Honeybees, the Environment, and Pesticides
Honeybees are important for more than just making honey. They also pollinate a lot of our crops — one-third of them, in fact. But a common narrative emerging these days is that the bees are dying. Beekeepers have reported losing substantial fractions of their colonies each winter over the past decade or so. In other cases, piles of dead honeybees have turned up.
Environmental and other public-interest groups often cite pesticides as a leading culprit. In particular, they want regulators to ban a specific group of pesticides known as “neonicotinoids.” Activists argue that these pesticides not only kill honeybees, but may be behind the different, more mysterious set of symptoms known as colony collapse disorder (CCD). This week, 125 public-interest groups asked the Environmental Protection Agency to consider pulling these pesticides from the market.
How responsible are pesticides for the plight of honeybees? We don’t have much clear-cut evidence. But that lack of evidence shouldn’t offer us comfort. Here’s why.
Neonicotinoids’ bee impacts, in a nutshell
Neonicotinoids are a relatively new form of pesticide designed to target aphids, termites and other pests. What makes them unique is that they’re systemic — the plant itself actually absorbs the pesticide into its leaves and tissues. That helps farmers because they don’t need to repeatedly spray their crops with the chemicals.
But the pesticide also ends up in pollen and nectar, which honeybees consume. Laboratory studies have shown that the neonicotinoids can kill bees. And in recent years, some research has shown that some neonicotinoids have subtler, “sublethal” impacts on bees, harming their flying or food-foraging abilities.
And still more research has found that neonicotinoids could induce at least some of the symptoms of CCD, although these findings have proved to be controversial. In CCD, adult worker bees abandon a colony, but the queen bee and immature bees remain; few dead bees, if any, are found outside the hive.
Case closed? There are a few reasons why it’s more complicated than it seems. First, pesticides’ effects on individual bees don’t necessarily equate to the effects on a colony. Thousands of bees live together, collectively functioning as a super-organism. And this super-organism can still keep functioning even if some of its members get sick or die.
Additionally, bees in nature are exposed to dozens of other pesticides and other hazards such as habitat destruction and parasites, all of which may work together to hurt them. It’s also worth noting that bee deaths aren’t a one-size-fits-all proposition; not all of beekeepers’ recent colony losses are caused by CCD. Piles of dead bees are sometimes confused with CCD as well.
What we don’t know
Given those factors, would banning neonicotinoids cut losses of bee colonies? Not all scientists are convinced. And we still don’t have much evidence that neonicotinoids themselves are linked specifically to CCD. Here’s why that’s no reason to rest easy: We may lack evidence right now. But that dearth of evidence could stem from gaps in the scientific methods that regulators rely on.
To go on the market here or in Europe, pesticides must pass tests called “risk assessments” to show that they wouldn’t be unacceptably toxic to humans or wildlife. Among the creatures for which regulators study pesticides’ risks are honeybees. The problem: Traditional lab tests on bees told us only how much pesticide it takes to kill them, while ignoring impacts on behavior, flight or foraging abilities. The tests also didn’t necessarily tell us what would happen at the colony level, in the long term, or with multiple pesticides at a time.
The Environmental Protection Agency and the European Food Safety Authority have been working to address these problems. They’re trying to improve bee risk assessments by adding a round of field studies; these would be performed in the event that laboratory tests raise any red flags. These field studies, although cumbersome and expensive, could tell regulators how real-world doses of pesticides affect whole colonies. Regulators also want to use new laboratory tests to identify other red flags — such as longer-term/”chronic” effects and sublethal effects — that would trigger these field tests. But many of these tests aren’t ready for use just yet.
To bee, or not to bee banned?
What do we do about the neonicotinoids, then? It boils down to how cautious we want to be. The European Union decided it wasn’t going to take any chances, so it banned neonicotinoids for two years, saying not only that the pesticides can kill bees but that they may carry other risks we aren’t aware of yet.
But in the United States, the burden is on regulators to show that a pesticide is unacceptably risky before they can ban it. And in many cases, regulators here can give pesticides an early stamp of approval if some risk data is missing. This practice of “conditions registrations” has proved controversial, including for the neonicotinoid pesticide “clothianidin.”
In short, there are a lot of potential ingredients that could be driving honeybee deaths. But we still don’t know exactly what this lethal recipe is, especially in the case of CCD and winter colony losses. If pesticides — and neonicotinoids, specifically — are involved, however, they may not be acting alone. And it’s unclear whether barring them would save the bees. But the scientific gaps we see here illustrate an important fact: Absence of evidence doesn’t always mean evidence of absence.
