Tag Archives: odors

bee flowers

Air pollution confuses bees and hinders foraging

bee flowers

Credit: Pixabay

Bees have a very keen sense of smell — they need it in order to survive. Even thousands of feet from their original source, a bee can detect the odor molecules emitted by the various plants which it pollinates. But air pollution acts as a retardant, shortening the life span and travel distance of these odor molecules. As a result, bees become confused and now require more time to forage, a new study found.

“Many insects have nests that are up to 3,000 feet away from their food source, which means that scents need to travel long distances before insects can detect them,” said Jose D. Fuentes, professor of meteorology and atmospheric science, Penn State.

“Each insect has a detection threshold for certain kinds of scents and they find food by moving from areas of low concentrations of scents to areas of high concentrations.”

It’s common knowledge that plant emit volatile hydrocarbons in the atmosphere — these molecules create their pleasant smell. These chemicals interact with certain air pollutants like car exhaust sourced ozone — a chemical reaction which breaks down the plant odors. Moreover, this process leads to the creation of more pollutants like hydroxyl and nitrate radicals which amplify the feedback loop.

Penn State researchers sought to fully understand the chemical mechanisms involved in this interaction. Using a computer simulation, they first plotted changes in the concentration of flower odors as a result of air turbulence and chemical interactions. This model enabled a theoretical footing to track the scents’ concentrations and movements emitted by different flowers over time.

Some 90,000 simulations were run, in which bees’ foraging patterns were influenced by various scent levels, air pollution concentration and wind speed (a diluter).

As air pollution increases, scent lifetime and travel distance decrease in an inverse relationship. For instance, 60 parts per billion in ozone levels — the EPA’s threshold for “moderate” ozone pollution — was enough to confuse bees and hinder their ability to identify food. One scent molecule called alpha-pinene can survive up to 40 hours in an ozone free environment, but at 60 parts per billion (ppb) it only lasts ten hours. For 120 ppb, the dissipation time is only one hour.

The impact on the time it takes bees to forage was significant. It took 20 percent of bees ten minutes to sense the beta-caryophyllene odor in an ozone-free environment, but this timeframe quickly escalated to 180 minutes for only 20 ppb ozone.

“We found that when we confused the bees’ environment by modifying the gases present in the atmosphere, they spent more time foraging and would bring back less food, which would affect their colonies,” said Fuentes. “It’s similar to being asked to get a cup of coffee at the nearest cafeteria while you are blindfolded. It will be hard to locate the coffee shop without using visual cues. The same could happen to insect pollinators while foraging for food in polluted air masses.”

The findings bear a lot of significance for an already seriously threatened animal. The U.S. lost 42.1 percent of its bee colonies in just one year, between April 2014 and April 2015, owing to the dreaded colony collapse disorder, which is thought to be triggered by pesticide use.

“Honeybees and other pollinators are in trouble almost everywhere, and they pay us a lot of services through their pollination,” said Fuentes. “The more we can understand about what factors are affecting their decline in numbers, the more equipped we will be to intervene if needed.”




The human nose can distinguish over a trillion scents


A volunteer smelling a vial. Photo: Credit: Zach Veilleux / The Rockefeller University

There’s a common number thrown around for how many scents a human can smell – 10,000. Even scientific literature has cited this figure, though it is highly debatable. This makes a lot of people believe that they have an extremely poor sense of smell compared to most animals, like familiar canines. In reality, it seems humans may be able to smell more than one trillion different odors, debunking the myth that we humans have a nose only for a fraction of the molecules out there.

[ALSO READ] The uniqueness of smell: no two people smell the same

There’s a reason we can smell. It’s a fundamental sense that helps us distinguish between what foods are right to eat or not, sense danger and even find mates. There’s a sort of inferiority complex regarding our sense of smell. Ask most people on the street how they think their sense of smell is compared to animals, and they’ll tell you that we can smell oh so little. That may not be true, according to researchers at Rockefeller University in New York.

Going with your nose

The typical nose has 400 or so olfactory receptors, but that doesn’t mean they only bind to 400 molecules. Rather, these receptors work together to sense various mixes of molecules. For instance, the eye has only three eye receptors (the cones), yet people can see up to 10 million colours. It’s hard to distinguish a colour from another very similar one, but even though the nuances may by very subtle, your brain can still pick them up.

For the experiment, mixtures of 128 different scent molecules were created. Individually, the molecules resembled odors such as grass or citrus, but when they were all combined, the mix smelled unfamiliar. The team led by Leslie Vosshall, an olfaction researcher at the Rockefeller University in New York, asked volunteers to smell three vials containing three scents (two of one scent along with a third, different scent) and identify which of the three was unique. This process was repeated for more than 260 sets of vials.

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Based on how often the volunteers were able to identify the correct unique smell, an extrapolation was made to estimate how many scents an average person could distinguish out of all possible mixtures of 128 molecules. Their calculations suggests that an average person can distinguish from up to 1 trillion scents, but this figure could be much higher because there are more than 128 odor molecules.

Of course each person smells more or less better. The keenest sense of smell, based on previous research, is that of a non-smoking caucasion woman, in general.

Findings appeared in the journal Science.