The state is moving closer to releasing insects from Asia and Africa to help combat three harmful invasive species that have taken hold in the Islands.

State officials have completed a final environmental assessment on the proposed release of a tiny African parasitic wasp to battle infestations of the erythrina gall wasp, which has destroyed native wiliwili and other trees here. Officials are waiting for federal approval and hope to release the parasitic wasp by this summer.

The state is also seeking federal approval to release — possibly by the end of this summer — a parasitic wasp found in Taiwan to control nettle caterpillar populations, as well as seeking state and federal permits to release an African moth whose larva eats toxic Madagascar fireweed.

It's believed Hawai'i would be the first in the world to deliberately release these particular insects for pest control, if approval comes through.

"We're kind of the leaders in all three of these," said Neil Reimer, head of the state agriculture department's plant pest control branch. "And we've got a lot of other countries kind of knocking on our door. When we release it they want to get it, too."

In the meantime, the U.S. Forest Service is also on track to release a Brazilian scale insect to attack strawberry guava — a serious threat to native forests — as early as this summer. That would also mark the first time this insect is ever released for biocontrol, said Tracy Johnson, research entomologist with the Forest Service's Institute of Pacific Island Forestry.

The pending insect releases follow years of searching for a natural enemy of these invasive species, testing in a containment facility and field studies in the species' native countries. Finding a predator that will specifically target a pest without harming other species is key.

For example, state exploratory entomologist Mohsen Ramadan brought back from Africa eight to 10 possible natural enemies of fireweed, but researchers found that some of them will feed on Island native plants and thus scratched them from the project, Reimer said. Ultimately, only one — the arctiid moth Secusio extensa — was determined safe for release, he said.

Scientists say the insects planned for release have been tested on numerous other species to provide evidence they would attack only the targeted pests.

That means the populations of the newly introduced insects should fall as the invasive species they feed on decline, they say.

In the case of the moth to target fireweed, there was some evidence that the caterpillar fed to some extent on sunflowers, but it was minimal, and the caterpillar preferred fireweed, Reimer said.

Draft environmental assessments on the biocontrol projects for the fireweed, nettle caterpillar and strawberry guava are available for public comment through May 23.

The release of alien species to control pests isn't a new practice for the state. More than 670 species were released for biocontrol between 1890 and 1985, according to the state Department of Agriculture. Of those, 243 became established in Hawai'i, with others dying out after being released.

But some of those early introductions would not have been approved under today's scientific and environmental standards, Reimer said.

Beginning in the 1960s and 1970s, Hawai'i entomologists began focusing on not only how effective the biocontrols are but how they could affect other species.

The state has released 43 biocontrol organisms since the early 1970s, none of which posed problems, Reimer said.

"When ... (people) hear biocontrol, they always think mongoose," Reimer said, referring to the introduction of day-hunting mongoose to kill nocturnal rats in the 1880s. "And I try to tell them, mongoose was never a biocontrol project, it was just someone who wanted to bring it in to control rats. It wasn't a science-based biocontrol project, which is what we do now."

The last time the state brought in an alien species for pest control was in 1999, when officials released a tiny parasitic wasp from Guatemala to control the citrus black fly, which was damaging crops on the Big Island and Maui, according to the agriculture department.

As the citrus black fly numbers dropped, so did the Guatemalan wasp population, and now both are at very low levels, Reimer said.

Scientists make it clear that biological control won't completely wipe out the invasive species.

"It's just going to knock the population of the pest down to lower levels so it's not a problem anymore," Reimer said.

It's unclear how long it would take for the insects to make an impact, with estimates ranging from several months to a few years.

Whether the impact will be sufficient also remains to be seen. Reimer noted the moth that would target fireweed may also be vulnerable to predators here.

The state Department of Agriculture and U.S. Forest Service conduct rigorous testing to make sure biocontrol projects are safe, said Christy Martin, a spokeswoman for the Coordinating Group on Alien Pest Species, a consortium of public and private interests dedicated to protecting Hawai'i from invasive species.

She said the group is comfortable with the release of the four insects.

"We have reviewed the testing procedures," she said. "Although we don't think any of these things are going to be silver bullets, we do think it will actually help."

The erythrina gall wasps, native to Africa, target trees like the native wiliwili and non-native tropic coral and coral trees, and have been described as one of the most environmentally damaging and costly invasive species to wind up in Hawai'i in decades. Pesticides have done little to control them, and they have no natural predators in the Islands.

State scientists hope the tiny parasitic wasp Eurytoma will effectively counter it. The female Eurytoma attacks gall wasps by inserting its egg into a gall inhabited by a wasp larva. When the egg hatches, that larva feeds on the gall wasp larva.

The state's proposed biocontrol tool against the inch-long nettle caterpillar — which has bristly stinging hairs that can cause welts, blisters and rashes in humans — is the parasitic wasp Aroplectrus dimerus. The wasp lays its eggs on the nettle caterpillar; when the larvae hatch, they feed on the caterpillar.

The larvae of the moth Secusio extensa are voracious eaters of Madagascar fireweed leaves and terminal shoots, the agriculture department said. Fireweed has infested thousands of acres of pastures and rangelands on Maui and the Big Island and is highly toxic to cattle and other grazing animals that eat it.

Strawberry guava, considered one of the most serious threats to native forests here, was introduced to Hawai'i in 1825 and spread rapidly, crowding out native species on thousands of acres of forests.

The scale insect, Tectococcus ovatus, feeds on the strawberry guava — also known as waiawi — and will hopefully stop its spread, said Johnson of the U.S. Forest Service. He said additional management measures will still be needed.

Johnson expects to initially release a few hundred of the Tectococcus, allow them to multiply in the field, and then spread them to other areas. The initial release is planned for the Ola'a Forest Reserve on the Big Island, with releases in other forest reserves and natural area reserves expected to follow.

He said he hopes to see the insects' impact at specific sites within two to three years.