AgCenter joins study of tree decline in Guam

(12/02/20) BATON ROUGE, La. — A researcher in the LSU AgCenter Department of Entomology has joined a scientific team investigating the role of termites in killing an important tree in the U.S. territory Guam.

Claudia Husseneder’s role will be to study the termites infesting ironwood trees and identify the microorganisms in the termite gut and their role in spreading tree disease.

The study is funded by U.S. Department of Agriculture grants totaling almost $370,000.

More than 18 years ago, the ironwood tree — a hearty, salt-resistant species important for soil erosion control and a protector of vegetation from the wind — unexpectedly began dying in Guam. This condition is now referred to as ironwood tree decline. Six years later, researchers identified the main culprit as the bacterial wilt pathogen known as Ralstonia solanacearum.

A survey in 2008 estimated that 51% of the trees were showing signs of ironwood tree decline. Numerous sick or dead trees were under termite attack, but the species of termites were not identified.

“We know the termites chew on the roots, so it’s very possible that the termites are carrying bacteria either internally or on the outside of their body,” said principal investigator Robert L. Schlub, a researcher in the University of Guam Cooperative Extension and Outreach unit. “Because of this correlation between the termites and disease, we think they are likely the means of transmitting it.”

In a recent study, Husseneder confirmed that the termite species most frequently found to have a taste for ironwood trees was Nasutitermes takasagoensis.

Husseneder and an LSU graduate student will identify the bacteria associated with the termites attacking ironwood trees to determine if they’re carriers of the plant pathogens.

“Because termites are significantly associated with ironwood tree decline, we will investigate whether they carry bacteria causing ironwood tree decline in their guts as a first step to explain their potential role as vectors,” she said.

Researchers in Guam will collect termites from both healthy trees and diseased trees and send them to Husseneder to compare termite gut bacteria from trees with different degrees of infection and those with and without confirmed Ralstonia or other pathogen infections.

Over the course of the project, the researchers will conduct educational workshops to teach how to distinguish between the termite frequently attacking Guam ironwood trees and another termite commonly known as the Philippine milk termite, which is endemic to that part of the world and is a serious threat to wooden structures.

The workshops also will help the public, farmers and foresters learn about tree care practices such as disinfecting pruning tools to reduce the spread of bacteria.

Scientifically known as Casuarina equisetifolia, ironwood trees are ecologically and economically important trees in tropical and subtropical regions of the Indian and Pacific oceans. Their lifespan is 35 to 90 years, and they can grow to nearly 80 feet tall and 3 feet in diameter.

Ironwood is recognized as an important tree species by the U.S. Department of Agriculture Natural Resources Conservation Service. Its value is underscored by the fact that it has been on Guam for thousands of years and is tightly integrated into the island’s environment.


Nasutitermes takasagoensis is the termite species most frequently found to have a taste for ironwood trees.

12/2/2020 7:44:43 PM
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