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Beetles tracked with ‘ray guns.’ dental floss
National Geographic News Scientists are combining space-age ray guns with dental floss to
get a read on how wood-boring beetles such as the Asian
longhorned beetle invade new countries.
“These pests have become a problem in the last 20 years or so
because of all the foreign trade.” said David Williams, an
entomologist with the U.S. Department of Agriculture’s Animal
and Plant Health Inspection Service in Cape Cod, Massachusetts.
The insects hitch rides across oceans in wooden crates and other
solid wood materials used in shipping, he explains. Once the
containers are unpacked, the insects fly off, mate, and spread.
The Asian longhorned beetle that invaded New York in 1996 has
since killed thousands of the state’s hardwood trees, including
maple, elms, willows, and poplars.
Williams’ primary responsibility is to study how to eradicate or
at least control invasive insects such as the Asian beetle.
Typically when an invader arrives, researchers identify its
location and search a wider circle around it for other bugs, he
says.
“In the case of wood-boring beetles, we’ll cut down all the host
trees that seem to be infested in an attempt to eradicate it,”
he said.
“What we need to know is how big the radius of the circle needs
to be—how far these bugs can fly.”Harmonic radar
Harmonic radar is one trick entomologists are using to
understand the range of large insects such as the Asian
longhorn.
The technique involves a transceiver, which Williams says looks
like a ray gun the fictional hero Buck Rogers might use, along
with tiny wire tags attached to the beetles.
The transceiver sends out a radar beam into the environment that
reflects off whatever it hits. Sensors then measure those
reflections.
But “everything out there is going to be received back at the
same frequency you send it out at...what you want is a unique
signal,” Williams said.
The tags attached to the beetles do this by reflecting back the
signal at a harmonic rate of frequency, at twice the frequency.
For example, if the transceiver sends out a signal at a
frequency of 917 megahertz, the tags will send back a signal at
1834 megahertz.
“That harmonic tag represents a unique signal out there from
everything else you’re looking at,” Williams said. “Attaching
that tag to an insect allows you to relocate the insect as it
flies around.”
In 2002 Williams and his colleagues went to the Asian longhorn
beetle’s native habitat of China and used harmonic radar
tracking to study the invasive bugs’ dispersal over a two-week
period.
Williams attached the tags with dental floss, because the bodies
of the 1.25–inch long (3.2–centimeter-long) shiny black beetles
are too waxy for glue to stick.
The team found that the beetles moved, on average, about 10 feet
(3 meters) per day.
Interestingly, most of the females were rather sedentary during
the study, Williams says.
He suspects that was because the study took place late in their
breeding cycle. One female, however, moved 100 feet (30 meters)
in a week.
While the findings have not modified the radii of circles
entomologists draw around there invasive pests, Williams said
the tracking study “gave is a basic idea of how quickly these
beetles can move on their own.
Basic biology
Doug Landis is an entomologist at Michigan Stare University in
East Lansing who has
examined the practicality of using harmonic radar to track
insects.
He said that for fairly large insects like the Asian longhorned
beetle, the technique allows scientists “to get a lot of
information that is simply inaccessible any other way.”
However, the tags that send the harmonic signal are most
effective when they have about three-inch-long
(eight-centimeter-long) antennas.
“So in tracing very small insects, it has its limits,” Landis
said.
Nevertheless, several studies, including Williams’ work with the
Asian longhorned beetles, have shown harmonic radar to be an
effective tracking tool to learn about the basic biology of
invasive species, he adds.
“That’s the basis of finding what their Achilles’ heel might
be.”
(reprinted with permission from The Maple News, Nov-Dec 2006)
A Female Asian Longhorned Beetle from the
University of Vermont’s web site
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