ホタルの絶滅危機、光害や観光なども原因　研究

【パリＡＦＰ＝時事】ホタルの多くの種が、生息地の減少や人工光による公害、観光などが原因で絶滅の危機に直面しているとの研究結果が3日、米専門誌「バイオサイエンス」で発表された。世界のホタル種の現状に関する大規模調査は今回が初めて。（写真は求愛行動で光を出すツチボタルの雌。米タフツ大学提供）
　甲虫類の仲間であるホタルは２０００種以上存在し、世界各地の湿地、沼地、草原、森林、都市公園などを照らしている。
　だが、英イングランド南部に生息するツチボタル、一斉に点滅を繰り返すマレーシアのプテロプティックス・テナー、米アパラチア山脈のブルーゴーストなどさまざまなホタル種が、人間の活動範囲の拡大により絶滅の危機に追い込まれている。
　専門家らは、絶滅の要因として考えられる１０項目のうち、東アジアと南米を除く世界各地では、生息地の減少が最大の脅威となっていると指摘している。
　例えば、マレーシアのプテロプティックス・テナーは、幼虫の間は川辺のマングローブに生息している。だがマングローブ林の多くは、パーム油のプランテーションや養魚場をつくるために伐採されてしまった。
　一方、東アジアと南米では、人工光がホタルにとって最大の脅威とされている。
　論文の共同執筆者で、米タフツ大学博士課程学生のアバロン・オーエンス氏は「光害は自然のバイオリズムを乱すだけでなく、ホタルの求愛行動を台無しにしてしまう」と説明した。
　ホタル種の多くは、光ることによって繁殖相手にアピールしている。また、成虫である期間が限られていることが、問題をさらに深刻化させている。ホタルの幼虫期は数か月から数年続くが、成虫の寿命は通常わずか数日しかない。
　観光も脅威の一つだ。ホタルの光は、人々を魅了してやまず、日本、マレーシア、台湾ではホタル観賞が長年人気を集めている。だが、過剰な観光客の流入により脆弱（ぜいじゃく）な生態系が損なわれ、ホタルに大きな打撃を与えている。
　さらに今回の調査では、広く使用されている殺虫剤がホタルにとって３番目に大きな脅威となっていることも分かった。
　また、気候変動は今のところホタルへの脅威だと考えられていないが、将来、海面上昇や干ばつが起これば、絶滅を加速させる可能性がある。
　今回の研究に参加した１２人の論文執筆者は、２０１８年に設立された国際自然保護連合（ＩＵＣＮ）ホタル専門家部会に所属している。ＩＵＣＮは絶滅危惧種をまとめた「レッドリスト」を編さんしている。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/02/05-12:34）

Fireflies are in deep trouble, with many species facing extinction due to habitat loss and exposure to pesticides, according to the first major review of their global status, published Monday.
Adding irony to injury, one of Nature's most entrancing spectacles is also being snuffed out by artificial light pollution, researchers reported in the journal BioScience.
More than 2,000 species of fireflies -- which are, in fact, beetles -- illuminate wetlands, marshes, grasslands, forests and urban parks worldwide.
A few, such as the Big Dipper in the United States, seem to be flourishing.
Those guys can survive pretty much anywhere, said Sara Lewis, a biologist at Tufts University in Massachusetts and lead author of the study, based on a survey of dozens of firefly experts.
But other varieties -- from the glowworms of southern England to Malaysia's synchronous fireflies and the Appalachian blue ghost, both of which draw tourists -- are being extinguished by humanity's ever-expanding ecological footprint.
Some species get hit especially hard by habitat loss because they need specific conditions to complete their life cycle, said Lewis.
The Malaysian firefly Pteroptyx tener, for example, lives during its larval phase in riverside mangroves, many of which have been ripped up to make way for palm oil plantations and fish farms.
The glowworm (L. noctiluca) has another problem -- females are flightless, which means that can't simply buzz off to a new location when their habitat is swallowed by a suburb, commercial crop or country road.
Other species of fireflies, which eat only during their larval phase, are dietary specialists, meaning they subsist on one or two kinds of snail, earthworm or other soft-bodied prey.
When fruit orchards in Mediterranean Spain are abandoned or give way to urbanisation, so too do the snails preferred by aptly named Lampyris iberica, leaving the firefly larva nothing to eat.
- 'Flashing through the gloom' -
Adult Pteroptyx in Malaysia, meanwhile, gather for nightly courtship displays in specific trees located along mangrove rivers. Many of those trees have been cut down.
Of 10 possible drivers of extinction, experts fingered habitat loss as the top threat everywhere -- except east Asia and South America.
In those two regions, artificial light was seen as the biggest menace to the world's luminescent beetles.
In addition to disrupting natural biorhythms, light pollution really messes up firefly mating rituals, said co-author Avalon Owens, a doctoral student at Tufts.
Many species of firefly depend on their ability to light up to find and attract mates.
To make matters worse, that window of opportunity is very narrow: while the firefly larval phase lasts months to years, adults typically live only a few days.
The twinkling beetles are so focused on reproducing that they don't even eat.
The survey found that fireflies are also being decimated by commonly used insecticides, the third major threat.
Organophosphates and neonicotinoids are designed to kill pests, yet they also have off-target effects on beneficial insects, the researchers wrote.
Fireflies light up by triggering a chemical reaction ?- involving oxygen, calcium and an enzyme called luciferase -- inside special organs in their abdomen, a process called bioluminescence.
Their otherworldly glow has been an enduring source of fascination.
But firefly tourism -- long popular in Japan, Malaysia and Taiwan -- has also taken a toll, with fragile ecosystems damaged by too much foot traffic.
The plight of fireflies at the beginning of the 21st century add a new layer of meaning to lines written more than a century ago by Canadian poet Bliss Carman.
And the fireflies across the dusk, Are flashing signals through the gloom, he wrote.
While climate change is not seen as a current threat, future sea level rise and drought also could accelerate the drive towards extinction.
The dozen authors contributing to the study are all affiliated with the Firefly Specialist Group -- set up in 2018 -- of the International Union for the Conservation of Nature (IUCN), which compiles the Red List of threatened species.