As if global warming and climate change were not doing enough damage to pollinators and pollination around the world, a new threat has joined the league to make things more harsh for nocturnal pollinators.
A new study has found that light pollution – mostly through artificial lighting – during the night time affects night time pollination. Nocturnal pollination also helps greatly in food production, but this is now threatened by light pollution from artificial lights with scientists claiming that the loss of nocturnal pollination cannot be compensated through any means.
Researchers at the Institute of Ecology and Evolution at the University of Bern, show that artificial light is leading to a disruption of the pollination service provided by pollinators during the night time. Researchers found out that flowers on meadows which were experimentally illuminated with street lamps are visited around two thirds less frequently by pollinators, than those that were on meadows without any light sources in the vicinity.
Studies have indicated that over the course of last two decades, light emissions have increased by 70 per cent, particularly in residential areas. The researchers could show that during night a total of almost 300 insect species visited the flowers of around 60 plant species on ruderal meadows without any artificial light sources in the vicinity. Interestingly, on meadows with experimentally set up street lights, the nocturnal pollination visits were 62% lower than in the unlit areas. The LED lamps used, are used as standard for public street lighting.
Loss of nocturnal flower visitors leads to a reduction of the fruit set of plants, as the researchers have proved for the first time, with the example of the cabbage thistle (Cirsium oleraceum). The pale flower heads of the cabbage thistle are a rich and easily accessible source of pollen and nectar, for numerous species of insects, and are amongst the most visited plants both during the day and at night.
The team investigated a total of 100 cabbage thistles, which were growing on five meadows experimentally illuminated with LED street lamps, and five meadows without artificial light. The illuminated plants were visited much more rarely by pollinating insects at night, than the unlit plants.
The decline in pollinators had a significant influence on the reproduction of the cabbage thistles: at the end of the test phase, the average number of fruits per plants was around 13% lower.