New threat to crops packs a nasty sting
By Kevin Dayton
Advertiser Big Island Bureau
HILO, Hawai'i — The nettle caterpillar, an alien pest with a mean sting and an appetite for some of Hawai'i's nursery crops, is expanding its territory on the Big Island.
A. Hara • Special to The Advertiser
Scientists say the caterpillar has been found at a number of sites within a 4-mile radius of the Pana'ewa farm outside of Hilo where it was first discovered in September 2001.
Spines of the nettle caterpillar release a venom when touched. The moth larva, about 1-inch long, devours ti, banana and other plants.
"I think this is a more serious problem than the coqui frog," said Arnold Hara, an entomologist with the University of Hawai'i's College of Tropical Agriculture and Human Resources. The noisy coqui is a nuisance, but the nettle caterpillar presents a health issue because of its painful sting, he said.
The caterpillar has infested about a half-dozen Pana'ewa farms and plant nurseries where growers are spraying to control it.
The nettle caterpillar also could hurt the visitor industry if it continues to spread, Hara said. "The coqui will disturb their sleep, but with this caterpillar — it hurts," he said.
The scientific name for the caterpillar is Darnapallivitta. The larva grows to up to an inch long and is covered with bristles that release a venom when touched.
Pana'ewa farm workers first learned the caterpillar had arrived two years ago when they were stung while handling palms and felt an itching and burning sensation.
The caterpillar is native to Southeast Asia and has a voracious appetite. Hawai'i researchers have identified two dozen local plant hosts that it feeds on, including dracaena, mondo grass, coconut and several other palms, ti and banana, said Stacey Chun, Hara's research assistant.
Chun described the caterpillar's sting as "just like a red-ant sting or bite, but it lasts maybe a week."
In its life cycle, Darnapallivitta takes an average of 80 days to develop from egg to caterpillar to an adult moth. Each female adult is capable of laying almost 500 eggs. So far, scientists have identified no natural enemies of the caterpillar in Hawai'i that could help keep its numbers in check, Chun said.
Researchers, including state Department of Agriculture entomologist Patrick Conant, have found the caterpillar on both sides of Hawai'i Belt Road where the highway bisects the Pana'ewa Forest. The pest has been trapped as far away as the Hilo Municipal Golf Course at the edge of urban Hilo.
Experts have been monitoring Pana'ewa plant nurseries and other areas, but Chun said it's possible that the pest is multiplying and has gone undetected in the surrounding rain forest. Hara said the caterpillar has not been found in Kea'au.
The pest has at least two efficient ways of expanding its territory: The adult moths can fly off to deposit their eggs, and the microscopic eggs may be moved from place to place on potted plants.
Researchers are attempting to locate natural enemies of the caterpillar in Indonesia that can be safely imported. Hawai'i doesn't have any native insects in this caterpillar family, so there is a good chance there are parasites that will attack the nettle caterpillar without harming native species, Hara said.
Scientists settled on biological control as the best way to fight the caterpillar because stopping its spread would be very difficult given its distribution today, Hara said.
"It could probably be on other islands or on the other side of the island and we don't know about it," he said. "It could easily be on a plant or somewhere else and we're not going to find out about this caterpillar until a year from now."
Hara is working with the state Department of Agriculture under a three-year, $187,000 grant from the U.S. Department of Agriculture Tropical and Subtropical Agricultural Research program to study the pest.
Reach Kevin Dayton at kdayton@honoluluadvertiser.com or (808) 935-3916.
