Fuel Harass Disrupts Smell Signals for Honeybees

A honeybee investigates an oilseed rape flower. AВ fresh probe provides evidence of how fuel harass switches the chemical composition of floral odors, scrambling the odor signals for pollinators.

Photograph by Nigel Cattlin, Alamy

To a bee, no two flowers smell fairly the same. When honeybees forage for flowers, they search for, learn, and memorize distinctive floral scents and comeback to the hive to tell other bees what they’ve found through their famous waggle dance.

It is an significant ritual that is being disrupted by one of the most pervasive forms of air pollution—diesel exhaust—according to a fresh probe published Thursday in Scientific Reports. The research pinpoints the mechanism by which the fuel-combustion pollutants degrade certain chemicals in floral odors. The absence of those chemicals affects honeybees’ capability to recognize the smell. (See related quiz: “What You Don’t Know About Cars and Fuel.”)

Engine harass is hardly the only threat facing the honeybee. It is well recognized that exposure to numerous pesticides can impair bees’ olfactory abilities, while ground-level ozone, or smog, and ultraviolet (UV) radiation can also degrade floral odor compounds that bees pick up on. Authorities around the globe are grappling with how to address the little-understood cyclical diseases that are causing colonies to dwindle. (See related, “The Plight of the Honeybee.”)

The fresh investigate offers insight into the specific hazard for pollinators from the fumes from cars, trucks, trains, ships, and powerful machinery. Significantly, the explore indicates that honeybees haven’t been helped by the “cleaner” diesel now used in Europe and the United States due to regulations that over the past decade eliminated sulfur from the fuel. The researchers used ultra-low-sulfur diesel fuel in their experiment. (See related: “Pictures: Cars That Fired Our Love-Hate Relationship With Fuel.”)

Thousands of chemical compounds contribute to flower odors, so honeybees (Apis mellifera) need a discerning sense of smell. “A honeybee might see a crimson flower, and say oh is this a flower that I want to visit, and [it] uses odor cues to figure out if it’s worth visiting,” said Quinn McFrederick, an ecologist at Fresno State University in California. Odor cues can tell bees which flowers have the most nutritious nectar and pollen for harvesting.

Scientists have long thought that air pollution masked these key floral scents, but the fresh examine provides evidence of how the harass actually switched the chemical composition of the odors. Using an odor palette from a common target for honeybees, oilseed rape flowers (Brassica napus), a research team at the University of Southampton in the United Kingdom exposed the compounds to diesel fumes from a generator fueled by ultra-low-sulfur diesel. Almost instantly, the diesel fumes commenced violating down two of the flower odor compounds: farnesene and terpinene. After training honeybees recognize the flower smell, the researchers liquidated both degraded compounds from the mix.

“To our surprise, indeed, we witnessed that even switches in one of the very minor constituents of the combination caused a major switch in the responsiveness of the bee to the smell,” said Tracey Newman, a neurobiologist at the University of Southampton and a co-author of the explore.

The researchers said one component of diesel harass takes the blame for this degradation: NOx gases, compounds that contain both nitrogen and oxygen, reacting with volatile floral odors. Albeit the scientists used diesel fuel, which powers the majority of cars in Europe and almost all powerful vehicles around the world, NOx gases also are emitted by gasoline, or petrol, and even alternative fuels like biodiesel and ethanol. (See related, “Biofuel at a Crossroads.”) “The bottom line is I don’t think one can embark pointing one’s finger at biodiesel, diesel, or petrol,” said Stud Poppy, an ecologist and co-author on the examine. It’s a larger issue with internal combustion engines, he said.

Both the United States and the European Union use nitrogen dioxide (NO2) levels as a proxy for all NOx gases and have set thresholds for the amount of NO2 in the air, but not for nitric oxide (NO) levels. Poppy said, “These are the sorts of emissions that are sometimes left out from the discussions about climate switch because these emissions are not ones as strongly associated with greenhouse gases.” (See related “Pictures: A Infrequent Look Inwards Carmakers’ Drive for fifty five MPG.”)

Oilseed rape flowers aren’t the sweetest smelling blooms. “They’re actually a bit stinky,” Newman said. But, their odors are very well understood, and these two degraded compounds emerge to be a key element of odor communication for bees. Other bee species and other pollinators rely even more intensely on smell over longer distances. So, the findings could have major implications for other pollinators as well, said McFrederick, who was not affiliated with the explore.

Interestingly, the degraded compounds in this experiment were present only at low levels, and removing terpinene by itself led to a significant decline in bee recognition in the experiment. “That suggests that that in some way kicks off a particular pathway in the odor perception abilities of the animal,” said Newman.

The researchers’ next step is to look at the influence of diesel on the honeybee jumpy system.

How will these findings play out in the real world? “The probe clearly illustrates that airborne pollution can perniciously influence the capability of bees to locate food,” said Jose Fuentes, a meteorologist at Penn State University who was not associated with the examine. Fuentes spelled out two cautions: The experimental levels of pollutants were high even for urban rush hour; and the influence of the NOx gases might actually be an indirect one. That’s because NOx gases notoriously react with air and sunlight to make ground-level ozone, or smog, which may be the actual culprit in disrupting the floral odor compounds.

Urban environments expose honeybees and flowers to more diesel harass, but there are many significant factors affecting the success of hives. The kind of neighborhood gardens found in urban and suburban areas also might provide bees with longer lasting food sources than in rural areas. Field studies could shed more light on the influence of air pollution. “What we need to know is [for] a flower sitting in a field next to a car in a motorway, whether there actually is going to be a plume of smell coming from that flower and whether it’s going to be significantly affected because of the harass fumes,” said Poppy. The worst-case screenplay would be to find a drastic reduction in honeybee foraging and pollination.

While it’s unclear how much influence diesel pollutants might have on pollination, the fresh explore indicates that harass should be added to a growing list of known threats.

“Honeybees living in a modern world face many stresses,” including diseases, insecticides, and atmospheric pollutants, Poppy said. “Probably bees can cope with most of these stresses in isolation or when just two or three of them come together. But, when they all come together at the same time, one might embark to see significant effects and that might explain some of the things we’re eyeing … with pollinators being lost around the world.”

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