From xxxxxx <[email protected]>
Subject 'The Insect Apocalypse' and How We Can Stop It
Date November 23, 2019 2:47 AM
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[Scientists say bug deaths can be cut by switching off unnecessary
lights] [[link removed]]

'THE INSECT APOCALYPSE' AND HOW WE CAN STOP IT  
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Damian Carrington
November 22, 2019
The Guardian
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_ Scientists say bug deaths can be cut by switching off unnecessary
lights _

Thousands of moths swarm around floodlights. Artificial light at
night can affect every aspect of insects’ lives, the researchers
said, Simone De Peak/Getty Images

 

Light pollution is a significant but overlooked driver of the rapid
decline of insect populations, according to the most comprehensive
review of the scientific evidence to date.

Artificial light at night can affect every aspect of insects’ lives,
the researchers said, from luring moths to their deaths around bulbs,
to spotlighting insect prey for rats and toads, to obscuring the
mating signals of fireflies.

“We strongly believe artificial light at night – in combination
with habitat loss, chemical pollution, invasive species, and climate
change – is driving insect declines,” the scientists concluded
after assessing more than 150 studies. “We posit here that
artificial light at night is another important – but often
overlooked – bringer of the insect apocalypse.”

Light pollution affects dung beetles, which use starlight to navigate.
“For us, light pollution is a shame as we can’t see the night
stars, but for a beetle it is literally life and death,” said Brett
Seymoure.

However, unlike other drivers of decline, light pollution was
relatively easy to prevent, the team said, by switching off
unnecessary lights and using proper shades. “Doing so could greatly
reduce insect losses immediately,” they said.

Brett Seymoure, a behavioural ecologist at Washington University in St
Louis and senior author of the review, said: “Artificial light at
night is human-caused lighting – ranging from streetlights to gas
flares from oil extraction. It can affect insects in pretty much every
imaginable part of their lives.”

[A dung beetle pushing a ball at night.]
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 A dung beetle pushing a ball at night. Photograph: National
Geographic Image Collection/Alamy Stock Photo

Insect population collapses have been reported in Germany
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Rico
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and the first global scientific review
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published in February, said widespread declines threatened to cause a
“catastrophic collapse of nature’s ecosystems”.

The latest review says: “Insects around the world are rapidly
declining. Their absence would have devastating consequences for life
on this planet.”

There are thought to be millions of insect species, most still unknown
to science, and about half are nocturnal. Those active in the day may
also be disturbed by light at night when they are at rest.

The corn earworm moth stops mating if light levels are above the
illumination provided by a quarter moon at night.

The analysis, published in the journal Biological Conservation
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notes that light has long been used deliberately by farmers to
suppress insects. But as human infrastructure has expanded, and the
cost of lighting has fallen, light pollution has come to affect a
quarter of the world’s land surface.

The most familiar impact of light pollution is moths flapping around a
bulb, mistaking it for the moon. One-third of insects trapped in the
orbit of such lights die before morning, according to work cited in
the review, either through exhaustion or being eaten.

[A privet hawkmoth in flight at night in Hungary]
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 A privet hawk moth in flight at night in Hungary Photograph:
Blickwinkel/Alamy

Recent research in the UK found greater losses of moths at
light-polluted sites than dark ones. Vehicle headlights pose a deadly
moving hazard, and this fatal attraction has been estimated to result
in 100 billion insect deaths per summer in Germany.

Artificial light also hinders insects finding a mate in some species,
the review found, most obviously in firefly beetles, which exchange
bioluminescent signals during courtship.

Some fruit flies emerge from their eggs before dawn when the
temperature and humidity is just right, but artificial light can
interfere with this.

Some insects use the polarisation of light to find the water they need
to breed, as light waves line up after reflecting from a smooth
surface. But artificial light can scupper this. “Mayflies live for
only one day, so they come out and look for polarised light. They find
it – but from asphalt – lay their eggs there, and they all die.
That’s a good way to knock out an entire population in 24 hours.”

The development of juvenile insects, such as field crickets, also has
been shown to be affected by light pollution, which changes the
perceived length of the day and night.

The review found the search for food is affected by light
pollution. Insects
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for example weta, the giant flightless crickets found in New Zealand,
spend less time foraging in light-polluted areas.

Insects are important prey for many species, but light pollution can
tip the balance in favour of the predator if it traps insects around
lights. Spiders, bats, rats, shorebirds, geckos and cane toads have
all been found feeding around artificial lights. Such increases in
predation risk was likely to cause the rapid extinction of affected
species, the researchers said.

Some fruit flies emerge from their eggs before dawn when the
temperature and humidity is just right, but artificial light can
interfere with this.

The researchers said light pollution is particularly hard for insects
to deal with. Most human-caused threats to insects have natural
analogues, such as climate change and invasive species, meaning some
adaptation may take place. But the daily cycle of light and dark had
remained constant for all of evolutionary time, they said.

However, light pollution was the easiest of all the threats to insects
to deal with, Seymoure said. “Once you turn off a light, it is gone.
You don’t have to go and clean up, like you do with most pollutants.
I am not saying we need to get rid of light at night, I think we just
need to use it wisely.”

[Thousands of dancing fireflies in Japan.]
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 Thousands of dancing fireflies in Japan. Photograph: Kei
Nomiyama/Barcroft Images

Simply turning off lights that are not needed is the most obvious
action, he said, while making lights motion-activated also cuts light
pollution. Shading lights so only the area needed is illuminated is
important, as is avoiding blue-white lights, which interfere with
daily rhythms. LED lights also offer hope as they can be easily tuned
to avoid harmful colours and flicker rates.

Warning colours that deter deter predators, such as those
of _Heliconius_ butterflies, can be obscured by light pollution,
while unnatural colours of light have been shown to prevent parasitic
wasps finding their victims.

“The evidence that light pollution has profound and serious impacts
on ecosystems is overwhelmingly strong,” said Matt Shardlow, the
chief executive of the conservation charity Buglife. “It is
imperative that society now takes substantial steps to make the
environment safer for insects.

“A national light-reduction target, enforceable in law, would be the
most appropriate next step.” He said new UK government
light-pollution guidance failed to take into account the insect
decline crisis.

Prof Nigel Raine, a pollination expert at Guelph University in Canada
who is not involved in the review, said: “Light pollution could have
significant ramifications at the insect population, species or
community level.”

He said more attention should be paid to the issue by scientists:
“But it might be too soon to say the impacts are as significant as
other stressors.”

Seymoure’s team said there had not been more research on light
pollution and insects because of diurnal bias – a preference among
ecologists for studying daytime phenomena.

_Damian Carrington is Environment editor of The Guardian.
@dpcarrington_

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