Colony Collapse Disorder Is Spreading To Wild Bees

Pesticides, overcrowding, and globalization have transformed bee colonies into pathogen training grounds.

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Jan 20 2015, 10:31pm

​Queen bee in a commercial hive. Image: Waugsberg.

Wild bees are at risk of catching diseases from their struggling domesticated brethren, according to a recent study published in The Journal of Applied Ecology. The study, led by evolutionary geneticist Lena Wilfert of the University of Exeter, adds a new layer to the crisis known as colony collapse disorder (CCD), which has precipitated an alarming drop in honeybee populations worldwide.

CCD is a serious problem—not just for bees, but for the species that depend on them, humans premiere among them. Commercial bees play a crucial role in pollinating the crops that sustain our ever-increasing population, and wild bees actually optimize the performance of these human-managed colonies (in addition to being ecological dynamoes in their own right). Indeed, when it comes to producing substantive crop yields, bees and other insect pollinators are a more effective tool than fertilizer, generating a global food value of about $176 billion each year.

In short: If bees go down, we're going down with them. Literal buzzkill.

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Wild bee pollinating a flower. Image: James K. Lindsey.

That's why it's so disturbing to learn that the pandemics plaguing commercial colonies of bees are spilling over to the wild—and they're not just affecting wild bees. Wasps, ants, hoverflies, and other pollinators are also at risk of hosting and spreading diseases that originated in honeybee colonies.

While some degree of interspecies infection is inevitable, the problem is significantly exacerbated by human activity. For example, treating crops with pesticides, particularly the notoriously toxic neonicotinoid class of chemicals, can lead to weakened immune systems in pollinators, which gives viruses, mites, and parasitic bacteria a much stronger foothold in the ecosystem.

"Beyond the relatively well-understood threat of pesticides, the full breadth of chemicals to which pollinators may be exposed needs to be considered," the authors wrote in the study. "For example, it has become clear that an intact gut microbiome is essential for pathogen resistance, which could be disrupted by chemicals with an antibiotic function."

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Microscopic image of a Varroa destructor mite, a particularly virulent bee parasite. Image: Pollinator.

As we've repeatedly reported, the widespread use of neonicotinoid pesticides is an ecological nightmare that starves songbirds and creates toxic slugs. So, it's not particularly surprising that it also lowers the immunity of pollinators around the world. "Minimizing the exposure to chemicals such as pesticides or acaricides through integrated pest management, which aims to balance the need for pest control with minimal pesticide use, is crucial," wrote the study's authors.

But the use of pesticides isn't the only anthropogenic driver behind the transmission of pathogens into the wild. Wilfert's team also found that many commercial beekeepers are creating ideal conditions for virulent diseases to emerge. "High densities within breeding facilities and in commercial pollination operations increase the contact rate between infected and uninfected conspecifics, thereby lowering the threshold for disease emergence," the authors explain.

This is a particularly dicey issue in genetically diverse populations, because it gives pathogens the opportunity to adapt to a number of different hosts. In this way, colonies can essentially provide a training ground for ambitious diseases, an effect that has already been observed in commercial fish farms.

Along those lines, Wilfert's team emphasized that RNA viruses are the biggest potential threat to wild pollinators, because they adapt very quickly to new hosts. "Fast-evolving RNA viruses, known to cause severe colony losses in managed honeybee populations, deserve particular attention for their propensity to jump between host species and thus threaten ecologically and economically important wild pollinator communities," the authors wrote. To make matters worse, the globalization of the honeybee industry has extended the geographical reach of these diseases in unprecedented ways.

In the end, the upshot of Wilfert's study is that in spite of the havoc this spillover of diseases could wreak, very little is currently known about the magnitude of the problem. But the takeaway is still clear: commercial beekeeping needs a 21st Century facelift. It's bad enough that domestic colonies are collapsing around the world. The last thing we need is for wild pollinators to follow them.