Neonicotinoids: euphoria then death for bees
Two papers published in the journal Nature earlier this week are causing quite a stir in the bee world. The first, “Seed coating with a neonicotinoid insecticide negatively affects wild bees” by Rundlof et al. is unique in that the authors were able to perform controlled field experiments. This is often difficult to do because neonicotinoids are so prevalent in the environment that finding “clean” fields is tough.
But these scientists, working in Sweden, were able to obtain sixteen test plots of oilseed rape (canola). In eight of the plots, the canola seeds were treated with a combination of Clothianidin and a non-systemic pyrethroid. The other eight fields were planted without the insecticide treatment.
Not surprisingly, the wild bees in the treated fields were severely affected by the insecticides. What amazed the researchers was the amount of disruption. They found reduced wild bee density, reduced solitary bee nesting, reduced bumble bee colony growth, and reduced bumble bee reproduction. According to lead author Maj Rundlof, less than half as many wild bees were found in the treated fields, and colonies of bumble bees failed to increase in weight. Oddly, the honey bee colonies in the test appeared normal.
In the second study, “Bees prefer foods containing neonicotinoid pesticides” by Sébastien C. Kessler et al, researchers found that bumble bees and honey bees were unable to taste neonicotinoids but consistently chose syrup containing neonicotinoids over syrup that didn’t. Why? Some scientists believe that the effect of eating neonicotinoids may produce a euphoria in the bee similar to the effect of nicotine in humans.
So, given a choice of flowers—some with the insecticide and some without—bees may prefer the treated flowers because they get a high, even though that choice increases their overall exposure to the toxic chemicals and may cause impairment and death. Sound familiar?
In my opinion, these papers confirm what we bee-lovers have always suspected, which is that wild bees will be far more affected by field-applied pesticides than managed honey bees. Managed honey bees, after all, can be moved out of a field at the close of pollination season, whereas the wild bees cannot leave.
When compared to honey bees, most wild species:
- Are active (and reproduce) during a short season, not much longer than the flowering time of a crop like oilseed rape
- Fly only short distances and so are limited in their food choices
- Live in the soil where the contaminants remain active for long periods
- Have small populations sizes so the loss of a few individuals is significant
How important are these wild bees? How much pollination do they actually do? The answer, I think, is that we don’t really know. But having studied wild bees in graduate school, having spent years watching them, photographing them, and learning to identify them, I believe we underestimate their importance. I also think honey bees get a lot of credit for the work done by wild bees.
Determining their value is difficult because of their size. When we think of wild bees, we tend to think of the monsters: orchard mason bees, bumble bees, carpenter bees, even some of the diggers and miners. But many of the wild bees are so small that most people would never notice them. Some the size of fruit flies look like tiny splinters on a flower or a speck of dirt. Because they are so small and fast, it is hard to see what they are doing. It’s even hard to do controlled studies because they are difficult to screen out of a field or test plot.
But work? These little ones work themselves silly giving us flowers and trees, herbs, seeds, crops, medicinal plants and more.
If we studied only those living things that are easy to see—eliminating molds, viruses, bacteria, and single-celled plants and animal—we wouldn’t have a very good idea of how the world works. Similarly, if we study only the bees that are easy to see, we get a skewed view of how pollination works.
For example, I think a little sweat bee, Halictus rubicundus, may be one of North America’s premier pollinators. Found in all 50 states and most provinces, it seems to be everywhere, but no one has even bothered to give it a common name. When you walk through a field, they scatter like tiny flies, but work side-by-side with the recognized pollinators like honey bees and bumble bees.
Only after we eliminate them—along with the many other silent pollinators—will we know how valuable they were. When that happens, we will be sorry. We will wonder what was ever going on inside our maximum-crop-yield, perfect-produce, chemical-industry-protecting little brains. Of this, I am sure.