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In Search ofBiological Control
Agents for the Invasive Australian Pine
In a survey of the Australian countryside,
entomologist Gary Taylor (left) from the University of Adelaide and ARS
entomologist Greg Wheeler search for suitable biological control insects to be
tested for release in the United States to help control invasive Australian
pine.
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The Australian outback is known for its wild and wide-open
spaces, clean air, and breathtakingly clear night skies. Many venture to these
remote parts of the continent for the tranquillity the outback offers.
But for Agricultural Research Service
entomologist Greg Wheeler and his ARS and university colleagues, touring the
outback—along with expeditions to the pristine Australian
coastlines—was much more than mere adventure. Their trips Down Under were
to search for biological control agents for highly invasive Casuarina
species, commonly called “ironwood,” “horsetail
tree,” or “Australian pine.”
Not really a pine tree, this extremely problematic weed is
infiltrating U.S. coastal areas, especially in south Florida, the Virgin
Islands, Puerto Rico, and Hawaii. In Florida it’s a problem in the
Everglades National Park and surrounding areas. Known for its rapid growth,
dense coverage, and thick litter accumulation, Australian pine inhibits growth
of native plants. It is also very salt tolerant, which allows it to grow on
coastal dunes, increasing beach erosion and interfering with nesting by
endangered crocodiles and sea turtles. Australian pine was brought into the
United States in the early 1900s as an ornamental shade tree.
Entomologist Greg Wheeler examines one of the many
Australian pines in the Everglades of southeast Florida.
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But something went terribly wrong.
“While there are some fine qualities to
Casuarina,” says Wheeler, who’s in ARS’s Invasive
Plant Research Laboratory (IPRL) in Fort Lauderdale, Florida, “its
negatives far outweigh its positives.”
The Australian pine problem includes three Casuarina
species: C. equisetifolia, C. glauca, and C.
cunninghamiana.
In the past few years, the Australian members of the
teamMatthew Purcell, director of ARS’s Australian Biological
Control Laboratory (ABCL) in Indooroopilly, Queensland, ABCL researcher Bradley
Brown, and Gary Taylor from the University of Adelaide,
Australiaconducted five separate trips throughout Australia. They were
joined in a May 2007 expedition by IPRL research leader Ted Center. In all, the
expeditions covered more than 5,000 miles in northern and eastern Australia,
encompassing much of the Northern Territory and the states of Queensland, New
South Wales, and Western Australia.
Distorted branch tips of Australian pine. This
kind of damage may be caused by small, wood-boring weevil larvae.
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Purcell, Brown, Taylor, and John Gaskin, research leader of
ARS’s Pest Management Research Unit in Sidney, Montana, comprise a
Casuarina research team. Wheeler served as the lead
scientist for the project, coordinating the funding, surveys, and plant DNA
testing. (See sidebar, facing page.)
From a bounty of some 300 wasps, weevils, stem borers, sap
suckers, seed eaters, and others, the scientists have narrowed the field of
potential control agents to about 12 candidates that attack not just C.
equisetifolia, but also C. glauca and C. cunninghamiana.
One of the main thrusts behind the survey work has been to find seed, flower,
or fruit feeders to halt reproduction without destroying parent trees.
“Many Floridians enjoy the shade provided by these
trees,” says Center, “but don’t like it when
Casuarinas invade our natural areas.”
Among the top finds were the seed eater Bootanelleus
orientalis, which is host specific to Australian pine, and a defoliator
moth, Zauclophora pelodes. Many others are yet to be classified, and
some were previously unknown to science. Most of the identifications were
conducted by taxonomists at various participating institutions, with the
Commonwealth Scientific and Industrial Research Organization’s Australian
National Insect Collection in Canberra leading the way.
Pink leaf-tip galls are caused by a not-yet-identified
Cecidomyiidae midge. The galls deform branchlet growth, reducing development of
young tips. (D1206-1)
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These insects are still being tested by Purcell and colleagues
in Australia to determine their suitability for biological control here in the
United States.
“We’re pleased with the results so far and
hope for more good news once further classification is completed,” says
Wheeler.
With a keen interest in the results of the expeditions, the
South Florida Water Management District, the Florida Department of
Environmental Protection, and the National Park Service have all helped in
funding this research.By Alfredo Flores,
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.
Ted Center and
Gregory S. Wheeler are in the
USDA-ARS
Invasive
Plant Research Laboratory, 3225 College Ave., Ft. Lauderdale, FL 33314;
phone (954) 475-6543 [Center], (954) 475-6546 [Wheeler], fax (954)
476-9169.
John Gaskin
is in the USDA-ARS
Pest
Management Research Unit, 1500 N. Central Ave., Sidney MT 59270; phone
(406) 433-9444, fax (406) 433-5038.
Matthew
Purcell and Bradley Brown are
with the USDA-ARS Australian
Biological Control Laboratory, 120 Meiers Rd., Indooroopilly, Queensland,
Australia 4068; phone 011-61-732142847, fax 011-61-732142815.
Potential future adult weevil biocontrol of
Australian pine.
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Sorting Out Who's Who Among Confusing
Casuarinas
The saga of finding helpful Australian insects to stave off the
spread of unwanted, pinelike Casuarina trees in Florida comes complete
with its own mystery: It is often difficult to tell the various Casuarina
species and subspecies apart.
Hidden amidst this confusion is a particularly taxing
Casuarinaone long suspected of being a hybrid. It has no name,
and no one knows, for certain, who its parents are.
The uncertainty about who’s who among the Sunshine
State’s lookalike Casuarinas poses a problem to ARS scientists
who may someday need to match Casuarina-quelling insects from
Australiathe tree’s homelandto invader Casuarina
trees in Florida. The trick is to put the insects on the exact
Casuarina species that they evolved with in Australia. Perfect matches
may be critical to the critters’ success in stopping the uncontrolled
advance of the weedy tree.
Potential future adult weevil biocontrol of
Australian pine.
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For botanist and research leader John Gaskin at Sidney,
Montana, the Casuarina conundrum is like others he has
encounteredand resolved. He’s already tackled the tangled lineages
of tamariskanother notorious intruderand is currently making his
way though the genetic jungle of hawkweeds of the Pacific Northwest, for
example.
To solve the Casuarina puzzle, he’s using
samples of DNA of Casuarinas from Australiawhere their
identification is certain. He’s comparing that DNA to DNA from the
Casuarinas currently running amok in south Florida.
Technicians Kim Mann and Jeannie Lasseywith
Gaskin’s research unitextract DNA from pine-needle-like leaves that
Gaskin collected in 2006 from Casuarinas growing along
Australia’s eastern coast, as well as from specimens that colleagues Matt
Purcell, Gary Taylor, and Greg Wheeler gathered elsewhere in Australia and in
Florida.
Potential future adult weevil biocontrol of
Australian pine.
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The study is the first to use DNA to definitively identify the
Florida Casuarinas. Making the correct identification is “a
problem that can’t be solved by merely looking at the shape of the
trees’ leaves or conelike flowers,” says Gaskin.
He expects to have final results sometime this year.By
Marcia
Wood, Agricultural Research Service Information Staff.
"In Search ofBiological Control Agents for the
Invasive Australian Pine" was published in the
September
2008 issue of Agricultural Research magazine.
Potential future adult torymid wasp biocontrol of
Australian pine.
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