Plummeting insect numbers 'threaten collapse of nature'
Insects
Exclusive: Insects could vanish within a century at current
rate of decline, says global review
Why are insects in decline, and can we do anything about it?
Damian Carrington Environment editor
@dpcarrington
Sun 10 Feb 2019 18.00 GMT Last modified on Mon 11 Feb 2019
01.00 GMT
The rate of insect extinction is eight times faster than
that of mammals, birds and reptiles.
The rate of insect
extinction is eight times faster than that of mammals, birds and reptiles.
Photograph: Courtesy of Entomologisher Verein Krefeld
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.
The planet is at the start of a sixth mass extinction in its
history, with huge losses already reported in larger animals that are easier to
study. But insects are by far the most varied and abundant animals, outweighing
humanity by 17 times. They are “essential” for the proper functioning of all
ecosystems, the researchers say, as food for other creatures, pollinators and
recyclers of nutrients.
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.”
The analysis, published in the journal Biological
Conservation, says intensive agriculture is the main driver of the declines,
particularly the heavy use of pesticides. Urbanisation and climate change are
also significant factors.
“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.
Bees have also been seriously affected, with only half of
the bumblebee species found in Oklahoma in the US in 1949 being present in
2013. The number of honeybee colonies in the US was 6 million in 1947, but 3.5
million have been lost since.
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.
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.”
Sem comentários:
Enviar um comentário