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New clues to the mysterious bee die off

Female phorid flies will land on a bee and pierces the bee's abdomen, allowing the fly to lay its eggs inside where they will feed on the bee and eventually kill it. (Photo: Christopher Quock/ San Francisco State University)

One morning on his way into work, AAAS member John Hafernik noticed several bees lying on the ground, weak and not aggressive enough to try to sting him. Thinking nothing of them, other than they would make good insect food, he picked them up and fed them to the new praying mantis in his lab. After doing this for several weeks, Hafernik stopped by his office one day before going to the lab and misplaced a vial filled with several bees on his messy desk. About a week later, when the vial resurfaced, fly pupae and maggots surrounded the now-dead bees.

"At that point I knew the bees had some things happening inside of them, and this was not just the normal stranded bee that had died at the end of its life," said Hafernik.\So that led to a sort of bee detective story, trying to piece things together and understand what was going on."

Honeybees are in trouble; many researchers are trying to figure out why bees keep dying. In 2006, beekeepers suddenly began reporting that their bees were vanishing. Beekeepers would leave seemingly healthy hives, then return in a few weeks or months to find the hives empty with only the honey and baby bees surviving. The worker bees had flown away, abandoning their hives, and presumably all died. Beekeepers have reported losing 30 percent of their hives every year, an odd phenomenon that has given rise to the term Colony Collapse Disorder, or CCD, which is potentially harmful to humans as well. We need bees to pollinate our agriculture and if they were to disappear, food prices could skyrocket. Hafernik's detective work eventually lead him to a parasitic fly which may give us some insight into how to stop CCD.

After seeing the pupae, Hafernik, a professor of biology at San Francisco State University, left them in the vial on his desk where they eventually emerged as small adult flies. He recognized them as a type of phorid fly, a group of flies common across the U.S., Canada and many other regions of the world. He contacted Brian Brown at the National History Museum of LA County, who recognized them as the widespread Apocephalus borealis, a parasitic fly known to attack bumblebees and wasps but not honeybees. This excited both researchers, who, after confirming that it was indeed the same fly, wanted to learn if others had found this honeybee parasite as well.

Hafernik contacted Eric Mussen of the University of California at Davis to see if these flies had ever been reported in honeybees before. Mussen said no, but that he was hearing odd reports of dead bees being found below porch lights. Hafernik was intrigued.

"I walked back outside and instead of looking down, like before, I looked up and there were a row of lights ... And those lights shine down directly on the hive below them," recounts Hafernik. "At that point, we thought the bees were essentially flying a beeline directly from their hives to the light. And that meant the bees were flying at night and basically leaving their hive for a one-way flight."

It is unusual for honeybees to fly at night; they need the sun to navigate, said Hafernik. It was also puzzling why the bees would be attracted to a light. Since bees found near the light had much higher rates of parasitism than bees sampled flying during the day, Hafernik postulated that the parasite must be somehow compelling the bee to abandon its hive at night.

The fact that bees were leaving their hives was particularly important. One of the most puzzling parts of CCD is that the bees disappear; researchers have found many pathogens that harm and kill bees, but have been puzzled about why they would abandon their hives.

Possible reasons for what causes CCD vary widely, from virus infections, malnutrition, climate change and even electromagnetic interference from cell phones. But researchers today don't think any one of these is the cause; instead, different things are combining to hurt the honeybees.

"Its entirely possible that the cause is something that no one has thought of. But I think, at this point, the evidence does not back up any of these theories. But I like to keep an open mind because crazy things can happen with bees sometimes," says AAAS member Reed Johnson, assistant professor of entomology at Ohio State University, who studies drug interactions and diseases in bees.

Beehives today are commonly infected with Varroa destructor mites, a particularly nasty parasite that kills bees almost worldwide, as well as other viruses, bacteria, and fungal infections. Beekeepers also move their hives from state to state across the country, using their bees to pollinate different crops, and thus exposing the bees to countless other health problems. Johnson is researching the interactions between these different threats and the drugs used to protect bees. (Learn more about drug interactions and CCD in this blog post.)

Researchers think it is some combination of these factors that causes CCD, but haven't found a component that compels bees to leave their hives. That is why Hafernik's findings could be a crucial key.

Hafernik realized he needed to better understand the parasite to learn why the bees would abandon their hives and see if it could happen en masse as in CCD. In lab tests designed to discover how the bees got infected, he learned that a female fly lands on a honeybee's back and lays eggs inside the abdomen region. The bee, presumably a forager, doesn't seem to be affected at first; it continues to do its duties, flying in and out of the hive collecting nectar and spreading pollen. Then, sometime later, the infected bee wakes up in the middle of the night and flies out of its hive, never to return.

Watch flies infect a honey bee

Hafernik and his team are now hard at work learning other details about this parasite. He hopes to discover why the phorid fly parasite prompts bees to leave their hive, as this could be the key to understanding this symptom of CCD.

"If they abandon the hive when they are parasitized, is that because the parasite is somehow manipulating the bee?\" Hafernik asked, \"Or is it the bee somehow responding to having a parasite or a pathogen in it and leaving its hive in a sort of altruistic suicide to protect its hive mates? Might [the bee] have a similar behavior for other types of parasites, pathogens and other things [that we could] sort of tease together to see what produces the symptom and better understand colony collapse?"

Hafernik also wants to find out how widespread the infection is. Seventy-seven percent of the hives in the San Francisco Bay area were found to have phorid fly parasites, but Hafernik is working on ways to let citizen scientists test local hives in different parts of the country.

"I've been getting e-mails from all across the country of people reporting similar kinds of observations of bees at light, but whether these bees are actually parasitized by phorid flies, or it's there for other reasons, we don't know at this point," said Hafernik.

This fly has other effects on bee health as well. Tested bees that are infected with the phorid fly were found to have a myriad of other issues, from deformed wing virus to fungal infections, says AAAS member Andrew Core, one of Hafernik's former students and a coauthor on the paper. Core also won the Geraldine K. Lindsay Award for excellence in the natural sciences at the annual meeting of the Pacific Division of the AAAS for his presentation on the bee research.

While the fly may not cause CCD, it could be spreading some other pathogen that hurts bees in other ways. That's one of the issues with Varroa mites; they also carry a number of bee pathogens. Researchers keep finding things that hurt bees, but still don't know what is causing the disorder. Chance and a keen observation are how Hafernik and his team found this parasitic fly, and those same tools may be how we find a way to stop CCD.

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Representative Image Caption
Female phorid flies will land on a bee and pierces the bee's abdomen, allowing the fly to lay its eggs inside where they will feed on the bee and eventually kill it. (Photo: Christopher Quock/ San Francisco State University)
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