he says, the RNA-treated hives seem much healthier. “It helped bring down mites,” he says, and after 35 years of keeping bees, his conclusion: Bees were more active, their hair was glossier and fluffier, and “even the sound a hive of bees makes when you open the top—the hum” was promising.

Changes in the beekeeping industry in recent years led Hart to transition from 100 percent honey production to renting out many of his almost 4,000 hives as pollinators, trucking them around the country for blueberries, squash, cucumbers, watermelon, almonds, strawberries, pumpkins, apples. This spring, 6 semis—each loaded with 480 hives—headed to California. He also sells hives to commercial and hobbyist beekeepers.

Hart believes that GreenLight’s product promises a clear benefit. This year, mainly due to the varroa mite, he lost more than 300 hives. The cost of replacement hives ranges from $225 to $250, and although Hart splits his hives to lessen the blow, it does end up diminishing production. “We get paid on hive strength,” he says, “so another two frames [per hive] could mean another $15, $20 in my pocket.”  

A vital part of plant health as well as a business, honeybees are an indicator of ecosystem health. “You can sit a hive of bees in one location, collect the pollen, and it will tell you the health of the environment within a mile of that hive,” says Hart. “You can see what’s growing from the pollen. If a bee can survive there, the environment is pretty good.”  

GreenLight’s RNA-based solution, which targets just the mite, could go a long way toward helping beekeepers manage the varroa mite while promoting sustainable farming. “You take care of the bees,” says Hart, “and they’ll take care of you.”