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Cannibalizing honey bees target deadly mite that kills colonies

Colony collapse disorder has wiped out hundreds of thousands of honey bee colonies in the US and worldwide Bee breeders at the USDA Honey Bee Laboratory at Baton Rouge La have developed a line of bees with resistance to the varroa mite which vectors viruses that lead to colony collapse
<p><em><strong>Colony collapse disorder has wiped out hundreds of thousands of honey bee colonies in the U.S. and worldwide. Bee breeders at the USDA Honey Bee Laboratory at Baton Rouge, La., have developed a line of bees with resistance to the varroa mite, which vectors viruses that lead to colony collapse.</strong></em></p>
Honey bees with the VSH gene are able to detect bee pupae within the brood nest that have mite families. They cannibalize those pupae and eat the mite offspring as well. If every time the female mite tries to reproduce the VSH bees interrupt the cycle, the mite population declines.

(Second in a series)

First, you have to wrap your head around the fact that there are some among us who are at one with honey bees.

Jeff Harris, Mississippi State University Extension/research apiculturist, has studied honey bees since boyhood.

They know bees from creation to death, their royalty/worker/collective-based hierarchy. They know bee sex (how randy drones congregate in a bee singles bar waiting for a virgin queen to come flying along for some explosive — literally — group lovemaking, after which the drones fall to the ground and die), and if you can imagine such a thing, how to collect bee semen for genetic research (one honey bee drone produces about one-millionth of a liter of semen, and again, he dies).

With the aid of powerful microscopes, they know these winged wonders all the way down to the cellular level.

They scoff at the scare tactics of environmental activists whose websites promote the myth that we’d have a foodless world if all honey bees died out. Maybe there’d be fewer almonds, fruits, and melons, the major beneficiaries of bee pollination. But food production wouldn’t grind to a halt.

And no, cell phone towers don’t jam bees’ navigation abilities, keeping them from finding their way back to the hive.

Jeff Harris is one of those founts of bee knowledge. From hives in the backyard as a boy to his present role as Extension/Research Apiculturist at Mississippi State University, honey bees have been an ongoing part of his life.

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“I had never thought of bee biology as a career field,” he says. “I had just considered it a hobby. Initially, I set out to be a chemist, and started a Ph.D. program in chemistry. I liked the mechanisms, the mathematical and abstract aspects. I was in synthetic organic chemistry, and our job was to find the cheapest route to make a drug that was important to medicine — long hours in the lab, making things, purifying them, verifying them. And I hated it!

“It occurred to me one day, ‘You big dummy, the thing you put most of your energy into, when you’re not at school, is bees. I wanted to be a scientist, but I didn’t know if I could do it with bees.  I started looking around and found that LSU had an entomology department that was associated with the USDA Honey Bee Laboratory at Baton Rouge. I contacted them to see if I could get a master’s degree in entomology, working with honey bees, and I was very fortunate to get accepted and to work with John Harbo, one of the nation’s preeminent honey bee scientists.”

Developing a bee with mite resistance

After Harris earned his Ph.D. in insect physiology, he took a post-doctoral position at the bee lab and after two years became a permanent scientist there. He spent 15 years as a bee breeder, working with other scientists to develop lines of honey bees that express high levels of Varroa Sensitive Hygienic (VSH) behavior — resistance to the varroa mite, a tiny insect that is the vector for viruses that are a major cause of Colony Collapse Disorder, which has killed millions of honey bee colonies worldwide. 

Almonds are the leading U.S. crop relying on honey bees for yearly pollination.

There are only a very few insecticides for control of the mites, and over time the pest has become increasingly resistant to those chemicals.

“It was a relatively simple idea,” Harris says of the VSH work that was begun in 1996, “ but it’s often the simple things that eventually pay off. The Europeans had been dealing with the varroa for 25 years before we got it in the U.S., and they had been trying to breed for resistance, without success. A varroa-resistant line of honey bees was the holy grail in our industry.”

The Harbo team developed a technique using mite-infested worker bees pooled from many different colonies.  They subdivided the mixture of bees and mites to form uniform colonies, with the only difference between colonies being queens with known but varied genetic backgrounds. The scientists monitored mite populations over 10-week to 16-week periods.

“We then chose the queens that grew the lowest mite populations as those with potential genetics for affecting the mites,” Harris says. “Using instrumental insemination (that bee semen, remember) to control mating, we then took the top 10 percent of those as parents for the next generation of queens and drones.

“We started seeing progress the second year. In the third year, when we thought we had resistance, we began producing queens from our best queens and drones and started doing single drone insemination crosses to try and tease out those with the best resistance.

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“With single drone insemination we can mate a queen with just one drone, which is not what happens in nature. This insures that every worker in the colony has the same parents. What’s beautiful about this is that you can find and amplify rare genes. The next season, we’d put those queens out and repeat the test. We did that year after year. Within five years, we knew we had a significant genetic component for varroa resistance.”

A line of cannibalizing bees

The VSH honey bee can detect pupae infested with varroa mites; they then cannibalize the infected pupae and eat the mites in the process.

Bees with the VSH gene are able to detect bee pupae within the brood nest that have mite families, and they cannibalize those bees. “The bee nest can tolerate losing individual bees,” Harris says, “because they’re producing thousands per day from the queen, but the mite family can’t tolerate the interruption. The bees eat the mite offspring as they cannibalize an infested pupa. The female mite will attempt to reproduce only three to five times in her life. If every time she tries to reproduce the VSH bees interrupt the cycle, the mite population declines.”

The bee lab team produced stocks of the VSH bees that are still maintained at Baton Rouge. A cooperator Tom Glenn, in California, who Harris says was “probably the biggest seller of instrumentally inseminated queens in the world,” entered into an agreement with the USDA to disseminate the VSH stock. He then produced breeder queens and sold them across the U.S., helping to distribute the resistance gene. “There’s now an entire body of work to support that this works in the field,” Harris says.

“This is definitely a first step, and where I think where we need to be going for controlling the varroa mite. But all the activist and media focus on pesticides and bees has sort of taken attention away from these unique bees.”

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Because honey bees are quicker to inbreed than most animals, the challenge, he says, is how to sustain a breeding program that focuses on certain traits without inbreeding too rapidly.
“One of the things I’m trying to do here at Mississippi State is establish a breeding plan that is more long term and designed to avoid inbreeding. I’m trying to develop a VSH bee that will be good for Mississippi beekeepers and isn’t inbred.

Weaning beekeepers off chemicals

“The challenge with commercial beekeepers is that we want to wean them off chemicals. Nobody wants to hang miticides in their bee colonies, but you do that or you lose your bees. Commercial beekeepers need something that’s bulletproof — the resistance needs to be so reliable that they incur less than 10 percent loss, and right now we can’t give them that. To get reliability as high as they want it, along with good honey production, bees that don’t sting a lot, and resistance to varroa mites so they don’t have to treat, is is going to take a lot of breeding effort.

Although soybeans don't require pollination by honey bees, they are a major source of honey production for Mississippi beekeepers.—Clemson University photo

“Resistance is there in the VSH bees, and it’s pretty good at times. But a commercial beekeeper with 10,000 colonies needs reliability. If he feels resistance isn’t high enough, he’s going to treat instead.”

The result, Harris says, is that “the commercial guys aren’t trying the VSH stock — they still feel they can rely on chemicals. Until they can get that wonderful bee with all the characteristics they want, they won’t buy into the VSH concept. On the other hand, the hobbyists, the smaller beekeepers, have a different philosophy; they have less to lose, and it’s easier to encourage them to try the resistant bees.

“I’m trying to develop a stock here at MSU in which we select for good honey production, low defense behavior, and varroa resistance. But it’s going to take time. John Harbo and I are still breeding this material, and breeders in Europe are interested in what we’re doing; they’ve used some of our VSH semen.

 “The Europeans have a wonderful bee, the Buckfast honey bee, that has been developed over many generations; it’s extremely gentle, a good honey producer, survives their winters well, and is extremely uniform, and they have a big, coordinated program to avoid inbreeding.

“They loved our resistance, but they didn’t want our semen diluting their outstanding stock. Instead, they wanted to know how we achieved resistance. We’ve met with them many times over the past few years, teaching them how we do things, and they’ve had some remarkable success. They took a bee stock that was already highly selected for all the desirable qualities and then bred for resistance. They’ve amplified the resistance trait, and now they’re looking for someone in the U.S. to distribute their Arista honey bee with resistance to the varroa mite.

“I’ve seen these bees in Europe, and they’re incredibly uniform. We never get that kind of uniformity here — there’s just so much variation in our bees. The European bees are very predictable, and that’s what we need to be shooting for. The Europeans are very excited about this, and I’m looking into the potential for working with them.”

(In our next article, the controversy about honey bees and pesticides, particularly neonicotinoids.)

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