Artificial light poses a threat to pollination

03 August 2017

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The use of artificial light at night, such as street lights, can harm pollination according to researchers at the University of Bern in Switzerland.

Pollinators are animals, commonly insects, that transfer pollen from plant to plant as they feed, allowing plants to reproduce.  More than 30% of our plant-based food supply depends on animal pollination, which had an estimated economic value of $361 billion in 2007.

Currently, a worldwide decline in pollinators threatens the security of global food production. This decline is due to human impact with factors such as habitat loss, pesticide use and climate change playing a role.

However, scientists are now turning their attentions to another impact that the human lifestyle may have on pollinator species - the use of artificial light during the night.

Pollinator species can be categorised based on their feeding times, with nocturnal pollinators only active during hours of darkness. However, the 24/7 nature of the human lifestyle, with activities such as night-shift work and socialising, means that it is necessary to keep streets well lit during these hours of darkness. Frequently, these light emissions from the city can also extend to neighbouring countryside and farmland.

Dr Eva Knop and colleagues wanted to know if artificial lighting has an effect on how these nocturnal pollinators behave and, consequently, how this affects fruit production of plants. To find out, 14 meadow sites were set up and half of them were subjected to artificial light at night. Armed with nets and night vision goggles, the team captured insects visiting each of the sites and compared the number of pollinators visiting artificially lit meadows to the number visiting the dark meadows. 

The results, published in Nature, show that sites subjected to artificial light during the night had a 62% reduction in the number of nocturnal pollinator visits compared to the unlit meadows. Furthermore, a 13% reduction in the fruit yield of a plant common to all meadows, the cabbage thistle, shows that daytime pollinators are unable to compensate for the negative effects of artificial light on their nocturnal counterparts.

With the use of artificial lighting spreading globally at a rate of 6% per year, Knop warns that “this new threat to pollinators will increase in the near future”. So what is the solution to this problem? Is it really feasible to turn out the lights after sundown?

Knop reassures that there is no need to plunge back into the dark ages just yet but adds that “it’s smart to take action now to mitigate the negative consequences of artificial light on pollination in the future”.

One potential solution involves altering the level of blue light emitted from street lights, as this is particularly detrimental to nocturnal pollinator behaviour. Alternatively, the use of motion-sensitive lights which are only activated in the presence of humans or cars passing by, would decrease overall light emissions and also reduce energy costs.

Switzerland is currently implementing such solutions and lighting the way for other countries to follow in their footsteps.
 

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