An alien invader that threatens Hawaii’s iconic coconut palms appears to be spreading on Oahu and may have established a breeding population, state officials say.

Coconut rhinoceros beetles, popular as pets with the Japanese, appear to have moved west on Oahu within the past six weeks, prompting the state to expand the buffer zone from the original infestation site to a 50-square-mile area.

An eradication crew found a male coconut rhinoceros beetle May 21 in a trap in an industrial area of Barbers Point, the farthest west any of his fellow beetles have been found from the original detection site at the golf course on Joint Base Pearl Harbor-Hickam.

"I think this is more related to the expansion from the existing infestation," state Department of Agriculture acting Plant Quarantine manager Darcy Oishi said Wednesday.

"In the context of having other detections in the Ewa Plains area" and because it was "the first time we’ve had detection not associated with a high winds period, we may have a breeding population," he said.

A new breeding site was also found May 21 near a green waste storage site at Pearl Harbor-Hickam.

The beetles, first discovered on Oahu Dec. 23, are a major pest of palms in the Philippines, Fiji and Samoa, on Guam, and elsewhere.

The insects have also been trapped at Iroquois Point, Keehi Lagoon Park, Sand Island and Red Hill.

The Agriculture Department and its state and federal partners have found about 360 adult beetles, 520 larvae and 16 pupae within the original 2-mile buffer zone from the original detection zone. Crews have set 1,200 traps, and surveyed 66,000 palm trees and 150 mulch sites across the island.

No area nurseries are known to be infested.

The big black beetles have been found by the U.S. Department of Agriculture in checked bags associated with Japanese visitors, who bring them in as pets, Oishi said. He said they could have accidentally been brought in.

The nocturnal 11⁄4- to 11⁄2-inch-long beetles can fly up to 2 miles a day, but likely go unseen because they fly at night. The public can report coconut rhinoceros beetles by calling 643-7378.