State officials say many trees in mature koa forests of East Hawaii are losing their leaves due to a sudden, sharp increase in a native moth population.

Koa trees in nearly 25,000 acres of forest between 2,000 and 4,000 feet above sea level in the Hilo and Hama­kua regions appear to be affected.

The Department of Land and Natural Resources said Thursday that caterpillars of the koa looper moth are eating the leaves. But department Director William Aila Jr. said past experience shows koa forests can recover from such outbreaks.

"The department has determined that this defoliation event is the direct result of feeding by moth native to Hawaii, the koa looper," Aila said in a news release. "Fortunately, past occurrences of these outbreaks show us that koa forests can recover. We are thankful that researchers from the University of Hawaii, U.S. Forest Service, U.S. Geological Survey, and Hawaii Agricultural Research Center are assisting DLNR to monitor this rare natural phenomenon."

The koa looper (Scoto- rythra paludicola) is a native moth commonly found in koa forests. Researchers have not discovered what circumstances trigger the occasional explosions in this moth population.

The first outbreak documented in writing occurred in 1892. But oral accounts indicate similar events occurred before.

Based on data from previous outbreaks, it is possible this outbreak will spread to other areas of Hawaii island, although the exact path is unpredictable, DLNR said.

"Mapping the boundaries of this infestation will tell us what areas are affected right now, and provide a way for us to measure movement of the moths into new forest areas," said Roger Imoto, DLNR Division of Forestry and Wildlife administrator. "We want to assure the public that this is a natural phenomenon, and DLNR and its partners are actively monitoring. The public can help us by calling DOFAW if new areas are observed."

The department is asking people to report koa defoliation and increased caterpillar or moth abundance observed outside the Hilo and Hama­kua areas. Call 587-0166 or email dlnr@hawaii.gov with the nearest street address, date of sighting, and description of the defoliation. The public is also urged to send photos of defoliated areas.

For more information on the koa looper, visit www.hawaii.gov/dlnr/dofaw.

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The Associated Press contributed to this report.