Crews are cutting down more than 1,000 trees in city parks and medians that are suffering from infestations of a tiny African gall wasp that threatens to cost the city and state millions of dollars in tree removal and replacement.

Just over a year after first being detected in Manoa, the wasp has spread statewide, leaving scientists scrambling to find a natural predator or a formidable pesticide.

In Honolulu, the wasps have killed hundreds of large shade trees in parks, along streets and in walking squares, and threaten to sharply deplete the inventory of greenery in the urban core.

When the trees die, officials say, they grow brittle and pose a danger.

Work started two weeks ago to remove dead trees on city park grounds or in medians, and already about 400 have been chopped down, said city Division of Urban Forestry Chief Stan Oka. A $440,000 contract was awarded to handle the job, which includes cutting down the trees and shaving down their trunks.

This is the latest in a spate of tree removals brought on by the wasp's destruction. In August, a cluster of trees was pulled out of Magic Island and dead trees have also been pulled out of Ala Moana Beach Park, Ke'ehi Lagoon Park and other spots. Other city trees under different departments are not included in the latest contract.

Meanwhile, hundreds more trees on state lands are also destined for removal, though officials have no full accounting of the problem. Several state agencies, including the Department of Land and Natural Resources, are undergoing reviews to find out how many of their trees are infested.

"It's wiping out all these urban trees," said Paul Conry, administrator for the state forestry and wildlife division. "It's creating a real source of liability. There's going to be lots of trees dying."

The gall wasps, which are not harmful to humans, infect trees in the genus Erythrina that includes the indigenous wiliwili and non-native tropic coral and coral trees. Scientists fear the insect could push the wiliwili into extinction. The tree is found only in Hawai'i.

Coral trees are one of the most common landscape trees in Ho-nolulu and elsewhere, and the tall, spindly tropic coral tree is often used as a windbreak around farms statewide.

"It's a huge problem. The trees are dying everywhere," said Bob Loy of the Outdoor Circle, which is working with the city to identify infested trees. "The loss of these trees is a tragedy that will probably take generations for Hawai'i to recover from."

The state and city are working on re-planting plans, but money for those projects could be slow in coming. Oka said replacing the uprooted trees will "cost a lot of money," though he had no immediate figures. The replacement trees will likely be large, but not fully grown.

"It's a long, tough process, but we plan to do something," Oka said.

Affected trees on school grounds are also a cause for concern. Gary Yasui, who coordinates school inspections for the state Education Department, said crews are trying to identify infested trees. During a recent routine tree trimming at schools statewide, he said, several problem trees were noted.

So far, state and University of Hawai'i scientists trying to save the trees have had underwhelming results with pesticides and are still far off from approving a biological control for release.

In March, the state Department of Agriculture announced a natural predator to the gall wasp had been found after a trip to eastern Africa. The insect feeds on gall wasp larvae and pupae.

But Janelle Saneishi, spokeswoman for the Department of Agriculture, said tests to determine whether the predator could be released in large numbers in Hawai'i will take at least a year.

State forest health coordinator Robert Hauff, of DLNR, said some insecticides have slowed the degeneration from the wasps. A few trees have even sprung back to health.

On Wednesday, contractor Geoff Eldridge was applying insecticide to infested trees outside the state Department of Land and Natural Resources building for free to see whether his application worked.

Eldridge drilled holes into trees, then injected insecticide with a high pressure gun.

Nathan E. Dodds, president of J.J. Mauget, the California-based firm providing the insecticide for the test, said the method has shown promise in combating a smaller gall wasp problem on Guam. The insecticide Dodds uses disperses to the leaves and prevents the wasps from eating.

Reach Mary Vorsino at mvorsino@honoluluadvertiser.com.