Closing in on the bee killers

By now you’ve no doubt heard that honey bees (Apis mellifera) are dying off in great numbers all over the world. This isn’t just tragic for bees and apiculturists. Bees are responsible for pollinating $15 billion worth of crops in the U.S. alone. We’re not just talking about honey. Without bees, we wouldn’t have more than 90 of our favorite fruits and vegetables. About a quarter of the human diet is utterly dependent on honeybees. 

As you can see from this video, there have been many culprits named in the demise of the honey bee. Pesticides, fungicides, parasites, toxins and habitat destruction have all been blamed. Thanks to new research from the University of Maryland, the Bee Research Laboratory and USDA-APHIS, we may finally be able to say what's causing the die off. Unfortunately, it's all of the above.

How might these different factors interact? Although not in themselves lethal to bees, insecticides and fungicides can alter bees’ enzyme activity, which in turn can effect development, behavior and immune function. Combinations of these chemicals might affect bees' life cycles and make them more susceptible to diseases like those caused by the parasite Nosema.

Until recently, these interactions were missed simply because scientists had been testing single chemicals on bees. Instead of repeating that practice, researchers led by Dennis vanEngelsdorp of the University of Maryland collected pollen directly from foraging bees. They then identified and quantified the number and type of insecticides, herbicides, fungicides and other chemicals associated with those pollen grains. In that way, they figured out what combinations of chemicals bees actually encounter while going about their business. 

All the pollen samples contained various insecticides and fungicides, and a quarter contained herbicides as well. This might be a good place to point out that bees feed pollen to their young.

Pollen from these same fields were fed to bees that had been inoculated with Nosema. When introduced in the combinations found in actual fields, the various pesticides did not have the same effect as when they’d been tested individually. In particular, pesticides commonly used by beekeepers themselves to control hive mites made the bees twice as susceptible to Nosema infection.

This is all, of course, very bad news for people who were hoping for a quick fix to this problem. As vanEngelsdorp explains:

The pesticide issue in itself is much more complex than we have led to be believe. It’s a lot more complicated than just one product, which means of course the solution does not lie in just banning one class of product.

This year, the European Union has decided to ban the use of insecticides known as neonicotinoids in an effort to save their bees. However, in this study, neonicotinoids were only present in apple pollen and were associated with decreased risk of Nosema infection. Clearly, banning a single chemical is not going to save our bees.

To make matters worse, regardless of hive placement, bees often returned with wild pollen. Because so much of the collected pollen did not come from the intended crop but from nearby wild flowers and weeds, the authors suggest that beekeepers investigate spray programs in nearby fields as well as the ones in which they’re placing their hives. This will make controlling for chemical contamination all the harder.

Hat tip: Cathy Earle.

Jeffery S. Pettis, Elinor M. Lichtenberg, Michael Andree, Jennie Stitzinger, Robyn Rose, & Dennis vanEngelsdorp (2013). Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae PloS ONE DOI: 10.1371/journal.pone.0070182.