Colony collapse clue: exhaust confuses honeybees’ sense of smell


It seems that the ongoing phenomenon of Colony Collapse Disorder (CCD), which has been affecting North America’s honeybee colonies since 2006, is influenced by more factors than anyone had guessed, including automobiles, according to National Geographic.

At the heart of the problem lies the little-known data set that suggests our machines are consuming more than just gasoline. According to a recent study published in Scientific Reports magazine, fuel exhausts eat up odors that help direct honeybees to the plants they pollinate and from which they collect nectar.

Disruption to the bees’ olfactory senses is not a newly recognized phenomenon; in fact, it has been reportedly caused for years by pesticide use, ground-level air pollutants and ultraviolet (UV) radiation.

For honeybees, the sense of smell is not merely a practical convenience, but an essential life skill. Bees rely primarily on the sense of smell to locate their food. Odor cues indicate everything they need to know about every flower they visit. It has long been thought that air pollutants obscured these odors, but it has just recently been determined that the chemical composition of exhausts physically alters the chemical makeup of floral scents in a decomposition reaction.

This recent study, based in Southampton (U.K.), focused specifically on two particular components of oilseed rape flowers’ scent: farnesene and terpinene. It was found that the burning of even low-sulfur fuel in the flowers’s vicinity degraded the makeup of both of these compounds. Honeybees are so sensitive to scent that even the removal of two (of many) odor compounds altered their reaction to the flowers.

As noted by Tracey Newman, the study’s co-author and neurobiologist at the University of Southampton, “even changes in one of the very minor constituents of the mixture caused a major change in the responsiveness of the bee to the smell.”

The blame doesn’t rest on any particular type of fuel or consequential emission, but on internal combustion engines, according to another of the study’s co-authors, Guy Poppy. Compounds that contain both nitrogen and oxygen are at the heart of the issue — and every fuel source used by internal combustion engines. These compounds are present in every fuel from diesel to gasoline and to even the newer alternatives, such as ethanol and biodiesels.

While nitrogen dioxide (NO2) gas emissions are frequently addressed and discussed in relation to the greenhouse gas effect, nitric oxide (NO) typically slips under the radar because it is much less associated with climate change. As a result, both the United States and European Union governments limit levels of nitrogen dioxide in fuels, while the nitric oxide content tends to be ignored.

Yet this lack of attention may not be the primary issue: there are two sides to every coin. According to Jose Fuentes of Penn State University, nitric oxide gases may have only an indirect influence on floral scents. The gases are known to react with sunlight and air, resulting in the production of ozone (or ground-level smog), which could be the real cause of odor composition breakdown. Fuentes also notes that the levels of emission employed by the study were overkill, even compared to the height of rush hour.

Whatever the case may be, honeybees undoubtedly face a number of difficulties, some or all of which have contributed to the outbreak of CCD, and some of which may yet remain unknown.

About the Author

Natasha Strydhorst

Natasha Strydhorst is a Chimes Science and Technology writer, previously section editor, for the 2015-16 school year. She is a senior writing and environmental studies major from Calgary, Alberta (Canada). She enjoys reading, writing, the great outdoors, and virtually any combination thereof.

View all posts by