PHOTO BY M. TREMBLAY / COURTESY OF HAWAII DEPARTMENT OF AGRICULTURE
The Erythrina adult female gall wasp, shown here, is 1.5 millimeters long. Adult males, not shown, are 1 millimeter long.
Wasp threatens native trees
Researchers have yet to find an effective pest-control method
Andy Graham found something last week that he'd been looking for over a year, and hoping he'd never find: signs of Erythrina gall wasp infestation in wiliwili trees on his ranch.
The native trees are just starting to put out leaves on Nu'u Mauka Ranch on the south slope of Haleakala, Graham said.
But the leaves Graham saw last week "are looking bumpy and starting to twist," he said. "It's terrible."
It's the sign of infestation by the Erythrina gall wasps, which lay eggs in tree leaves and stems. The wasp's emerging larvae then eat the young leaves.
The wasps attack only trees of the genus Erythrina, which include wiliwili trees, which are found only in Hawaii, and coral trees, species of which are used as ornamental trees and as windbreaks on the edge of fields, said Lloyd Loope, a botanist for the U.S. Geological Survey on Maui.
The minuscule wasps (1 to 1.5 millimeters in length) originated in Africa, but are believed to have come into Hawaii via Taiwan.
The first sign of the wasps was on Oahu in April 2005, Loope said. By July 2005, they were spotted on Maui and now are believed to be on all the major islands.
So far, no attempts to stop the rapid invasion or stop the wasps' effects on Erythrina trees have been successful, Loope said.
The main hope for saving Hawaii's wiliwili and coral trees is research being done now on a predator wasp, also from Africa.
But extensive testing by the state Agriculture Department must prove that the predator wasp will only eat the Erythrina wasp and not other beneficial Hawaii insects, said Steve Montgomery, an entomologist and conservation biology consultant.
Montgomery said he hopes the state or federal government will spend $10 million to build more biologically secure facilities in which such tests can be done.
The quickest such testing, which began in November, can be completed would be in three years, Loope said.
Graham said he hopes his trees can last that long.
The wiliwili tree, which flowers in colors ranging from white to pink to orange, sheds its leaves in the hot summer months and sprouts new ones in the fall.
In addition to being "keystone" species in lower-elevation dry forests, the wiliwili is culturally important to native Hawaiians, who used its wood for canoes and surfboards, said Art Medeiros, coordinator of the Leeward Haleakala Watershed Restoration Partnership, which includes all landowners on Haleakala's Leeward side.
Montgomery said he'd classify the gall wasp problem in the "top five" of invasive species problems in Hawaii, because the wiliwili tree "is a native species, so prominent in lowlands on all islands."
"I first saw the gall wasp on Oahu in July of 2005 and when I saw it my heart just dropped," Loope said. Ironically, the damaged coral trees he saw were right in front of the state Department of Agriculture's Plant Quarantine Station.