Diesel Exhausts Hinder Honeybee’s Ability to Smell and Forage

The honeybee population is battling a new threat- diesel exhaust. Researchers at University of Southampton claim that air pollutants emitted from diesel exhausts have a drastic effect on the bee's sense of smell, thereby hampering its foraging activity.

The research, led by Dr. Tracey Newman and Professor Guy Poppy at the University of Southampton, claims that exposure to common air pollutants present in diesel exhaust can hinder the honeybees' ability to identify floral odors. This hampers their foraging efficiency as the bees depend on their sense of smell to locate, identify and recognize flowers.

Diesel exhaust that is known for its characteristic smell, contains fine toxic air contaminants. In the previous decade, it was believed that diesel exhaust made up a quarter of the air pollution. The exhaust gases have the capacity to alter the profile of a flora odor.

The researchers fear that if this trend continues, the diesel fumes will affect the insect's foraging activity, pollination and global food security. Compared to fruit flies or mosquitoes,  honeybees have a much better sense of smell. Studies say that honeybees have 170 odorant receptors and this augments the olfactory abilities of honeybees as they highly depend on odor recognition for food. Odorant receptors apart from helping find food allow the bees to communicate locations to other bees. The bees don't really have to rely on their gustatory receptors for taste as they can complete their foraging activity based on their strong olfactory sense.

The researchers conducted an experiment in which they produced a synthetic floral odor from a blend of eight chemicals similar to the one found in oilseed rape flowers. The smell was then introduced into a few glass containers. A few of these glass containers were then exposed to different concentrations of air with diesel fumes. After a gap of two hours the researchers measured the concentrations of the chemicals under different conditions. They noticed six out of the eight chemicals dropped in volume when combined with diesel exhaust and two other chemicals vanished completely within a minute. This indicated that the profile of the chemical mix had altered completely. The glass containers that were mixed with clean air remained unchanged.

When the researchers repeated the same experiment with nitric oxide and nitrogen dioxide they discovered the same result, suggesting that nitric oxide and nitrogen dioxide, contaminants in diesel exhaust, are the key facilitators in altering the odor's profile. Honeybees were later introduced to the same chemical mix of synthetic floral odor along with nectar. And these bees were later put in test chambers to check if contamination hampered their sense of smell. They decided this on the basis of whether the bees extended their proboscis (mouth part from where they suck the nectar). If the insects did not extend the proboscis, it clearly indicated their loss of sense of smell. The researchers noted that the bees extended their proboscis within 10 seconds in the contaminated air, NBCNews reports.

The bees failed to recognize the chemical mix.

Honeybees increase the yield of crops. But for this they need to forage effectively. The presence of nitrogen oxides disrupts the odor recognition that these bees rely on.

Professor Poppy, an ecologist at the University explains,".....Honeybees use the whole range of chemicals found in a floral blend to discriminate between different blends, and the results suggest that some chemicals in a blend may be more important than other"

Dr Newman, a neuroscientist at the University concludes, "Honeybees have a sensitive sense of smell and an exceptional ability to learn and memorize new odours. NOx gases represent some of the most reactive gases produced from diesel combustion and other fossil fuels, but the emissions limits for nitrogen dioxide are regularly exceeded, especially in urban areas. Our results suggest that that diesel exhaust pollution alters the components of a synthetic floral odour blend, which affects the honeybee's recognition of the odour. This could have serious detrimental effects on the number of honeybee colonies and pollination activity."