“This could explain why insecticides are more
effective some times than other times.” — NANCY MORAN
Bugs join forces against pesticide
By Devin Powell
Insects and microbes have teamed up
against a pesticide commonly sprayed on
crops. In lab tests, swallowing a bellyful
of certain bacteria protected bugs from
the toxic chemical.
This detoxifying diet is the first example of a symbiotic relationship that provides insecticide resistance, scientists
report online April 23 in the Proceedings
of the National Academy of Sciences.
“Mechanisms of insecticide resis-
tance have been thought to be encoded
by the insect genomes themselves,” says
Yoshitomo Kikuchi, a microbiologist
at the National Institute of Advanced
Industrial Science and Technology in
Hokkaido, Japan. “Our findings overturn
the common sense.”
Kikuchi and his colleagues treated
pots of soil with fenitrothion, a cheap in-
secticide used worldwide. Burkholderia
bacteria, which can disarm the pesticide
and break it down for its carbon, flour-
ished in the dirt.
The insecticide-munching microbes
also thrived inside young bean bugs,
Riptortus pedestris, exposed to seedlings grown in the pots or fed the
bacteria by the researchers. A single
insect can support an estimated 100
million Burkholderia cells in its gut.
In return for providing a comfortable
living space, infected bean bugs acquired
a new tolerance to the pesticide in the
lab. Most of the insects survived doses
of fenitrothion that killed 80 percent
or more of their undefended comrades
within five days.
Some scientists worry that this resistance could spread quickly. Insecticide
resistance typically evolves slowly, as
genetic changes arise and spread in successive insect generations. Snatching up
soil bacteria, which reproduce quickly
and thus evolve much faster, seems an
The bean bug Riptortus pedestris, a
soybean pest, can acquire resistance to
the common insecticide fenitrothion by
nurturing protective bacteria in its gut.
easy shortcut. Insects flying from place
to place could also spread their microbial allies.
“This could explain why insecticides
are more effective some times than other
times,” says Nancy Moran, an evolution-
ary biologist at Yale University.
Puffs of methane
found over Arctic
Bacteria may be source of
unexplained gas emissions
in the May Nature Geoscience.
Methane-spewing bacteria that live in
Arctic surface waters are the prime suspects. But the new data call into question
understanding of these microbes, says
oceanographer David Karl of the University of Hawaii at Manoa. Normally, these
bacteria — in the guts of animals and elsewhere — thrive with no oxygen. But the
ocean surface is usually saturated with
oxygen. “This exciting study reminds us
how little we know about microbial processes in the sea,” Karl says.
Kort and colleagues calculate the Arctic’s daily methane emissions during the
flybys at about 2 milligrams per square
meter. “That’s a pretty significant flux to
come out of the ocean,” Kort says.
The big question for climate scientists
is how pervasive this seawater methane
is. If the measurements reflect the Arc-
tic’s marine emissions for much of the
year, Kort says, “this could be a pretty
substantial methane source.”
The winter methane spikes could be
explained by seasonal nutrient shifts that
favor methane-producing bacteria.
By Janet Raloff
Atmospheric scientist Eric Kort was flying over the Arctic Ocean three years ago,
monitoring readouts as onboard sensors
sniffed the air. Suddenly, as the plane
dipped low over some breaks in the sea’s
ice cover, those instruments detected the
unmistakable whiff of methane, the second most important climate-warming
gas associated with human activities.
“This was unexpected,” says Kort,
of NASA’s Jet Propulsion Laboratory
in Pasadena, Calif. On four more
excursions north of the Beaufort and
Chukchi seas through 2010 — all from
November to April — the plane’s sensors detected the same taint of methane
in low-altitude air over broken patches
of ice, Kort and collaborators report
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June 2, 2012 | SCIENCE NEWS | 9
