[Pollinator] Where have all the insects gone?

[Matthew Shepherd]

FROM: Science magazine

http://www.sciencemag.org/news/2017/05/where-have-all-insects-gone



*Where have all the insects gone?*



By Gretchen Vogel

May. 10, 2017 , 9:00 AM



Entomologists call it the windshield phenomenon. "If you talk to people,
they have a gut feeling. They remember how insects used to smash on your
windscreen," says Wolfgang Wägele, director of the Leibniz Institute for
Animal Biodiversity in Bonn, Germany. Today, drivers spend less time
scraping and scrubbing. "I'm a very data-driven person," says Scott Black,
executive director of the Xerces Society for Invertebrate Conservation in
Portland, Oregon. "But it is a visceral reaction when you realize you don't
see that mess anymore."



Some people argue that cars today are more aerodynamic and therefore less
deadly to insects. But Black says his pride and joy as a teenager in
Nebraska was his 1969 Ford Mustang Mach 1—with some pretty sleek lines. "I
used to have to wash my car all the time. It was always covered with
insects." Lately, Martin Sorg, an entomologist here, has seen the opposite:
"I drive a Land Rover, with the aerodynamics of a refrigerator, and these
days it stays clean."



Though observations about splattered bugs aren't scientific, few reliable
data exist on the fate of important insect species. Scientists have tracked
alarming declines in domesticated honey bees, monarch butterflies, and
lightning bugs. But few have paid attention to the moths, hover flies,
beetles, and countless other insects that buzz and flitter through the warm
months. "We have a pretty good track record of ignoring most noncharismatic
species," which most insects are, says Joe Nocera, an ecologist at the
University of New Brunswick in Canada.



Of the scant records that do exist, many come from amateur naturalists,
whether butterfly collectors or bird watchers. Now, a new set of long-term
data is coming to light, this time from a dedicated group of mostly amateur
entomologists who have tracked insect abundance at more than 100 nature
reserves in western Europe since the 1980s.



Over that time the group, the Krefeld Entomological Society, has seen the
yearly insect catches fluctuate, as expected. But in 2013 they spotted
something alarming. When they returned to one of their earliest trapping
sites from 1989, the total mass of their catch had fallen by nearly 80%.
Perhaps it was a particularly bad year, they thought, so they set up the
traps again in 2014. The numbers were just as low. Through more direct
comparisons, the group—which had preserved thousands of samples over 3
decades—found dramatic declines across more than a dozen other sites.



Such losses reverberate up the food chain. "If you're an insect-eating bird
living in that area, four-fifths of your food is gone in the last
quarter-century, which is staggering," says Dave Goulson, an ecologist at
the University of Sussex in the United Kingdom, who is working with the
Krefeld group to analyze and publish some of the data. "One almost hopes
that it's not representative—that it's some strange artifact."



No one knows how broadly representative the data are of trends elsewhere.
But the specificity of the observations offers a unique window into the
state of some of the planet's less appreciated species. Germany's "Red
List" of endangered insects doesn't look alarming at first glance, says
Sorg, who curates the Krefeld society's extensive collection of insect
specimens. Few species are listed as extinct because they are still found
in one or two sites. But that obscures the fact that many have disappeared
from large areas where they were once common. Across Germany, only three
bumble bee species have vanished, but the Krefeld region has lost more than
half the two dozen bumble bee species that society members documented early
in the 20th century.



Members of the Krefeld society have been observing, recording, and
collecting insects from the region—and around the world—since 1905. Some of
the roughly 50 members—including teachers, telecommunication technicians,
and a book publisher—have become world experts on their favorite insects.
Siegfried Cymorek, for instance, who was active in the society from the
1950s through the 1980s, never completed high school. He was drafted into
the army as a teenager, and after the war he worked in the wood-protection
division at a local chemical plant. But because of his extensive knowledge
of wood-boring beetles, the Swiss Federal Institute of Technology in Zurich
awarded him an honorary doctorate in 1979. Over the years, members have
written more than 2000 publications on insect taxonomy, ecology, and
behavior.



The society's headquarters is a former school in the center of Krefeld, an
industrial town on the banks of the Rhine that was once famous for
producing silk. Disused classrooms store more than a million insect
specimens individually pinned and named in display cases. Most were
collected nearby, but some come from more exotic locales. Among them are
those from the collection of a local priest, an active member in the 1940s
and 1950s, who persuaded colleagues at mission stations around the world to
send him specimens. (The society's collection and archive are under
historical preservation protection.)



*Weighty disappearances*

Tens of millions more insects float in carefully labeled bottles of
alcohol—the yield from the society's monitoring projects in nature reserves
around the region. The reserves, set aside for their local ecological
value, are not pristine wilderness but "seminatural" habitats, such as
former hay meadows, full of wildflowers, birds, small mammals—and insects.
Some even include parts of agricultural fields, which farmers are free to
farm with conventional methods. Heinz Schwan, a retired chemist and
longtime society member who has weighed thousands of trap samples, says the
society began collecting long-term records of insect abundance partly by
chance. In the late 1970s and early 1980s, local authorities asked the
group for help evaluating how different strategies for managing the
reserves affected insect populations and diversity.



The members monitored each site only once every few years, but they set up
identical insect traps in the same place each time to ensure clean
comparisons. Because commercially available traps vary in ways that affect
the catch, the group makes their own. Named for the Swedish entomologist
René Malaise, who developed the basic design in the 1930s, each trap
resembles a floating tent. Black mesh fabric forms the base, topped by a
tent of white fabric and, at the summit, a collection container—a plastic
jar with an opening into another jar of alcohol. Insects trapped in the
fabric fly up to the jar, where the vapors gradually inebriate them and
they fall into the alcohol. The traps collect mainly species that fly a
meter or so above the ground. For people who worry that the traps
themselves might deplete insect populations, Sorg notes that each trap
catches just a few grams per day—equivalent to the daily diet of a shrew.



Sorg says society members saved all the samples because even in the 1980s
they recognized that each represented a snapshot of potentially intriguing
insect populations. "We found it fascinating—despite the fact that in 1982
the term ‘biodiversity' barely existed," he says. Many samples have not yet
been sorted and cataloged—a painstaking labor of love done with tweezers
and a microscope. Nor have the group's full findings been published. But
some of the data are emerging piecemeal in talks by society members and at
a hearing at the German Bundestag, the national parliament, and they are
unsettling.



Beyond the striking drop in overall insect biomass, the data point to
losses in overlooked groups for which almost no one has kept records. In
the Krefeld data, hover flies—important pollinators often mistaken for
bees—show a particularly steep decline. In 1989, the group's traps in one
reserve collected 17,291 hover flies from 143 species. In 2014, at the same
locations, they found only 2737 individuals from 104 species.



Since their initial findings in 2013, the group has installed more traps
each year. Working with researchers at several universities, society
members are looking for correlations with weather, changes in vegetation,
and other factors. No simple cause has yet emerged. Even in reserves where
plant diversity and abundance have improved, Sorg says, "the insect numbers
still plunged."



*A weather station for biodiversity*

Researchers in Germany hope to develop a set of automated sensors that will
monitor the abundance and diversity of plants, animals, and fungi with the
help of pattern recognition and DNA and chemical analysis.



Changes in land use surrounding the reserves are probably playing a role.
"We've lost huge amounts of habitat, which has certainly contributed to all
these declines," Goulson says. "If we turn all the seminatural habitats to
wheat and cornfields, then there will be virtually no life in those
fields." As fields expand and hedgerows disappear, the isolated islands of
habitat left can support fewer species. Increased fertilizer on remaining
grazing lands favors grasses over the diverse wildflowers that many insects
prefer. And when development replaces countryside, streets and buildings
generate light pollution that leads nocturnal insects astray and interrupts
their mating.



Neonicotinoid pesticides, already implicated in the widespread crash of bee
populations, are another prime suspect. Introduced in the 1980s, they are
now the world's most popular insecticides, initially viewed as relatively
benign because they are often applied directly to seeds rather than
sprayed. But because they are water soluble, they don't stay put in the
fields where they are used. Goulson and his colleagues reported in 2015
that nectar and pollen from wildflowers next to treated fields can have
higher concentrations of neonicotinoids than the crop plants. Although
initial safety studies showed that allowable levels of the compounds didn't
kill honey bees directly, they do affect the insects' abilities to navigate
and communicate, according to later research. Researchers found similar
effects in wild solitary bees and bumble bees.



Less is known about how those chemicals affect other insects, but new
studies of parasitoid wasps suggest those effects could be significant.
Those solitary wasps play multiple roles in ecosystems—as pollinators,
predators of other insects, and prey for larger animals. A team from the
University of Regensburg in Germany reported in *Scientific Reports* in
February that exposing the wasp *Nasonia vitripennis* to just 1 nanogram of
one common neonicotinoid cut mating rates by more than half and decreased
females' ability to find hosts. "It's as if the [exposed] insect is dead"
from a population point of view because it can't produce offspring, says
Lars Krogmann, an entomologist at the Stuttgart Natural History Museum in
Germany.



No one can prove that the pesticides are to blame for the decline, however.
"There is no data on insecticide levels, especially in nature reserves,"
Sorg says. The group has tried to find out what kinds of pesticides are
used in fields near the reserves, but that has proved difficult, he says.
"We simply don't know what the drivers are" in the Krefeld data, Goulson
says. "It's not an experiment. It's an observation of this massive decline.
The data themselves are strong. Understanding it and knowing what to do
about it is difficult."



The factors causing trouble for the hover flies, moths, and bumble bees in
Germany are probably at work elsewhere, if clean windshields are any
indication. Since 1968, scientists at Rothamsted Research, an agricultural
research center in Harpenden, U.K., have operated a system of suction
traps—12-meter-long suction tubes pointing skyward. Set up in fields to
monitor agricultural pests, the traps capture all manner of insects that
happen to fly over them; they are "effectively upside-down Hoovers running
24/7, continually sampling the air for migrating insects," says James Bell,
who heads the Rothamsted Insect Survey.



Between 1970 and 2002, the biomass caught in the traps in southern England
did not decline significantly. Catches in southern Scotland, however,
declined by more than two-thirds during the same period. Bell notes that
overall numbers in Scotland were much higher at the start of the study. "It
might be that much of the [insect] abundance in southern England had
already been lost" by 1970, he says, after the dramatic postwar changes in
agriculture and land use.



The stable catches in southern England are in part due to constant levels
of pests such as aphids, which can thrive when their insect predators are
removed. Such species can take advantage of a variety of environments, move
large distances, and reproduce multiple times per year. Some can even
benefit from pesticides because they reproduce quickly enough to develop
resistance, whereas their predators decline. "So lots of insects will do
great, but the insects that we love may not," Black says.



Other, more visible creatures may be feeling the effects of the insect
losses. Across North America and Europe, species of birds that eat flying
insects, such as larks, swallows, and swifts, are in steep decline. Habitat
loss certainly plays a role, Nocera says, "but the obvious factor that ties
them all together is their diet."



Some intriguing, although indirect, clues come from a rare ecological
treasure: decades' worth of stratified bird droppings. Nocera and his
colleagues have been probing disused chimneys across Canada in which
chimney swifts have built their nests for generations. From the droppings,
he and his colleagues can reconstruct the diets of the birds, which eat
almost exclusively insects caught on the wing.



The layers revealed a striking change in the birds' diets in the 1940s,
around the time DDT was introduced. The proportion of beetle remains
dropped off, suggesting the birds were eating smaller insects—and getting
fewer calories per catch. The proportion of beetle parts increased slightly
again after DDT was banned in the 1970s but never reached its earlier
levels. The lack of direct data on insect populations is frustrating,
Nocera says. "It's all correlative. We know that insect populations could
have changed to create the population decline we have now. But we don't
have the data, and we never will, because we can't go back in time."



Sorg and Wägele agree. "We deeply regret that we did not set up more traps
20 or 30 years ago," Sorg says. He and other Krefeld society members are
now working with Wägele's group to develop what they wish they had had
earlier: a system of automated monitoring stations they hope will combine
audio recordings, camera traps, pollen and spore filters, and automated
insect traps into a "biodiversity weather station". Instead of tedious
manual analysis, they hope to use automated sequencing and genetic
barcoding to analyze the insect samples. Such data could help pinpoint what
is causing the decline—and where efforts to reverse it might work best.



Paying attention to what E. O. Wilson calls "the little things that run the
world" is worthwhile, Sorg says. "We won't exterminate all insects. That's
nonsense. Vertebrates would die out first. But we can cause massive damage
to biodiversity—damage that harms us."
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