“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