UF study: Cloning insect-fungus duo kills 500 million trees

Dan Florida, Forestry, Research

by Ellison Langford, University of Florida Institute of Food and Agricultural Sciences

treesLaurel wilt disease has killed as many as half-a-billion trees. And,a new study by a researcher with the University of Florida Institute of Food and Agricultural Sciences suggests it may have been spread by a single insect cloning itself.

“In biology, there is no evidence of a single strain pathogen killing so many hosts in such a short period of time,” said Jason Smith,  an associate professor in the UF/IFAS School of Forest Resources and Conservation..

According to Smith, the purpose of the study was to determine the genetic diversity of the pathogen and its beetle vector, and to provide an estimate of how many trees laurel wilt has claimed.

redbay ambrosia beetle (xyleborus glabratus)
Courtesy: University of Florida/IFAS

Laurel wilt is caused by a fungal organism that latches onto the redbay ambrosia beetle. Native to Southeast Asia, the beetle transmits the disease to trees in the Lauraceae family and uses wilted trees as sites for reproduction. Members include sassafras and avocado, but the chief victim has been the redbay.

Research indicates that laurel wilt has killed about 320 million redbay trees since its introduction in 2002 in Eastern Georgia– or 30 percent of the species’ population. The disease has spread throughout Florida, up to North Carolina and west into Texas.

“We think it could potentially get to Mexico and Central America where the Lauraceae is a dominant plant species,” Smith said.

The Laurel wilt disease is spread by the redbay ambrosia beetle, and once an avocado tree is infected, it may die in as little as 6-8 weeks.
(Photo by Paul Kendra.)

Florida has an annual $100 million avocado industry, and Central America is a world leader in avocado production, he said.

The disease is transmitted when the beetle bores into the tree and deposits spores into the tree’s vascular system. As the spores are carried along, the tree’s defense system reacts, and shuts down the vascular system.

“Trees are dying as a result of overreaction to the fungus, rather than the fungus actually doing anything to kill the trees,” Smith said.

The disease has a 95 percent mortality rate. In hot weather, trees can die within weeks. The death of so many trees has wreaked havoc on local ecosystems.

“Redbay is a very important plant for many organisms, including bears, lots of birds, butterflies,” Smith said. “[Certain] butterflies depend of members of the Lauraceae for food during their larval development.”

Also, the disease has devastated swamp bay populations in the Everglades.

“That’s what’s really so amazing about it this,” Smith said. “A beetle no larger than Lincoln’s nose on penny could have led to the death of half-a-billion trees and counting and all of the radiating effects at the multiple trophic levels.”

Researchers suggest the insect’s unusual capabilities may be the key to redbay restoration.

The odds of not only the insect being clonal, but also the pathogen it carries, are astronomical, Smith said. “However, this means that the red bay beetle will be hard-pressed to make the adaptations necessary to continue infecting disease-resistant redbays as they are re-introduced,” he said.

The study is published in the journal Biological Invasions. Click here to read the study.

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