Honeybees, worth almost $20 billion to American agriculture, are worth protecting — and a new biological weapon scientists discovered may help combat honeybees’ main enemy, aptly named the varroa destructor.

The varroa destructor is a parasitic mite responsible for decimating honeybee hives. Now, in an effort to save bee colonies, researchers are tapping into an unlikely ally: the bacteria that live in bees’ guts.

In a January 2020 experiment, scientists engineered gut bacteria that occurs naturally in bees. The results, they reported, were astounding — the mites died after ingesting the manipulated bacteria, while the bees’ own immune systems were strengthened.

Outside the lab, researchers say they hope the technique can be scaled up to rescue full colonies.

But there’s a long road ahead.

Since the 1940s, the number of hives in the U.S. has nose-dived from 6 million to 2.5 million. From 2018 to 2019 alone, U.S. beekeepers lost more than 40% of their colonies, according to the Bee Informed Partnership.

A combination of colony-killing foes are blamed, but researchers say varroa mites pose the greatest threat.

“Varroa mites are the worst,” said Laura Lavine, entomology department chair at Washington State University. “They’re the most imminent threat to beehives in North America today.”

The mites kill bees by feeding on their fat stores, said Tim Hiatt, a commercial beekeeper and member of the Washington State Beekeepers Association. They also carry the deadly “deformed wing” virus, which they transmit to bees.

To put this in human scale, molecular biology researcher Sean Leonard said to imagine a mammoth tick clinging to you and feeding off your body.

“It’s like having a giant tick the size of your face sucking your blood,” said Leonard.

Leonard is a graduate student at the University of Texas studying cell and molecular biology. He is part of the research team that discovered the potential solution to combating varroa mites.

Leonard and his colleagues engineered double-stranded RNA to use as ammunition against varroa mites and the virus they carry.

RNA, or ribonucleic acid, exists in all living cells. Its main role is to act as a messenger, carrying DNA’s protein-coding instructions to a cell’s reproduction machinery. But RNA can also be used to shut down invasive genetic materials.

The team of scientists at the University of Texas at Austin used two similar but distinct techniques, one for killing the mites and another for combating the virus.

To attack the virus, the scientists used a preventive technique similar to vaccination in human or animal medicine. Using double-stranded RNA, they introduced a small portion of the genome into the bee, which strengthened the bee’s immune system against the later invasion of a full-scale virus.

“If you could compare it, it’s almost like getting a vaccine,” said Leonard.

To kill the varroa destructors, the research team attacked the mites’ immune systems directly.

Leonard figured out how to genetically modify Snodgrassella alvi, one of the bacteria in a bee’s gut, so it would produce RNA that matched the genetic material he wanted to dismantle.

The team then put the engineered bacteria into sugar water and fed it to honeybees. Later, when the mites fed off the bees, they ate the engineered bacteria — and died. The mites, which were forced to dismember some of their own genes, had been tricked into killing themselves.

Mites were 70% more likely to die on treated bees, and bees infected with the virus were 36% more likely to survive, the team reported.

“When we got those results in, we definitely started to get excited,” said Leonard. “I think this is such a promising technology. But we don’t have a marketable product yet.”

The techniques, though exciting, won’t immediately be available to beekeepers.

Critics are concerned about the use of engineered bacteria outside the lab, since bacteria in the wild are not easy to contain. Leonard said caution is crucial, but because the bacteria are not known to exist outside bees’ guts, he is not worried about cross-species infection.

Experts agree that more experimental work needs to be done on hives in controlled settings before testing the effectiveness on a mass scale.

It will take time, research, industry partners and funding to make this work, said Leonard.

Through his research, Leonard has developed an appreciation for bees.

“I’ve come to love these fascinating creatures,” he said. “There’s something amazing about opening a hive and seeing thousands of bees crawling all over and working together.”

When he completes his Ph.D., Leonard said, he hopes to join the ranks of U.S. beekeepers — hopefully in a world with fewer threats from varroa mites.