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The Honolulu Advertiser
Posted on: Sunday, August 7, 2005

Tiny wasp may kill off native trees

By Timothy Hurley
Advertiser Staff Writer

The rapid spread of Erythrina gall wasps in the Islands is alarming many local conservationists.

Hawai'i Department of Agriculture


A tiny new species of wasp has invaded Hawai'i and is rapidly spreading across the Islands, threatening to kill off a popular family of trees that includes the native wiliwili, a species mentioned in the ancient creation chant the Kumulipo, and used in Hawaiian tradition to craft surfboards, canoe outriggers and fish net floats.

Since its discovery in April, the Erythrina gall wasp has spread on O'ahu, leaving an unsightly trail of defoliation among erythrina species such as the red-flowering Indian coral tree and the tall wiliwili, a fast-growing non-native commonly used as a windbreak and as a highway noise and privacy buffer.

And in just the past few weeks, the wasp has been discovered damaging trees on Kaua'i, Maui and the Kona side of the Big Island.

"It's so prolific and rapidly dispersing that we just can't stop it," said Ken Teramoto, chief of the biological control section of the state Department of Agriculture.

The problem is so bad that some members of the conservation and science community are busily preparing for the worst — collecting seeds from the native wiliwili, E. sandwicensis, just in case the population of the ancient low dryland forest tree is wiped out.

The invasion is bad news not only for those trying to safeguard native species, but also for the agricultural industry, taxpayers and the public at large. The Indian coral tree, or Erythrina variegata, is a popular plant in public gardens and parks. And the fast-growing tropic coral, known locally as tall erythrina or tall wiliwili, is widely used on agricultural lands as a windbreak for soil and water conservation and by private homeowners to block traffic noise and prying eyes.

Replacing or treating the sick and dying trees isn't going to be cheap, predicted Randy Bartlett, vice chairman of Hawai'i's Coordinating Group on Alien Pest Species.

"It's pretty dramatic the damage this is causing," said Bartlett, who manages the Pu'u Kukui Watershed for Maui Land & Pineapple Co.

The problem is so new that officials aren't sure what to do. The Erythrina gall wasp was first identified only last year by a Korean scientist who examined specimens taken from Singapore, Mauritius and Reunion islands.

Since that time, Taiwan has reported struggling with coral tree damage caused by the same wasp, and officials here suspect the tiny insect — the male is 1 millimeter in length, the size of a grain of sand — made its way to Hawai'i in a shipment from Taiwan.

In Hawai'i, samples of wasp-damaged coral tree leaves were first collected in Manoa by a University of Hawai'i graduate student in April. A state Department of Agriculture survey at the time found it only in certain leeward areas of O'ahu and Honolulu.

The leaf damage, or gall, is a reaction to wasp larvae developing within the plant tissue. According to scientists, trees with heavily galled leaves and stems lose their vigor, become defoliated and can die.

The damage is not pretty. Lloyd Loope, research scientist with the U.S. Biological Resources Division's Haleakala Field Station, traveled to O'ahu last week and observed lots of "incredibly ugly" erythrina trees hanging on for life.

"It's even worse than I dreamed," Loope said.

Honolulu's city-run botanical gardens have been hit hard. The five gardens are home to a diverse collection of erythrina trees, accumulated with the help of botanical gardens from around the world. But now many of those trees are being crippled.

"There are no deaths yet, but it looks like it's coming," said Joshlyn Sand, Honolulu Botanical Gardens horticulturist.

Sand said erythrina seeds and cuttings are being collected for preservation in a nursery.

On Maui, there's a growing fear that the state's largest intact stands of native wiliwili will be destroyed. Loope's USGS colleague, Art Medeiros, has dedicated a great deal of time to preserving native forest on the leeward side, where the wiliwili is the keystone species of the low dryland forest. But all of his work — and that of the many volunteers who worked on projects such as the 236-acre Pu'u O Kali preserve — could be lost.

Medeiros estimated that 10,000 to 20,000 wiliwili grow on southern Haleakala, a population now in the midst of one of the most spectacular flowering years in memory.

"If this is the last great flowering of the wiliwili, it's a sad day for Hawai'i," he said.

Officials say the only immediate hope is that the gall wasp brought with it a companion parasite that might, given time, help keep the gall wasps in check. A similar thing happened last year when a parasitic wasp emerged to help combat a white fly infestation.

But there isn't much optimism for a repeat of this phenomenon, Loope said, since no such parasite has emerged in Taiwan and this species has been spreading with lightning speed.

There has been talk about an all-out eradication effort on Maui. Medeiros has been talking with experts, conducting surveys and trying to arrange a meeting with Maui Mayor Alan Arakawa. He said a strategy of clipping leaves, mulching and tarping might beat back the onslaught.

But the state Department of Agriculture's Teramoto, an entomologist, said he believes the effort would be a waste of time and resources.

"It's impossible to stop. It's going to do its dirty deed," he said.

The only true form of eradication, he added, would be to destroy all erythrina trees, including the natives, but he doubts there would be much support for that.

"The best thing we can do is just ride it out and hope another (companion) case of biocontrol emerges," Teramoto said. If not, a natural enemy of the wasp may have to be imported to Hawai'i from Africa, where this kind of wasp is endemic, he said. But that will take time.

In the meantime, a seed weevil has also targeted these trees, Bartlett noted, and together they may act as a double whammy to seal the tree's fate.

"It could push the wiliwili over the edge of extinction," Bartlett said. "That's a pretty terrifying thought."