Think of plant pollination and you probably think of bees, summer flowers and bright sunshine.

But nocturnal insects such as beetles and flies also play a key role in the process. A new study sheds light on a previously unknown problem for these lesser-known pollinators, namely artificial lighting.

Scientists working in Switzerland carried out an experiment in which they placed mobile streetlamps over plots of cabbage thistle.

Using night-vision goggles, they counted the visits of pollinating species to these experimental plots and compared them with plots left dark. What they found was that the lighted plots, compared with the dark ones, received far fewer visits from nocturnal pollinators (62 percent fewer) and that significantly fewer species were making the visits (29 percent fewer). Details of the study are in the latest issue of Nature, which writes:

"Illuminated thistles produced significantly fewer developed fruits than those in darkness. Plants covered in pollinator-proof bags, meanwhile, yielded the same relative number of fruits under artificial light and in the dark.""Even though daytime pollinators are usually more numerous than night-time pollinators, they were unable to make up the difference in lost pollination of plants kept under artificial lighting. This [could] be because some studies have shown that night-time pollinators seem to be more effective at transferring pollen between plants than their diurnal counterparts, says Eva Knop, an ecologist at the University of Bern in Switzerland and first author of the study. 'Thus, it is not just the quantity but also the quality that counts.'"

The research spotlights a potentially new twist to the pollinator crisis. Bee populations have fallen alarmingly in recent years, prompting fears about harm to plant species that are reliant on pollinators. The suppression of nocturnal pollinators due to artificial lighting could add to the problem.

However, there are caveats. The Nature article quotes U.K. ecologist and biogeographer Jon Sadler who says the intensity, direction and duration of artificial light also could affect plants and animals differently. Sadler also notes the possibility that while nocturnal pollinators avoid lighted areas, they might then concentrate in darker areas, increasing pollination there.

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