ＬＥＤ街灯で虫の個体数減少、産卵や摂食行動に影響か　英研究

【ワシントンＡＦＰ＝時事】街灯の昆虫への影響を調べた英国の研究で、特に白色発光ダイオード（ＬＥＤ）を使用した街灯が虫の行動パターンを乱すだけでなく、個体数減少の原因にもなっていることが分かったとする論文が２５日、発表された。（写真は英オックスフォードシャーで、ＬＥＤライトの街灯に照らされた交差点。ダグラス・ボーイズ氏提供）
　調査チームはイングランド南部で、街灯に照らされた道路沿いの生け垣や草地と、ほぼ同じ環境で街灯に照らされていない同数の地点を比較調査。また、植生が類似した街灯のない１区画と街灯のある２区画を調べた。
　調査対象としては、夜行性の昆虫の代替指標として、ふ化してから成虫になるまでの生息範囲が数メートル以内にとどまるガの幼虫を選んだ。
　調査結果は驚くべきもので、街灯に照らされた場所の幼虫の生息数は、街灯のない場所と比べて沿道の生け垣で４７％、沿道の草地では３７％少なかった。
　論文主執筆者で英生態学・水文学センター（ＵＫＣＥＨ）のダグラス・ボーイズ氏は、街灯のある場所では雌が産卵しないことが原因の可能性が高いとＡＦＰに語った。
　街灯は、ガの幼虫の摂食行動にも影響していた。街灯に照らされた場所にいる幼虫の体重は、街灯のない場所の幼虫より重かったが、研究チームは幼虫が数百万年に及ぶ進化で適応してきた生息条件と相反する不慣れな環境に適応できず、成長を急ぐあまり食べ過ぎているためだとみている。
　幼虫の摂食行動の乱れは、日光に近い黄色やオレンジ色の光を発する高圧ナトリウム（ＨＰＳ）ランプや低圧ナトリウム（ＬＰＳ）ランプより、ＬＥＤライトが当たる場所で顕著だった。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2021/08/27-12:10）

Streetlights -- particularly 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.
Artificial lights at night had been identified as a possible factor behind falling insect populations around the world, but the topic had been under-researched.
To address the question, scientists compared 26 roadside sites consisting of either hedgerows or grass verges that were lit by streetlights, against an equal number of nearly identical sites that were unlit.
They also examined a site with one unlit and two lit sections, all of which were similar in their vegetation.
The team chose moth caterpillars as a proxy for nocturnal insects more broadly, because they remain within a few meters of where they hatched during the larval stage of their lives, before they acquire the ability to fly.
The team either struck the hedges with sticks so that the caterpillars fell out, or swept the grass with nets to pick them up.
The results were eye-opening, with a 47 percent reduction in insect population at the hedgerow sites and 37 percent reduction at the roadside grassy areas.
We were really quite taken aback by just how stark it was, lead author Douglas Boyes, of the UK Centre for Ecology and Hydrology, told AFP, adding the team had expected a more modest decline of around 10 percent.
We consider it most likely that it's due to females, mums, not laying eggs in these areas, he said.
The lighting also disturbed their feeding behavior: when the team weighed the caterpillars, they found that those in the lighted areas were heavier.
Boyes said the team interpreted that as the caterpillars not knowing how to respond to the unfamiliar situation that runs counter to the conditions they evolved in over millions of years, and feeding more as a result to rush through their development.
The team found that the disruption was most pronounced in areas lit by LED lights as opposed to high-pressure sodium (HPS) lamps or older low-pressure sodium (LPS) lamps, both of which produce a yellow-orange glow that is less like sunlight.
LED lamps have grown more popular in recent years because of their superior energy efficiency.
The paper acknowledged the effect of street lighting is localized and a minor contributor to declining insect numbers, with other important factors including urbanization and destruction of their habitats, intensive agriculture, pollution and climate change.
But even localized reductions can have cascading consequences for the wider ecosystem, resulting in less food for the birds and bats that prey upon insects.
Moreover, there are really quite accessible solutions, said Boyes -- like applying filters to change the lamps' color, or adding shields so that the light shines only on the road, not insect habitats.