an Attackerof Saltcedar
In the search for the perfect attactrant for the biocontrol
beetle Diorhabda elongata, scientists used a technique called "electroantennographic
detection." To find out which scent attracts the beetle the most,
they hooked up an electrode to a beetle antenna on a severed beetle head
and measured electrical stimulation triggered in the antenna by the various
scents collected from other D. elongata beetles.
Monitoring an introduced leafbeetle's attacks on saltcedar could become an
easier task now that scientists have synthesized the beneficial insect's chemical
attractant, or pheromone.
Saltcedar (Tamarix)the beetle's favorite foodis an invasive
tree from Eurasia that's become established in 20-plus U.S. states, costing
$100 million annually in degraded wildlife habitat, increased soil salinity,
water quality and quantity problems, and other harm. The beetle, Diorhabda
elongata, is a natural enemy that's being tested in seven western states
as a biological control agent. (See "Beneficial
Beetles Take a Bite Out of Saltcedar" in this issue.)
Monitoring the beetle's spread outward from the release site is a key part
of ARS's biologically based integrated
weed-management approach. So say Robert Bartelt and Allard Cossé, entomologists
who identified and synthesized the beetle's pheromoneand saltcedar scents
that attract the insectin studies at ARS's National Center for Agricultural
Utilization Research, Peoria, Illinois.
It's very important to know how far, how quickly, and in what directions the
beetles move and how successful they might be in establishing new zones of infestation.
Currently, beetle monitoring requires a sharp eye, dexterity with a sweep net,
and a keen sense of direction while trekking through 12-foot-high thickets of
"This is where the pheromone and saltcedar scent come into play; they
help us detect beetles quickly and with great sensitivityfar better than
a guy with a butterfly net!" says Bartelt. Sticky traps baited with these
attractants are deployed in a range of saltcedar patches to determine whether
the beetles are moving in.
In the lab, Bartelt and Cossé began the attractant research by first
placing male or female beetles in a special glass tube containing a sprig of
saltcedar. Any scents emitted by the beetlesor chewed saltcedar leaveswere
collected for identification by a gas chromatograph-mass spectrometer. Compounds
emitted by just one sex were considered likely to be pheromone components.
Then, using a technique called "electroantennographic detection,"
the researchers measured electrical stimulation triggered in the antennae of
severed beetle heads by the various collected chemicals. Two male-specific compoundsan
alcohol and an aldehydewere readily detected by the antennae, as would
be expected for pheromones. From affordable, off-the-shelf chemicals, the researchers
then made a synthetic version of these compounds.
Field tests last year confirmed the compounds' potential. More tests are planned
as part of the ARS-led Saltcedar Biological Control Consortium.
The scientists used the same approach to synthesize saltcedar odors. Interestingly,
mixing these odors with the synthetic pheromone worked better than either used
alone. "We're now trying to improve the blend of these two scents,"
says Bartelt.By Jan
Suszkiw, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
Robert J. Bartelt and Allard
A. Cossé are in the USDA-ARS Crop Bioprotection Research Unit, National
Center for Agricultural Utilization Research, 1815 N. University Street,
Peoria, IL 61604; phone (309) 681-6237 [Bartelt], (309) 681-6217 [Cossé],
fax (309) 681-6693.
"Tracking an Attackerof Saltcedar"
was published in the April
2005 issue of Agricultural Research magazine.