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Leaf-Weevil Proves Successful Against MelaleucaBy Jesús García
April 28, 2000
After being released two years ago by Agricultural Research Service scientists, the leaf-weevil Oxyops vitiosa is proving highly effective at defoliating existing stands of melaleuca saplings and will likely prevent further spread of this invasive tree.
Melaleuca quinquenervia, or broad-leaved paperbark tree, naturally inhabits areas along the east coast of Australia from the northern tip of Queensland and parts of Papua New Guinea down to Sydney in New South Wales. In these areas, the tree is held in check as part of a balanced environment.
This fast-growing tree was imported into Florida in the late 19th century. Later, it was planted as a way to drain the Everglades and now infests nearly 500,000 acres of wetlands. The tree is widely considered to be transforming the Everglades from a wet prairie to a closed-canopy swamp forest. Estimates of annual losses range as high as $168 million.
Researchers with ARS Aquatic Plant Research Unit in Ft. Lauderdale, Fla., led by entomologist Ted Center, have sought alternatives to the traditional forms of melaleuca control: felling of mature trees, removal of saplings by hand, burning, and herbicides. Infestation is likely to recur after use of these techniques unless follow-up eradication measures are employed. Biological control is being used to complement these methods.
After extensive testing of the 6- to 9-millimeter-long native Australian leaf-weevil and its larvae--for more than a decade by ARS scientists in Australia and Florida--more than 1,550 adult weevils and 6,700 larvae were released at 13 sites in six counties between the spring of 1997 and June 1998. ARS researchers have recently found that those populations are now well established, increasing and beginning to disperse to other infested areas.
Every year each melaleuca tree naturally loses 25 to 33 percent of its leaves. But the leaf-weevil is so proficient at consuming any new leaves that over time some trees could become completely defoliated. Some are already exhibiting tip die-back. Ultimately, the weevil will alleviate one of the biggest problems associated with controlling melaleuca--its ability to disperse millions of seeds when it dies.