The recent decline in the population of bees and other pollinators because of pesticides, climate change, diseases, and other causes has raised alarms among those concerned about crop production and biodiversity. Now, another threat to pollination has been identified by a team of researchers in Switzerland: light pollution.

Scientists at the University of Bern’s Institute of Ecology and Evolution report that artificial light disrupts nocturnal pollination and leads to a reduction in the number of fruits produced by plants. Lead researcher Eva Knop said that nocturnal pollinators – especially moths and beetles – have been largely ignored in the discussion of the global pollinator crisis but that they play an important role. To assess the effect of artificial light on these nighttime visitors, she conducted an experiment comparing pollination activity in meadows illuminated by LED street lamps to activity in meadows without any nearby light sources. The researchers recorded almost 300 insect species visiting the flowers of about 60 plant species, but there were 62 percent fewer nocturnal pollination visits in the illuminated meadows.

The consequences for biodiversity and food production could be significant because a reduction in nocturnal pollination leads to a decline in fruit set and crop yield. In one experiment encompassing 10 meadows – half illuminated and half unlit – the researchers evaluated the nocturnal pollination visits to cabbage thistle (Cirsium oleraceum), a common plant pollinated by numerous species of insects during day and night. They discovered that the average number of fruits produced per plant was 13 percent lower at the illuminated meadows.

“The pollination during the day obviously cannot compensate for the losses in the night,” Knop said. The results of this research have inspired the scientists to urge that measures be taken to reduce light pollution.

“Reducing the amount of light used is certainly the most efficient and good approach,” Knop said. “In addition, one can improve the way lamps illuminate the environment by directing the light to only the places where it is needed as opposed to spreading light in all directions. Further, not all light colors have similar effects; for insects, light blue is thought to be particularly harmful.”


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