Diesel exhaust gases disturb the flower location of bees

Nitrogen oxides decompose important fragrance components for the detection

Car exhaust © BMU / H.-G. Oed
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Honeybees do not have it easy: in many regions, monocultures are running low on food, they are poisoned by pesticides and mites parasitize them and their brood. Now researchers have discovered another problem: Diesel exhaust makes it difficult for the yellow-black insects to find flowers. Because especially the nitrogen oxides in the exhaust decompose and change the flower scent so that the bees can no longer locate the flowers. This could have serious consequences for these important pollinators, the researchers warn in the journal "Scientific Reports".

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Honey bees are eye and nose animals: From a distance, they are usually first guided by optical signals - the color and shape of a flower. Once they reach it, the smell comes into play: the bee registers the characteristic mix of chemicals that make up the fragrance of the flower and learns to associate it with its reward - the nectar and pollen. "Honeybees have a very sensitive sense of smell and an extraordinary ability to learn and retain new fragrances, " explains Tracey Newman of the University of Southampton, one of the two study leaders. Once the bee has noticed the fragrance cocktail of a flower variety, it uses it to track worthwhile flowers, even from a distance.

But what if something disturbs this fragrance location? This question was also asked by Newman and her colleagues. Their suspicion: The air pollution - and especially the exhaust gases of diesel vehicles - could disrupt the chemical orientation of the bees. "Air pollution is one of the most pervasive environmental influences of humans, " said the researchers. Despite catalytic converters and stricter emission standards, diesel exhaust is still one of the main components of air pollution. Above all, the nitrogen oxides contained in the exhaust are chemically very reactive. However, whether and how these emissions affect the honey bees and their fragrance location was previously unknown.

Fragrance components decomposed

In laboratory experiments, the researchers have now examined this more closely. For this they first built the typical scent cocktail of flowering rape from eight chemical compounds. They put this cocktail in two airtight containers and then introduced one of the two diesel exhaust gases. Using combined gas chromatography mass spectrometry, they subsequently determined the concentration of the eight fragrance components at regular intervals. The researchers carried out the same test with pure nitrogen oxides instead of diesel exhaust. display

The result: in both cases, two components of the rape fragrance decomposed after just a few minutes. "They were no longer detectable in the diesel exhaust-polluted air, " the scientists report. Two more connections also decreased a bit later. Since this was the same in the exhaust gases as in the approach with only the nitrogen oxides, the researchers conclude that the reactive nitrogen oxides in the diesel exhaust gases, in particular, cause this disintegration of the fragrance molecules.

Bee no longer recognizes the scent of flowers

But what does this mean for the bees? To test this, the researchers did the smell test. They exposed honeybees either to the unaltered synthetic rape fragrance or to fragrance mixtures that lacked the components decomposed by the exhaust gases and nitrogen oxides. Then they watched as the insects reached out their mouths - usually a typical reaction to the enticing scent of blossoms. In the unchanged mix, the bees reacted as expected. But not in the mixtures, which lacked one or more components. Apparently the honeybees did not recognize these mixtures as a flower signal, the researchers conclude.

"Our results indicate that diesel exhaust changes the composition of flower perfumes - and that this does not affect the honey bee's odor detection, " states Newman. However, as bees rely on this form of location for effective collection flights, this could have serious consequences for the bees and their survival, the researchers warn. Given the great importance that honeybees have for the Best ubung important crops, this is not a trifle. (Scientific Reports, 2013; doi: 10.1038 / srep02779)

(Scientific Reports, 04.10.2013 - NPO)