Albizia is the scourge of Hawaii’s forests and a threat to power lines and roofs across the islands. With no natural enemies here, it is larger and more robust here than in anywhere else on Earth, including its native range.
That may be about to change. Kenneth Puliafico and Tracy Johnson, researchers with the U.S. Department of Agriculture’s Institute of Pacific Islands Forestry, have been searching for biocontrol agents. As Puliafico recently reported at a science conference in Hilo, they identified the source of the albizia introduced in Hawaii in 1917, tracing it back to Java and Northern Borneo.
As it turns out, those islands are way outside the species’ native range.
Albizia trees have spread throughout the islands for decades.
Courtesy: Forest and Kim Starr
“What happened is, Joseph Rock must’ve gone to Borneo and Java in 1917 and brought back seeds and plant samples from there,” Puliafico said in a phone interview. (Rock, a self-taught botanist, was charged by the territorial government of Hawaii with locating species of trees that could reforest denuded slopes and restore watershed functions.)
Albizia (Falcataria moluccana) has been grown in plantations on the Indonesian islands for the last 150 years or so, with the wood being used for light construction – “disposable boxes, pallets, everything from matches, chopsticks, and shoes,” Puliafico said.
At present, he added, it’s “used for plywood and a little bit of paper pulp.”
“The native range of our albizia is much further to the east, the other side of the famous Wallace Line. It’s more associated with New Guinea island and some of the smaller islands off there,” he said.
Although it’s still a major commercial tree in the western Indonesian islands, “in its native range, it’s nearly impossible to grow commercially because of natural predators. They can put in plantations, but after 10 years, the trees are just hammered by everything.”
In 2015 and 2016, Puliafico traveled to Indonesia and Papua New Guinea on the hunt for organisms that could halt albizia in its tracks. He was able to identify several candidate species, including a rust fungus that, Puliafico said, “turns albizia into pretzels.”
“This is a disease, in the genus Uromycladium, that has been used by biocontrol practitioners in South Africa,” he said. “They used a related species to control invasive acacia plants from Australia. Extensive testing has gone into that previously. We’re looking at a related species that’s supposed to be specific to our albizia.”
“Once it got into plantation areas, it destroyed the crop of albizia,” he said.
His colleagues in Indonesia have begun testing the fungus for host specificity to see if the rust could affect the two Hawaii species most closely related to albizia – koa and koaia.
Other biocontrol candidates include a shoot-tip mining moth, which attacks young trees and slows their growth; a stem-mining weevil that feeds on the woody stems of older trees; leaf-feeding beetles; and a gall-forming mite that causes leaflets to curl up and no longer be able to photosynthesize.
Gall rust fungus on the stem of a young albizia tree.
Courtesy: Kenneth P. Puliafico
Future steps include identifying the potential biocontrol agents and ranking them by the degree of specialization, exploring their life history in their native range, and, finally, testing them for host specificity — how likely, or unlikely, are they to attack non-target species in Hawaii.
How soon might an albizia biocontrol agent be released in Hawaii? Puliafico was asked.
“If everything continues to go as well as it has now, we’re looking at a three-year window” for the first biocontrol agent to be completely tested, he replied, with additional time before obtaining all official permissions needed to release it into the environment. “Of course, if the five species we choose turn out not to have host specificity or we lose funding, that could postpone things.”
Reprinted with permission from the current issue of Environment Hawaii, a nonprofit news publication founded in 1990. All issues published in the last five years are available free to Environment Hawaii subscribers at www.environment-hawaii.org. Non-subscribers must pay $10 for a two-day pass. All issues older than that are free to the public.
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