White Campion - AnemoneProjectors

Street lighting operating all night can alter the natural pollination of a common wildflower, a study involving Butterfly Conservation (BC) has revealed.

The research, published in the journal Ecosphere, found that the common wildflower White Campion was pollinated more successfully under full-night lighting than unlit controls or part-night lights. The results run counter to the research team’s previous findings and to a Swiss study that showed reduced nocturnal insect visits to alpine flowers and reduced pollination in a thistle species when lighting rigs were installed.

The study is the latest research from the collaboration between BC, Newcastle University and the Centre for Ecology & Hydrology which has previously demonstrated that nocturnal moths play more significant roles in plant pollination than had previously been thought and also that street lights may disrupt this important ecological function by luring moths upwards away from the flowers they could be pollinating.

White Campion is mainly pollinated at night by moths, although some pollination also takes place during the day by other insects, so the scientists predicted that pollination would be reduced in the presence of street lights.

To test this hypothesis, the researchers, led by Callum Macgregor (as part of his PhD research funded by NERC and BC), placed White Campion plants close to lighting rigs set up to mimic different types of street lights, and measured subsequent pollination.

The experiment enabled the scientists to test the impacts of various common street-lighting technologies, including high-pressure sodium and LED bulbs and full-night illumination versus lights being switched off late at night (as some councils are now doing with real street lights). By enclosing some of the Campion plants in insect-proof mesh during the day and others at night, they were also able to separate the effects of daytime and nocturnal pollination.

The results were unexpected. Pollination success was significantly higher for White Campion plants under full-night lighting than unlit controls or part-night lights.

Although the increased pollination of White Campion under full-night lighting is a benefit to the plant, it also shows disruption of the natural behaviour of insect pollinators. In this context, the part-night lighting regime seems preferable, as there was no difference in pollination rates between this and the unlit controls. Current moves by some local authorities to switch off street lights late at night may minimise ecological disruption as well as energy savings.

The reasons for the increase in pollination under full-night lighting require further investigation. It may be that moths are concentrated close to the street lights (due to their attraction to the light) and therefore there are more moths to pollinate the White Campion flowers.

If this is true then wildflowers growing away from street lights may suffer reduced pollination.

Another possibility is that the light makes the white flowers of the plant more visible to moths, which as a result leads to increasing pollination.

Richard Fox
Associate Director Recording & Research

Find out more about Butterfly Conservation’s scientific research

Macgregor, C.J., Pocock, M.J.O., Fox, R. & Evans, D.M. (2019). Effects of street lighting technologies on the success and quality of pollination in a nocturnally pollinated plant. Ecosphere 10, e02550.