Honeybees’ Ability to Recognize Floral Odors Thwarted by Diesel Exhaust

Diesel exhaust thwarts honeybee floral odor recognition1

A new study indicates that the honeybee population’s sense of floral odor may be thwarted by chemical constituents, released following the combustion of diesel fuel. It is thought that this recognition is key to the average honeybee successfully functioning within its environment.

Number of honey producing bee colonies
Number of honey producing bee colonies from 1945 to 2007 (Credit: U.S. Department of Agriculture’s National Agricultural Statistics Service

The honeybee (Apis mellifera) population is spiraling into a decline, presenting a potential global crisis. Four million honey bees were in existence 30 years ago; alas, this figure has decreased by over a half. Honeybees are one the world’s primary pollinators and are, therefore, a major component of agriculture, involved in the annual pollination of approximately $14 billion worth of crops in the United States alone. It is estimated that 70% of the world’s main food crops are reliant upon pollination for development.

A vast number of factors are theorized to influence honeybee population numbers. A report published by the United Nations Environment Programme (UNEP) suggested the following issues to explain their mysterious departure:

  • Exposure to pesticides
  • Bee-related pathologies (e.g. Varroa destructor, hive beetles)
  • Elevation in pollutants
  • Use of agricultural insecticides and herbicides
  • Destruction of natural ecosystems by humans

A team of Southampton researchers, situated in Britain, headed by Professor Guy Poppy and Dr. Tracey Newman have conducted new scientific research, providing credence to the theory that pollutants can seriously hamper honeybee function. Their findings were published in the Oct. 3 issue of the journal Scientific Reports.

Pollution and Pollination

Investigating the influence of diesel exhaust fumes, the team concluded that honeybees became confused by a disruption to “profiles of flora odor.” In turn, these aberrant changes lead to honeybees demonstrating a diminished capacity to forage, which could influence the rate of pollination.

Chemical odors are critical to an insect’s ability to effectively communicate and interact with their surroundings. To encourage pollination, plants release natural, floral odors; these chemical messengers trigger a  variety of insects to swarm to their location, enabling dissemination of pollen.

As air pollution is a ubiquitous product of human advancement, the authors decided to study its impact upon the sensitive smell reception of honeybees. A study by Lars Chittka and his colleagues, which explored flower constancy and insect psychology, found that the honeybees’ propensity towards pollination was affected by their sense of smell, as well as their ability to recall new odors.

What’s more, Quinn S. McFrederick and colleagues, working for the Department of Environmental Sciences, University of Virginia, explained how contaminants could influence the longevity of floral hydrocarbons within the atmosphere. McFrederick’s team claims pollutants (hydroxyl and nitrate radicals) can undergo a chemical reaction with these essential floral hydrocarbons, thereby interfering with pollen-mediated attraction.

NOx Gases and Disrupts Odor Recognition

The researchers acquired eight chemical constituents found to be released by rapeseed flowers, and combined them with different types of air – clean air, and diesel-contaminated air. All in all, the concentrations six of these chemical odors were found to have been reduced, when combined with polluted air; two of the chemicals disappeared after a single minute. In comparison, clean air failed to have any impact on the odor profile.

The group then began to contemplate chemical candidates, found in diesel, which could be responsible for changing the odor profile so radically. They then performed the exact same experiment, but used NOx gases (including nitric oxide and dioxide), which are released following combustion of diesel fuel. They found the exact same results, inferring that NOx gasses may have been responsible for the apparent chemical reaction, and the decline in floral odors.

In light of this new study, Dr. Newman, one of the university’s neuroscientists, explains the serious consequences of NOx gases:

“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.”

Meanwhile, the debate over exactly what is causing the honeybee decline still rages on. Although the prevailing theory revolves around a combination of factors, much scrutiny has

Neonicotinoids blamed for decline in honeybees
The relationship between neonicotinoid pesticides and the honeybee decline has been the source of much debate

focused upon the utility of neonicotinoid pesticides.

The European Food Safety Authority (EFSA) claims the link between neonicotinoids and the declining honeybee population to be significant and, amidst these fears, the European Union has banned the application of three of the major pesticides from this group. However, the British government argues the evidence to be highly inconclusive and urges caution when interpreting these scientific findings.

According to Reuters, Giles Budge, who is a member of Britain’s Food and Environment Research Agency, claimed that Newton’s research provided new insight into the problems facing the honeybee. However, he also recommended that further investigation be conducted outside of the laboratory to see if their findings are observed in the “wider environment.”

By: James Fenner

LV Guardian Express Link

Nature Scientific Reports Journal

Naturwissenschaften Journal Link

University of Southampton Press Release

Atmospheric Environment Journal

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