Diesel Exhaust Masks Odors Honeybees Use to Forage and Pollinate

Exhaust from diesel engines has been shown to prevent honeybees from differentiating between the odors of flowers, according to new research from the University of Southampton.

Honeybees rely on floral odors to locate and identify the flowers they collect pollen from, but when the aroma of diesel exhaust fumes is present the odor profile of surround flora is masked.

University of Southampton researchers Tracey Newman and Guy Poppy suggest that such odor masking prevents the bees from recognizing odors vital to their survival. Because bees' pollination endeavors are vital to the food system, the researchers contend that contamination of flora odors may affect honeybees' foraging efficiency, which could in turn affect pollination levels, which could harm global food security.

"Honeybee pollination can significantly increase the yield of crops and they are vital to the world's economy -- £430 million a year to the UK alone. However to forage effectively they need to be able to learn and recognize the plants," Poppy said.

The researchers set up an experiment which mixed eight chemicals found in the odor of oil in rapeseed flowers with clean air and air containing diesel exhaust. The odors of two of the chemicals disappeared completely when mixed with diesel exhaust air, and the other six reduced in volume. The odors mixed with clean air were unaffected.

When the same experiment was performed with nitric oxide and nitrogen dioxide (gasses found in diesel exhaust, referred to as NOx gasses), the same results occurred, which suggests that the gasses are key facilitators in how and why the floral odor's profile was affected.

"Honeybees have a sensitive sense of smell and an exceptional ability to learn and memorize new odors," Newman said. "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 odor blend, which affects the honeybee's recognition of the odor. This could have serious detrimental effects on the number of honeybee colonies and pollination activity."

Poppy added: "The results indicate that NOx gases -- particularly nitrogen dioxide -- may be capable of disrupting the odor recognition process that honeybees rely on for locating floral food resources. 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 others."

The researchers' work is published in the journal Scientific Reports.