LED streetlights contribute to insect population declines: study

Although artificial lights at night have been suggested as a factor in the decline of insect populations all over the globe, the subject has been neglected.
Streetlightsparticularly those that use white light-emitting diodes (LEDs)not only disrupt insect behavior but are also a culprit behind their declining numbers, a new study carried out in southern England showed Wednesday.

Although artificial lights at night have been suggested as a factor in the decline of insect populations all over the globe, the subject has been neglected.

Scientists compared 26 roadside locations that had either grass verges or hedgerows that were lit by streetlights to answer the question. They also compared them with nearly identical unlit sites.

They also looked at a site with two sections lit and one unlit, which all had similar vegetation.

Because they are only a few metres from the place they hatch during their larval stage, the team selected moth caterpillars to represent nocturnal insects in a more general way, they can be used as a proxy before they become able to fly.

The team either struck the hedges using sticks to knock out the caterpillars, or they swept the grass with nets in order to collect them.

These results were amazing, with a 47% reduction in the insect population at hedgerow sites and a 37% reduction at roadside grassy areas.

Douglas Boyes, lead author at the UK Centre for Ecology and Hydrology said that they were taken aback by the starkness of it. He added that the team had been expecting a smaller decline of about 10 percent.

Douglas Boyes provided this undated image. It shows a collection of moth caterpillars captured by sweep nets during fieldwork.

He said that it was most likely due to females, mothers, not laying eggs there.

Lighting also affected their feeding behavior. The team measured the caterpillars and found that the ones in the brighter areas were more heavy.

Boyes explained that the team took that to mean that the caterpillars were not able to adapt to a new environment that was different to what they had evolved in over millions years. They also fed more to speed up their development.

The disruption was more noticeable in areas that were lit with LED lights than high-pressure sodium lamps (HPS) or older low pressure sodium (LPS), which emit a yellow-orange glow less similar to sunlight.

Because of their high energy efficiency, LED lamps have become more popular in recent times.

The paper recognized that street lighting has a limited effect on declining insect numbers. Other important factors include urbanization, destruction of habitats, intensive farming, pollution, and climate change.

Even small reductions in one area can have a large impact on the ecosystem as a whole. This could lead to fewer insects for birds and bats.

Boyes said that there are "really quite accessible solutions" to this problem. He suggested adding filters to alter the color of the lamps or shields to ensure the light shines on roads and not in insect habitats.

Science Advances published the study.

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Further information: Street lighting can have detrimental effects on local insect populations. Science Advances, 25 August 2021: Vol. 7, no. 35, eabi8322, advances.sciencemag.org/content/7/35/eabi8322 Journal information: Science Advances Street lighting has detrimental impacts on local insect populations,, 25 Aug 2021: Vol. 7, no. 35, eabi8322, DOI: 10.1126/sciadv.abi8322

2021 AFP