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Like people, cockroaches like to hang out together,
especially when they have nothing else to do. Now, researchers
know why. Gut bacteria pooped along with their feces emit
odours that the cockroaches find attractive. When those
bacteria are missing, cockroaches tend to go it alone,
researchers have discovered. Gut microbes in other organisms
may likewise influence behavior in ways we have yet to
appreciate.
―We don‘t know whether microbes are generally important
in mediating chemical communications, but my best guess is that
it‘s widespread,‖ says Angela Douglas, who studies microbes and
their animal hosts at Cornell University and was not involved
with the work. Eavesdropping on microbe-cockroach
conversations could lead to better ways to control this common
household pest.
Insects typically communicate using odours called
pheromones; those that attract males to females are well-studied.
Since the 1970s, entomologists have also known that so-called
aggregation pheromones encourage cock roaches to stick close to
one another. But researchers never could agree on what those
pheromones really are. Some suggested they were waxy
substances in the outer skin; others argued they were nitrogenrich
compounds in the feces; and a third group insisted that fatty
acids—building blocks for fat—were involved, although which
ones exactly was under debate.
Coby Schal, an entomologist at North Carolina State
University (NC State) in Raleigh wondered whether the
conflicting results meant that different cockroaches depend on
different aggregation chemicals because of variation in their
environments, food, or gut microbes. So Schal and his team,
including NC State entomologist Ayako Wada-Katsumata
sterilized German cockroaches, Blattella germanica, and raised
them in germ-free cages, so their feces would be germ-free.
Usually cockroaches are attracted to their neighbors‘ feces, but
they tended to avoid the germ-free stuff.
When Wada-Katsumata isolated feces bacteria and fed them
to the germ-free cockroaches, the roaches once again tended to
form groups. Sophisticated chemical analyses of normal roach
poop and germ-free poop showed that the latter lacked many of
the usual fatty acids that evaporate from the feces once it is
exposed to air; the researchers conclude these volatile fatty acids may be the missing aggregation pheromones. Synthetic
versions of these compounds also cause cockroaches to
aggregate.
This study explains how different studies in the past have
yielded different results,‖ Douglas says. ―It all depends on the
microorganisms. This may be why fatty acid advocates
couldn‘t agree on which fatty acids were important. Schal says
that other candidate aggregation substances, in high
concentrations, also seem to help bring the insects together, but
these bacteria-produced compounds are much more potent and
may be the most important drivers, Coby says.
Other researchers have shown that a specific microbe
hosted by desert locusts helps induce crowding behavior in that
species. And in 2012, researchers suggested that bacteria living
in hyenas' scent glands impart the odors that help these animals
tell kin from nonkin or pick out group members. There‘s the
potential for this to be widespread, Schal says.
May Berenbaum, an entomologist at the University of
Illinois, Urbana-Champaign, who was not involved with the
work agrees. "It has become abundantly clear that insects
partner with a tremendous diversity of microbial [associates]
bugs are bug-infested, as it were," she points out. And in
cockroaches, they "produce a beautiful story of biological
cooperation.".
And how about people? What we eat affects the bacteria in
our guts, which in turn can affect what we smell like. But
although the resulting foul body odour may deter contact,
there‘s no evidence the bacteria play a positive role in
communication among humans, Schal says.
Cockroaches‘ gut microbes may make the insects stick
together.
He is now studying whether every population of
cockroaches (even the ones living in your kitchen versus the
ones in your basement) makes its own special aggregation
pheromone. Schal and his colleagues hope to develop a
synthetic aggregation pheromone that works for all German
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cockroaches. Such a compound would help lure roaches to
insecticides, baits, and traps, Douglas says: If we can understand
the chemistry of cockroach aggregation and its plasticity better,
we can devise better strategies for control.
Source: www.sciencedaily.com
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