How sweet it isn't: Some cockroaches
evolve to avoid poison in just 5
years
NEW YORK (AP) — People have been
getting rid of cockroaches for decades
by setting out bait mixed with poison.
But in the late 1980s, in an apartment
test kitchen in Florida, something went
very wrong.
A killer product stopped working.
Cockroach populations there kept
rising. Mystified researchers tested
and discarded theory after theory
until they finally hit on the
explanation: In a remarkably rapid
display of evolution at work, many of
the cockroaches had lost their sweet
tooth, rejecting the corn syrup meant
to attract them.
In as little as five years, the sugar-
rejecting trait had become so
widespread that the bait had been
rendered useless.
"Cockroaches are highly adaptive, and
they're doing pretty well in the arms
race with us," said North Carolina
State University entomologist Jules
Silverman, discoverer of the glucose
aversion in that Florida kitchen during
a bait test.
The findings illustrate the evolutionary
prowess that has helped make
cockroaches so hard to stamp out that
it is jokingly suggested they could
survive nuclear war.
In a study published Thursday in the
journal Science, Silverman and other
researchers explain the workings of
the genetic mutation that gave some
roaches a competitive advantage that
enabled them to survive and multiply.
The key is certain neurons that signal
the brain about foods.
In normal cockroaches, glucose excites
neurons that tell the brain "Sweet!" In
the mutant insects, glucose activates
neurons that say "Sweet!" and ones
that say "Yuck!" The "Yuck!" neurons
dampen the signal from the others, so
the brain gets the message the taste is
awful. This unusual nerve activity
appeared in glucose-hating
cockroaches collected from Puerto
Rico as well as descendants of the
Florida insects.
The research focused on the German
cockroach, a small kind that can hitch
a ride into your home in a grocery bag,
not that big lunk known as the
American cockroach. Such finicky
eating habits have also been seen in
these smaller roaches in Southern
California, Cincinnati, Indiana, South
Korea and Russia.
Scientists are now
looking to see if other kinds of
cockroaches show aversion to glucose.
The new work is nifty science. But does
it explain why you can't get rid of the
little buggers in your kitchen?
Probably not, said Coby Schal, another
study author at North Carolina State.
Tests show that the glucose-hating
cockroaches are happy to eat most
types of bait these days, suggesting
that manufacturers have removed the
glucose or masked it, he said. (Bait
ingredients are a trade secret.) What's
more, the researchers found glucose-
hating cockroaches in only seven of 19
populations they sampled from
various locations.
Frankly, if the bait you put out isn't
working, it's probably because you're
using it incorrectly, suggested Schal,
who said he consults to the pesticide
industry free of charge.
Still, he said, the new work has
potential to help many consumers. By
studying how cockroaches evolve to
evade our poisons, scientists may find
clues to designing bait that the pests
cannot resist.
It's not clear when the Florida
cockroaches first encountered bait
with glucose or how quickly they
ditched their taste for the sugar, he
said. But he said it's reasonable to
estimate that it took maybe only five
years for that glucose aversion to
spread to so many cockroaches that
the bait was no longer effective. That's
about 25 generations of German
cockroaches, which can reproduce
about one to three months after
they're born, Schal said.
The glucose aversion may have arisen
in an individual cockroach in response
to bait. Or it may have already been
present in just a few individuals when
the arrival of the bait suddenly gave
them an advantage for surviving and
reproducing. Their offspring would
inherit the trait and increasingly
replace other cockroaches.
Michael Scharf, an entomologist at
Purdue University who studies urban
pests but wasn't involved in the new
work, noted that since the 1950s,
cockroaches have shown they can also
evolve resistance to insecticides. He
agreed the latest results should help
scientists develop better products to
control roaches.
Science Daily
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