Parasite Fly Turns Bay Area Honeybees Into 'Zombies'

Researchers at San Francisco State University have found a potential new threat facing honeybees in the Bay Area. It’s a fly parasite that preys on native bees and paper wasps, but for the first time, they’ve found it in the European honeybees that are the backbone of California’s agricultural industry. The parasite could also be causing some very strange zombie-like behavior in the bees. I spoke to John Hafernik, Professor of Biology at San Francisco State University, about what he found.

How did you first find this parasite?

It was really serendipity. I was walking into the biology building one morning and noticed a large number of stranded bees in front of the building. I picked them up to feed to a praying mantis that I had down in the entomology lab. One day I forgot the vial of bees on my desk. I came back a few days later and it was full of fly pupae that look like small brown pellets. I knew something strange was going on with the bees.

So what does this parasitic fly do to the bees?

We think the foraging honeybees are out collecting nectar when they encounter these flies. The fly jumps on the back of the bee and uses a long egg-laying device to insert its eggs in between the segments of the bee’s abdomen. Then the bee flies off back to the hive. Soon, the maggots hatch inside the bee and start eating the internal contents of the bee.

At some point, that alters the bee’s behavior and the bee leaves the hive. We find they abandon their hive at night, which is a really unusual time for bees to be active. Basically it’s a death flight for the bee. We’ve termed it the “flight of the living dead.” They set off to die somewhere alone and if there’s a light nearby, they’re attracted to the light. They’re often disoriented, walking around in circles, almost as if they’re a drunken bee.

Once they get stranded, then it takes another five to seven days for the maggots inside to complete their life cycle. They eat all the wing muscles in the bee and then push their way out between the head and the thorax. We’ve found up to 15 maggots coming out of a single bee.

That’s pretty gross…

Not a pleasant way to go for the bees. If I were going to pick among the parasites and pathogens that bees get, this would be right at the bottom of the list. They’re literally writhing inside you and eating your innards.

So it’s possible that the fly parasite is controlling the bee’s behavior?

That could be the case here. It gets the bee to flee the hive and land in a place that’s better for the parasite. If the maggots hatch inside the hive, they could be attacked by worker bees. So it might be better for them to get outside.

At this point we don’t know that for sure, though. The bees could also be committing altruistic suicide to take this parasite away from their hive mates. Bees are very careful about keeping a clean hive. There are even undertakers bees that will grasp bees that are sick and fly them out.

How can an organism make another organism into a zombie?

It could be that they’re producing a neurotransmitter mimic that affects the bee’s behavior. Or it changes the expression of genes in the bee that control their daily behavior patterns or their attraction to light.

There is some work that’s been done on a caterpillar virus that turns on and off the genes for caterpillar behavior. It induces the caterpillar to crawl up high and then die and rain viruses down to other caterpillars.

That’s incredible.

This is one of the reasons we do science – to find the unexpected. You don’t think you’re going to find something new just by walking into your office in the morning. The intricacies of the natural world are amazing.

What effect is the parasite having on honeybees?

We’ve sampled a hive here on campus and we find parasitism rates are 5% to 20%. It’s a lower percentage than some of the viruses and infections they might have. But this is always a death sentence for the bees that have it, unlike some viruses. And as bees abandon the hive, they potentially disrupted the colony organization. A 20% loss ends up being a lot of bees over time. This parasite peaks over the fall and winter, when the bees are already under the most stress.

And you think it could be connected to Colony Collapse disorder?

We’re not saying we have the smoking gun. We have something that’s associated with one of the symptoms of Colony Collapse that is hive abandonment. It could be a major player or a bit player. The fly parasite is found all over North America.

Beekeepers are still seeing Colony Collapse and there’s still not clear explanation on what causes it. The best guess is that it’s a combination of things. We’re hopeful that now that we have a specific organism that associated with hive abandonment, maybe we can use that as a window into understanding why bees would leave their hive.

Why is it such a danger?

Honeybees are an integral part of our agricultural system, especially here in California. They’re moved from field to field to pollinate our crops like almonds and fruit trees. A large percentage of the things we eat are there because bees were there to pollinate them. They’re amazing creatures that have incredible social organization.

What’s next for your research?

We really want to know how widespread this is. And we also want to know what’s going on within the hive and how the bee’s behavior is being altered by the fly. We’re interested in looking at the genes inside the bees to see if the parasitized bees are expressing genes differently.

I’m really impressed that you didn’t use the pun “zom-bee” during this interview.

I’ve used it in many other cases. It’s too perfect.

To learn more about other zombies in the insect and animal world check out Discover Magazine’s slideshow of eight other infestations, or the below Planet Earth segment on a parasitic fungus.