Aussie Weevil Opens Attack on Rampant
Visitors attending the first release of melaleuca leaf weevils near Fort
Lauderdale, Florida, walk on a trail made of melaleuca chips surrounded by
50-foot-high melaleuca trees
Hardworking insects imported from Australia to attack melaleuca trees may
help stop this weed from overrunning Florida's Everglades.
Native to Australia, melaleuca has successfully invaded more than a
half-million acres in central and southern Florida since the early 1900s. The
trees take over an estimated average of 14 to 15 acres a day, threatening to
destroy the delicate Everglades ecosystem.
Agricultural Research Service
scientists and cooperators freed the grey-brown melaleuca leaf weevil,
Oxyops vitiosa, for the first time in the United States this year,
turning loose about 1,600 of the short-snouted insects at 11 key
melaleuca-infested sites in Florida. Their work marks the first time that any
melaleuca-munching organism has ever been used in this country for classical
biological control; that is, the use of one introduced organism to control
The weevil's U.S. debut resulted from more than a decade of scrutiny by ARS
scientists based in Australia and Florida. Their outdoor investigations in
Australiaand laboratory and greenhouse tests both there and in
Floridashowed that the quarter-inch-long weevil would not eat desirable
plants on farms or in gardens, nurseries, and parks. Those experiments included
not only testing on melaleuca relatives like bottlebrush and eucalyptus, but
also on fruit and nut trees, shrubs, and many native plants.
An adult melaleuca psyllid female rests on a melaleuca leaf inside a Florida
Weevil adults and grubs, or larvae, feed voraciously on melaleuca's young,
silvery leaves. This stunts the plant's growth and leaf production, says
entomologist Ted D. Center, who is in the ARS Aquatic Weed Control Research
Unit at Fort Lauderdale. He directs Florida studies that now include careful
monitoring of the weevil's success in colonizing the state's melaleuca groves.
More of a Good Thing
Scientists want to augment the weevils with other industrious insects. The
most promising candidates include four additional species native to Australia:
a beneficial sawfly, a sap-feeding psyllid (SILL-id), a tube-dwelling moth, and
a gall-forming fly. ARS scientists are the first to extensively study the
potential of this quartet of little-known insects to thwart melaleucaand
Thin layers of peeling bark give melaleuca its nickname-- paperbark
These rigorous tests garnered the first-ever federal and state approvals to
ship the sawfly and psyllid to Florida for indoor study at the Gainesville lab.
It's a high-security quarantine site, meaning that test insects can't sneak
outdoors. Entomologist Gary R. Buckingham of the ARS Aquatic Weed Control
Research Unit heads the Gainesville studies.
Portrait of the Enemy
Known to botanists as Melaleuca quinquenervia, this invasive pest is
native to Australia and a few neighboring islands. Layers of paper-thin bark
give the weed its "paperbark tree" nickname. Thirsty and
fast-growing, melaleuca was brought to this country in 1906 and widely planted,
in an attempt to dry up Florida marshes and swamps. It is not a pest in
A mature melaleuca tree produces millions of brownish-black seeds every
year, each about the size of a pepper grain. Even if only a few of these seeds
sprout, vigorous melaleuca saplings can quickly crowd out native plants, says
entomologist Joseph K. Balciunas. Now at the ARS Western Regional Research
Center in Albany, California, Balciunas is former director of the ARS
Biological Control Laboratory at Townsville, Australia.
In a quarantine facility, colonies of melaleuca psyllid nymphs feed on
melaleuca saplings, sometimes killing them.
While there, he led pioneering investigations that revealed biological
control candidates. Balciunas did this work for ARS from 1989 to 1995 with
co-researchers Matthew F. Purcell and Peter K. Jones of Australia's CSIRO, or
Commonwealth Scientific and Industrial Research Organization, in Brisbane; and
Damien W. Burrows of the Australian Center for Tropical Freshwater Research,
James Cook University, Townsville, Australia.
The ARS labnow headquartered in Brisbane and previously in Townsville
at James Cook Universityis jointly operated by ARS and CSIRO. Balciunas
was succeeded as lab director in 1996 by Charles W. Turner, an ARS research
botanist who died in 1997.
The Agents' Modus Operandi
At the ARS Aquatic Weed Control Research Unit in Gainesville, Florida,
Australian researcher Matthew Purcell (left and ARS entomologist Gary
Buckingham examine growth of young melaleuca plants.
Biological control researchers agree that the insect most likely to follow
the melaleuca leaf weevil may be the sawfly Lophyrotoma zonalis. Larvae
of this aggressive herbivorous insect have a hearty appetite for tough old
Each inch-and-a-quarter-long sawfly larva "has a tiny horn on its back,
making it look something like a little hornworm caterpillar," says
Buckingham. His greenhouse tests demonstrated that a troop of 100 sawfly larvae
can destroy every leaf on a 10-foot-high melaleuca sapling in only 3 or 4 days.
Melaleuca's clear sap makes a nutritious meal for a sap-sucking insect known
as Boreioglycaspis melaleucae, or melaleuca psyllid. Psyllids are also
called jumping plant lice because the highly active adults, which resemble
miniature cicadas, jump between leaves and plants when alarmed.
Melaleuca leaf weevils, Oxyops vitiosa, were released this year in the
Florida Everglades as a biological control of melaleuca trees.
Both the adults and young, or nymphs, feed on melaleuca sap. Nymphs cause
the most harm, severely damaging seedlings. In tests conducted by Balciunas,
Purcell, and Jones, it took about 500 nymphs only a week or two to cause leaves
of potted melaleuca saplings to begin curling and withering. After about a
month of this onslaught, some besieged saplings died.
Psyllid nymphs, says Balciunas, typically form a communal shelter of
delicate white threads. These house dozens of nymphs, making it easy for
scientists to find and collect the insects for lab tests there or in Florida.
The leaf-eating larvae of a tube-dwelling moth called Poliopaschia
lithochlora "do a competent job of attacking and destroying melaleuca
saplings," says Burrows.
To defend themselves, larvae live in colonies, building an elaborate system
of sturdy, quarter-inch tubes. They loosely drape the tubes with a
whitish-brown webbing. Strong and somewhat like spun silk, the webbing anchors
the colony to melaleuca branches. The busy larvae venture from the tubes to
gather melaleuca leaves, which they attach to the webbing. A typical network of
tubes and webbing may be up to 6 inches long and 4 inches across and may
accommodate at least a half-dozen larvae.
A melaleuca sawfly adult prepares to deposit eggs on a melaleuca
A swelling called a gall makes a cozy home for another kind of melaleuca
herbivore. Immature gall-forming flies, members of the genus Fergusonina,
share space inside the gall with wriggly microscopic worms called
nematodes. The organisms may work together to form the typically conical galls
on the tips of melaleuca branches.
"Fully developed galls are usually about the size of a marble,"
says researcher Purcell at Brisbane. "Galls disrupt flower and seed
production because they form where the tree would normally produce new
flowers." Adult gall flies resemble very small house flies. The
nematodesa species the researchers haven't yet identifiedare
C-shaped and transparent or nearly white.
Studies elsewhere with another Fergusonina gall-forming fly showed
that nematodes invade the ovaries of the female fly larvae and are later
expelled when the female lays her eggs. "That same process," says
Purcell, "probably occurs with the fly that inhabits melaleuca galls.
"We're trying to determine if the nematode causes galls or,
alternatively, whether galls form in response to some chemical released by the
female fly when she lays her eggs. Once we find the answer, we'll know if we
need to recruit both organisms, or just one."
Melaleuca psyllid nymphs are partially covered by waxy filaments that they form
as protection against predatory insects.
Federal and state agencies cooperating in the research include the U.S.
Army Corps of Engineers, National Park Service, Florida Department of
Environmental Protection, Florida Department of Agriculture and Consumer
Services, South Florida Water Management District, and Dade and Lee Counties.
By Marcia Wood
Balciunas is in the USDA-ARS Exotic and Invasive Weeds Research Unit, 800
Buchanan St., Albany, CA 94710; phone (510) 559-5975
D. Center is in the USDA-ARS Invasive Plant Research Laboratory, 3205 SW
College Ave., Fort Lauderdale, FL 33314; phone (954) 475-6543