HONOLULU — The wiliwili trees began dying in the summer of 2005. Since then, wiliwili groves on all the Hawaiian islands have been devastated, leaving barren plains in their stead.
For each tree, it was the same process: First, gnarled lumps would appear on the leaves. Then the leaves and branches would turn brown. Within months, the tree would be dead.
Scientists determined that the culprit was a tiny predatory wasp from Africa, only recently discovered by science. Botanists named it the erythrina gall wasp: erythrina for the type of tree it attacks, and gall for the tumors it creates in leaves. An adult gall wasp is one-third the size of a typical mosquito.
"It's tiny, like dust, but the damage it causes is unbelievable," said Mohsen Ramadan, a state entomologist who characterized the epidemic as one of the worst problems ever caused in Hawaii by an invasive species. Trees killed by the gall wasp number in the thousands, from inner-city neighborhoods in Honolulu to rural farms on Molokai and desert-like plateaus on Kauai and the Big Island -- all in a short period.
Now, state officials hope to introduce a predator from Tanzania, the eurytoma wasp, as the last best hope to save the wiliwili trees. Officials must first prove the new insect will not harm any other species. The approval process, according to Ramadan's boss, Neil Reimer of the state Department of Agriculture, could take three months or three years. The state is also seeking comments from the public.
Introducing new species as a biological-control agent has always been a tricky proposition in Hawaii, where nonnative plants and animals have wreaked havoc on native species. The best known biological-control failure involved the mongoose.
The sugar industry brought them to Hawaii to control the rat population (believed to have been brought by ancient Polynesians). But the mongooses, active chiefly in the daytime, did not prey on nocturnal rats. Instead, they went after the islands' native birds. Mongooses continue to menace bird populations on the islands.
"We're going to win some, we're going to lose some," said Art Medeiros, a biologist on Maui. Medeiros is collecting and preserving the seeds of native wiliwilis in case the trees are wiped out by the gall wasps. He said if native wiliwilis died off, vast stretches of land on Maui would become deserts.
