HAWAII DEPARTMENT OF AGRICULTURE State officials hope this biological control agent, a wasp from Taiwan, will help control the nettle caterpillar population in Hawaii.

Wiliwili pest will face wee assassin

State wants to sic tiny wasps on big pests

A pest that has already cost the city $600,000 could meet its match this summer in the form of a killer cousin.

Pending permit approvals, the state plans to release tiny wasps from Africa to act as flying assassins against the erythrina gall wasp, which has devastated Hawaii's wiliwili trees.

A second wasp will be released to attack another pest, the nettle caterpillar, under the plan.

Neil Reimer, plant pest control branch manager at the state Department of Agriculture, said biological control agents are an affordable way to keep unwanted populations down with little maintenance. Before releasing the agents, the department conducts stringent tests to ensure they do not harm other species in the wild or become a nuisance themselves, he said.

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HAWAII DEPARTMENT OF AGRICULTURE, COURTESY PHOTO State officials have imported the species of wasp on the left as a possible biological control agent for the gall wasp, shown at right. HAWAII DEPARTMENT OF AGRICULTURE State officials have imported the wasp on the left as a possible biological control agent for the nettle caterpillar, shown at right.

This summer, two notorious bugs could meet their match.

That is when state officials hope to release two tiny species of wasp that could keep the erythrina gall wasp and nettle caterpillar under control.

First, state officials must get approvals from the state and federal level to release the wasps. In a meeting later this month, the state will seek a permit from the state Board of Agriculture to release the agents this summer.

State officials blame the erythrina gall wasp for killing thousands of native wiliwili trees, a species that Hawaiians used for surfboards, canoes, medicine and leis. The wiliwili, which was mentioned in the Hawaiian creation chant "Kumulipo," has both native and non-native varieties here, all part of the erythrina genus.

As for the nettle caterpillar, its painful sting and voracious appetite have caused problems for commercial growers of palms, ti leaves, lilies and other crops, officials said.

To control the gall wasp, state officials have brought in a relative of the wasp that lays its eggs on the wasp. For the nettle caterpillar, officials have a wasp that paralyzes the caterpillar and feeds on it.

Neil Reimer, plant pest control branch manager at the state Department of Agriculture, said biological control agents are an affordable way to keep unwanted populations down with little maintenance.

Before releasing the agents, the department conducts stringent tests to ensure they do not harm other species in the wild or become a nuisance themselves, he said.

The most famous case of biological controls going haywire in Hawaii involved the introduction of mongooses in the 1880s to control rats. The move backfired because rats are nocturnal and mongooses diurnal -- or day creatures -- and their paths did not cross.

Since its first discovery in Hawaii in 2005, the gall wasp has destroyed some 10,000 erythrina trees across the state, according to Rob Hauff, forest health coordinator at the Department of Land and Natural Resources.

"It was so suddenly explosive, it just blew up with amazing speed," he said.

Gall wasps lay their eggs in the leaves of erythrina trees, forming abnormal growths called galls. The larvae and pupae feed on and eventually kill the leaf and eventually the tree.

City crews had to remove about 1,000 non-native wiliwili trees damaged by the gall wasp, costing about $600,000, according to Les Chang, director of Honolulu's Department of Parks and Recreation.

The cost of replacing those trees could reach into the millions, he said.

Meanwhile, the native wiliwili tree has coped better because it drops its leaves in the summer, but it remains threatened by the wasp.

"We're keeping our fingers crossed," Hauff said. "Without biological control, they (native wiliwili) are pretty much doomed."

State officials found the gall wasp's natural predator in Africa. It is still unnamed.

The caterpillar's natural enemy, Aroplectrus dimerus, was found in Taiwan, where it keeps the caterpillar's presence to a barely noticeable level.

If approved, thousands of the biocontrol agents could be released around the island, Reimer said.

It could take six months to several years before the effects of the biocontrol agents become visible, he said.