A hiker in a healthy koa forest would normally be hard-pressed to see a single koa looper, entomologist Cynthia King says.
But these days, in areas of Hamakua and Hilo between the 2,000- and 4,000-foot elevation, a hiker might see hundreds of the native caterpillar.
“They’re present in the environment all year round,” said King, who works for the state Department of Land and Natural Resources Division of Forestry and Wildlife. There are “slightly higher numbers in the spring and summer.”
That makes right now a time when residents would be less likely to see the caterpillar, or the moth it becomes, King said. But in some Hamakua and Hilo koa forests, King observed as many as six to eight caterpillars on a single leaf, with entire branches with leaves turning brown from the defoliating effects of the insect.
The impacted area is about 24,500 acres, DLNR said, and is the largest koa defoliation in written history. Officials said based on data from previous outbreaks, this incident could spread throughout the island, although the path an expansion would take is unpredictable. The first written documentation of an outbreak was in 1892, but oral accounts indicate outbreaks before then. DLNR said researchers do not yet know what triggers the population explosions.
King said previous, similar increases in the numbers of koa loopers on koa trees on Maui haven’t caused permanent damage to the koa forests; most forests, she added, made a 100 percent recovery. DLNR studied those outbreaks, and in 2004 and 2009, saw 35 percent tree mortality in unhealthy forests. The koa looper did not seem to increase population significantly above the 5,000-foot elevation, either, she said.
“Because it’s a native moth and a native tree, we are not recommending any treatment at this time,” she said.
DLNR officials do want to learn more about the koa looper, what might be causing the occasional increase in population and how the moth and tree have evolved to interact, King said.
“We’ve only had the opportunity to observe them a couple of times at this point,” she said. “This is a really good opportunity for us.”
King said she did not recall any incidents of increased moth populations in Kona, although there was an outbreak recorded on Mauna Loa in the 1950s.
DLNR officials ask the public to report any incidents of increased moth populations by calling 587-0166 with information on the nearest street address, date of sighting, and a description of the defoliation.
The public is encouraged to send photos with location information to DLNR@hawaii.gov.