Lighting Stunts Aphids’ Edibles
A long-term, ongoing study reveals that artificial nighttime light sources – such as street lamps – can have an impact on the natural environment in ways that are complicated and difficult to predict. Researchers at the University of Exeter’s Environmental and Sustainability Institute (ESI) in Penryn, England, published their work in the journal Philosophical Transactions of the Royal Society B (doi: 10.1098/rstb.2014.0131).
“Our results suggest that by lighting up our nighttime environment, we trigger complex effects on natural food webs,” said Dr. Jonathan Bennie, part of the ESI team. “While we are all aware that street lights often attract insects at night, we show that they have more permanent, widespread impacts on wildlife and ecosystems.”
An ongoing investigation on the effects of street lighting on artificial grassland communities has shown that ’amber’ lighting, simulating a commonly used type of sodium street lamp, affects the food source of pea aphids, causing a decline in the population of the insect. Photo courtesy of Jon Bennie, University of Exeter.
In July 2012, Bennie and his colleagues set up 54 experimental mesocosms outdoors: a diversity of artificial grassland communities housed in transparent box-like structures. The team used the artificial ecosystems to study the population density of the pea aphid, a grassland insect, under two types of low-level lighting and various other conditions, such as the presence or absence of predatory ladybugs. The flowering shoots of a wild-growing legume, known as Greater Bird’s-foot Trefoil, is the aphids’ main food source. The legume was also transplanted to the man-made communities.
The researchers selectively applied a cool white light similar to commercial LED street lighting to the mesocosms. They also applied amber lighting to simulate low-pressure sodium lighting, another common form of street lighting. Downward-facing LEDs were mounted across the top of the mesocosms to supply the light treatments, which were switched on at sunset and off at sunrise by light-detecting photocells. Unlit mesocosms served as control treatments.
Over time, the investigators found that the low-intensity amber light inhibited the growth of the legumes’ flowering shoots. The researchers observed that the number of aphids was significantly lower under the amber light treatment during mid-August – the team attributed this to the decrease in the food source.
“This is the first time that the effects of artificial nighttime lighting on plants have been shown in turn to influence the organisms that feed on them,” said Kevin Gaston, director of ESI, who has studied the ecological impacts of urbanization for many years. “These kinds of cascading effects are probably very widespread but are challenging to disentangle.”
The team also found that the effects from the white light treatments were intermediate between those of the amber and the control treatments.
As for the challenges involved, Gaston noted that the experiments were very demanding, requiring a lot of time and effort to sustain and collect data. These are the first findings from major, long-term experiments funded by the European Research Council, he said.
“We are particularly interested to determine how the impacts of nighttime lighting might change as the experiment runs for longer. It seems likely that initial impacts will cause further cascades of subsequent effects.”
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