There's widespread agreement that bees around the world are in trouble. A few years back, domestic honeybee nests started experiencing mass die-offs, and problems were found in wild bees as well. What hasn't been clear is what the cause might be. Viruses, fungi, and pesticides have all been floated as possible causes, but definitive evidence has been hard to come by; a number of scientists have suggested that there might be multiple contributing factors.

Nevertheless, suspicions focused on a specific class of insecticides called neonicotinoids. The EU has already placed restrictions on their use, and it's considering a near-total ban.

If you read the headlines this week, it would appear that a new study completely justifies that decision. Funded in part by two insecticide manufacturers, a team of independent researchers purportedly tied neonicotinoids to bee colony health. But a quick look at the underlying data shows that the situation is far more complex. And a second paper, with more robust results, supports the idea that these insecticides are merely one of a number of factors contributing to bees' problems.

Not much significance

One of the two papers, by a group of European researchers, was meant to be definitive. They obtained a waiver from the EU to use neonicotinoids in fields in three countries: Germany, Hungary, and the UK. Different fields received either one of two different neonicotinoids or were untreated and acted as controls (untreated fields still received normal applications of other agricultural chemicals). Honeybee colonies were set up nearby, and the researchers found nearby nests of wild bees to track their health. If anything could make matters clear, this study seemed designed to do so.

It didn't.

The researchers used various measures of bee and colony health for both domesticated and wild bees, a total of 14 tests in all. But that was 28 tests when you consider they did two different insecticides, and 88 once you consider that they analyzed each country separately. Using the standard measure of statistical significance—only a five-percent probability that a result was produced by chance—means that this many tests almost certainly produced a few significant results by chance.

Making matters worse, the UK fields had horrible over-winter survival, including in the controls, so the numbers weren't high enough to perform any statistical analysis at all. (On the plus side, that cuts us down to 70 individual statistical tests.)

In the United Kingdom, high hive mortality precluded a formal statistical analysis of overwintering worker numbers. The majority of the remaining results weren't statistically significant. That leaves us with just eight results that stood out above background noise. And, among those eight results, it appeared that the insecticides were protective in three of them. In other words, hives near the treated field had healthier bee colonies.

Two of those protective results came in Germany, where no significant negative effects were seen. Astonishingly, the researchers use that to conclude there are "country-specific effects" in how the insecticides influence bee health. They go on to write that, "These findings point to neonicotinoids causing a reduced capacity of bee species to establish new populations in the year following exposure." It's hard to understand how the confused set of results justifies either of these conclusions.

Not much significance

The more likely issue is that, despite the excellent experimental design, there were too many other factors influencing bee health. Fortunately, a second paper was released at the same time, and it has somewhat clearer results. In this case, the authors went into the field and measured the levels of neonicotinoids in hives near agricultural areas. They then created a series of their own hives, both treated with similar levels and left untreated as controls. All animals were given an RFID tag and put in a common hive to keep conditions as similar as possible.

Here, there was a consistent pattern of results. The neonicotinoid treatment reduced the lifespan of the bees, caused them to leave the hive earlier, and reduced their grooming behavior. Colonies that were treated were also less likely to replace their queen if she left in a swarm.

But constant, chronic exposure was needed to see some of these effects, which grew more severe over time. And in their survey, the researchers found that most colonies in agricultural areas had neonicotinoids present from May until August.

The Canadian team also looked at whether insecticides were the entire problem by exposing the animals to a number of agricultural fungicides, which are often used in parallel. They found that one of the four tested (something called Boscalid) enhanced the lethality of the insecticide. That's consistent with the idea that, while neonicotinoids aren't helpful to bees, they're only part of the problem that's leading to colony collapse.

Science, 2017. DOI: 10.1126/science.aaa1190, 10.1126/science.aam7470 (About DOIs).