Plummeting insect numbers 'threaten collapse of nature'
Exclusive: Insects could vanish within a
century at current rate of decline, says global review
Damian Carrington, Environment editor, Guardian UK
Sun 10 Feb 2019 13.00 EST
The world’s insects are hurtling down the path to extinction,
threatening a “catastrophic collapse of nature’s ecosystems”,
according to the first global scientific review.
More than 40% of insect species are declining and a third are
endangered, the analysis found. The rate of extinction is eight
times faster than that of mammals, birds and reptiles. The total
mass of insects is falling by a precipitous 2.5% a year,
according to the best data available, suggesting they could
vanish within a century.
Insect population collapses have recently been reported in Germany
and Puerto Rico,
but the review strongly indicates the crisis is global. The
researchers set out their conclusions in unusually forceful terms
for a peer-reviewed scientific paper: “The [insect] trends confirm
that the sixth major extinction event is profoundly impacting [on]
life forms on our planet.
“Unless we change our ways of producing food, insects as a whole
will go down the path of extinction in a few decades,” they write.
“The repercussions this will have for the planet’s ecosystems are
catastrophic to say the least.”
Quick guide
Insect collapse: the red flags
Butterflies and moths
There has been a “severe
reduction” in butterflies and moths in the Kullaberg
Nature Reserve in Sweden compared to 50 years ago. Scientists
found over a quarter of the 600 species once found had been
lost. Butterflies were hardest hit, losing almost a half of
species, including the large tortoiseshell and scarce copper.
In England, two-thirds
of 340 moth species declined from 1968-2003.
Bumblebees
Museum records enabled scientists to assess the
fate of 16 species of bumblebees in the US midwest from
1900 to 2007. They found four had completely died out, while
eight were declining in number, and blamed intensive
agriculture and pesticides.
Dragonflies
Red dragonfly populations have fallen sharply in Japan since
the mid-1990s, which scientists link to insecticides in rice
paddies that stop the
water-living nymphs emerging into adults. In the US, recent
surveys across California and Nevada found 65% of
dragonflies and damselflies had declined in the 100 years
since 1914.
Leafhoppers
Leafhoppers and planthoppers often make up a large proportion
of the flying insects in European grasslands. But scientists
found their abundance in Germany plunged by
66% in the 50 years to 2010. Soil acidification, partly
due to heavy fertiliser use, was the main cause.
Ground beetles
In the UK, dramatic
declines in ground beetles have been seen in almost
three-quarters of the 68 carabid species studied from
1994-2008. A few species increased, but overall one in six of
all the beetles was lost in that time.
“If insect species losses cannot be halted, this will have
catastrophic consequences for both the planet’s ecosystems and for
the survival of mankind,” said Francisco Sánchez-Bayo, at the
University of Sydney, Australia, who wrote the review with Kris
Wyckhuys at the China Academy of Agricultural Sciences in Beijing.
The 2.5% rate of annual loss over the last 25-30 years is
“shocking”, Sánchez-Bayo told the Guardian: “It is very rapid. In
10 years you will have a quarter less, in 50 years only half left
and in 100 years you will have none.”
One of the biggest impacts of insect loss is on the many birds,
reptiles, amphibians and fish that eat insects. “If this food
source is taken away, all these animals starve to death,” he said.
Such cascading effects have already been seen in Puerto Rico,
where a recent study revealed a 98% fall in
ground insects over 35 years.
The new analysis selected the 73 best studies done to date to
assess the insect decline. Butterflies and moths are among the
worst hit. For example, the number of widespread butterfly species fell by 58% on
farmed land in England between 2000 and 2009. The UK has
suffered the biggest recorded insect falls overall, though that is
probably a result of being more intensely studied than most
places.
There are more than 350,000 species of beetle and many are
thought to have declined, especially dung beetles. But there are
also big gaps in knowledge, with very little known about many
flies, ants, aphids, shield bugs and crickets. Experts say there
is no reason to think they are faring any better than the studied
species.
A small number of adaptable species are increasing in number, but
not nearly enough to outweigh the big losses. “There are always
some species that take advantage of vacuum left by the extinction
of other species,” said Sanchez-Bayo. In the US, the common
eastern bumblebee is increasing due to its tolerance of
pesticides.
Most of the studies analysed were done in western Europe and the
US, with a few ranging from Australia to China and Brazil to South
Africa, but very few exist elsewhere.
“The main cause of the decline is agricultural intensification,”
Sánchez-Bayo said. “That means the elimination of all trees and
shrubs that normally surround the fields, so there are plain, bare
fields that are treated with synthetic fertilisers and
pesticides.” He said the demise of insects appears to have started
at the dawn of the 20th century, accelerated during the 1950s and
1960s and reached “alarming proportions” over the last two
decades.
He thinks new classes of insecticides introduced in the last 20
years, including neonicotinoids and fipronil, have been
particularly damaging as they are used routinely and persist in
the environment: “They sterilise the soil, killing all the grubs.”
This has effects even in nature reserves nearby; the 75% insect
losses recorded in Germany were in protected areas.
The world must change the way it produces food, Sánchez-Bayo
said, noting that organic farms
had more insects
and that occasional pesticide use in the past did not cause the
level of decline seen in recent decades. “Industrial-scale,
intensive agriculture is the one that is killing the ecosystems,”
he said.
In the tropics, where industrial agriculture is often not yet
present, the rising temperatures due to climate change are thought
to be a significant
factor in the decline. The species there have adapted to
very stable conditions and have little ability to change, as seen
in Puerto Rico.
Sánchez-Bayo said the unusually strong language used in the
review was not alarmist. “We wanted to really wake people up” and
the reviewers and editor agreed, he said. “When you consider 80%
of biomass of insects has disappeared in 25-30 years, it is a big
concern.”
Other scientists agree that it is becoming clear that insect
losses are now a serious global problem. “The evidence all points
in the same direction,” said Prof Dave Goulson at the University
of Sussex in the UK. “It should be of huge concern to all of us,
for insects are at the heart of every food web, they pollinate the
large majority of plant species, keep the soil healthy, recycle
nutrients, control pests, and much more. Love them or loathe them,
we humans cannot survive without insects.”
Matt Shardlow, at the conservation charity Buglife, said: “It is
gravely sobering to see this collation of evidence that
demonstrates the pitiful state of the world’s insect populations.
It is increasingly obvious that the planet’s ecology is breaking
and there is a need for an intense and global effort to halt and
reverse these dreadful trends.” In his opinion, the review
slightly overemphasises the role of pesticides and underplays
global warming, though other unstudied factors such as light
pollution might prove to be significant.
Prof Paul Ehrlich, at Stanford Universityin the US, has seen
insects vanish first-hand, through his work on checkerspot
butterflies on Stanford’s Jasper Ridge reserve. He first studied
them in 1960 but they had all
gone by 2000, largely due to climate change.
Ehrlich praised the review, saying: “It is extraordinary to have
gone through all those studies and analysed them as well as they
have.” He said the particularly large declines in aquatic insects
were striking. “But they don’t mention that it is human
overpopulation and overconsumption that is driving all the things
[eradicating insects], including climate change,” he said.
Sánchez-Bayo said he had recently witnessed an insect crash
himself. A recent family holiday involved a 400-mile (700km) drive
across rural Australia, but he had not once had to clean the
windscreen, he said. “Years ago you had to do this constantly.”
