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More bad news for bees, now plant viruses are after them

Colony Collapse Disorder is bad news, even if you hate honey as much as I do. Disappear honey bees doesn’t just mean less honey, they pollinate many plants. The value of honey bee pollination is billions of pounds, dollars or euro.

Bee Swarm
Bee Swarm. Photo Arvydas Simbelis / Flickr

While there’s lots of agreement that the bees are in trouble no one agrees on what the problem is. In fact there’s probably a number of causes, so focusing on one issue as The Problem to be Solved might hide other things that are hurting the bees too. For example recent research has found fungicides could be a problem. This isn’t what you’d expect because fungicides are targeted against fungi, not insects. But a new open access paper in mBio reveals an even more unexpected resource.

Bees may be suffering from plant viruses.

Plants aren’t necessarily the kind of thing you think of getting viruses. It’s not like they sneeze to pass infections on to other plants, but they are stationary, so they can’t escape from disease. A virus that can hitch a lift on an insect would have transport from one plant to another. Unfortunately for honey bees, new research shows that Tobacco Ringspot Virus (TRSV) doesn’t travel with bees, it can replicate inside them.

I found this staggering. Yes, insects and plants do eventually share a common ancestor, but then so do humans. I’d be amazed if I woke up with Tobacco Ringspot Virus one morning, so it’s a puzzle why bees would get it. It’s probably partly because TRSV is an RNA virus.

Genetic code is stored in DNA in animals, plants and so on. The molecule has two strands entwined around each other. RNA is single-stranded molecule. It’s used as a messenger in cells in making proteins, but it’s not stable enough to create viable complex organisms. Viruses can use RNA. The molecule is still unstable, and make RNA viruses prone to mutation. Sometimes that will be bad news for the virus, but sometimes it will mean the virus can hit upon a new way to tackle an environment.

The paper, Systemic Spread and Propagation of a Plant-Pathogenic Virus in European Honeybees, Apis mellifera by Li et al. lists many viruses that can hit bees. They sound unpleasant with names like deformed wing virus (DWV), sacbrood virus (SBV), and black queen cell virus (BQCV). Li et al refer to earlier work that shows healthy bees eating infected food could get the virus from that, so it’s possible that insects could be swapping their viruses when they go out foraging. It means it’s not unusual to find bee viruses waiting in plants for a new host, and plant viruses can travel with insects to get from one host to another.

Li et al. weren’t surprised to see TRSV in bees themselves as they’d make good carriers. What is the surprise is that they could see TRSV replicating in the bees, which meant it no longer needed the plant to reproduce. After hitching enough rides in bees, the virus had finally hit upon a way to exploit them directly and they could reproduce throughout the body. Even then this might only be bad news for individual bees. How could the virus get from one bee to another without a plant? This is where the bees are out of luck.

Along with all their other troubles bees have a parasite, Varroa.

Varroa’s species name is Varroa destructor, and it is very bad news for bees. It’s a mite that attaches to bees and lives off their blood. They can collapse a colony in a few years. Li et al. examined Varroa for TRSV and found it in the gut (technically gastric cecum). They didn’t find it elsewhere in Varroa, which means that the parasites might be passing round an infection that does them little harm. It’s yet another pain for the bees. Varroa cannot be eradicated from colonies, so this is an ongoing concern.

To support their argument the authors point at other work, such as the discovery of Flock House Virus, an insect virus, replicating in plants – effectively going in the opposite direction to TRSV. Despite its name Tobacco Ringspot Virus infects a lot more than just tobacco. It means that a long term solution to Colony Collapse Disorder is likely to have to look father afield than just the immediate colony.

Thanks go to Sarah Irons for pointing me at this.

Image

Bee Swarm. Photo by Arvydas Simbelis / Flickr [cc]by[/cc]

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