Department of Agriculture

HONOLULU – The Hawai`i Department of Agriculture (HDOA) has begun a biological control program that releases a tiny parasitic insect to control the stinging Nettle Caterpillar.  The release of the natural enemy follows six years of extensive research that HDOA’s Plant Pest Control Branch has been conducting to assure that the natural enemy only affects the nettle caterpillar and no other native or beneficial insects or plants. Initial releases were on O`ahu, but staff will be making releases on Hawai`i Island and Maui soon.

“The detection of nettle caterpillar in Hawai`i quickly set HDOA on a mission to find a natural enemy that would be specific to that particular pest,” said Sandra Lee Kunimoto, Chairperson of the Hawai`i Board of Agriculture.  “Although this pest was not well known in the world, our entomologists were able to find and test a tiny wasp that preys on the stinging caterpillar and nothing else found in Hawai`i.”

“The way classical biocontrol works is that the population of the natural enemy will rise and fall with the population of the target pest,” said Neil Reimer, PhD., manager of HDOA’s Plant Pest Control Branch. “It will not totally eradicate a pest, but control it to a point where it is no longer a pest. It taps nature’s way of balance in the environment.

“We had several biocontrol projects running concurrently, including the highly successful biocontrol program for the Erythrina gall wasp that has resulted in the rebounding of the native wiliwili trees and a pending program to help ranchers control fireweed, a weed pest that is toxic to cattle,” Reimer added.

Environmental assessments were conducted and the appropriate permits were obtained from the U.S. Department of Agriculture in Riverdale, MD. Due to the success of Hawai`i’s biocontrol programs, the state has become a leader in the world on the use of biological control to fight invasive pests.

The Nettle Caterpillar (Darna pallivitta) was first detected at a plant nursery in Pana`ewa on Hawai`i Island in 2001 and are believed to have arrived on Rhapis palm seedlings imported from Taiwan.  Since then, its population has spread throughout Hawai`i Island, as well as areas on Maui and O`ahu.  Nettle caterpillars grow to about one-inch long, white in color with black bands.  The caterpillar has distinct bristly spines that when touched, may cause a burning sensation that lasts about an hour.  The caterpillar has been found primarily on the underside of the leaves of palm plants, grasses and lilies. (See Pest Advisory at:  https://hawaii.gov/hdoa/pi/ppc/npa-1/npa01-03_netcat.pdf )

The natural predator that is being released is a stingless tiny parasitic wasp, Aroplectrus dimerus, which was found parasitizing nettle caterpillars by a HDOA entomologist who was searching for natural enemies in Taiwan in October 2004. The predator wasp lays its eggs on the larvae of the nettle caterpillar and when the eggs hatch, the wasp pupae feed on the nettle caterpillar larvae. The natural predator measures about the size of a small gnat and while it is considered a wasp, it does not harm humans or other animals.

HDOA’s entomologist collected samples of the natural enemy and sent them to HDOA’s Insect Containment Facility in Honolulu where tests were conducted under quarantine conditions to determine if it would attack any other species in Hawai`i.  The tests indicated that the wasps would feed only on nettle caterpillar larvae.    There were other predators of the nettle caterpillar that were tested in quarantine, but were rejected as candidates for release because they also attacked other beneficial and native insects.

HDOA also consulted on this project with entomologists at the Smithsonian Institution, National Museum of Natural Science in Taiwan, and the Chinese Academy of Sciences (Institute of Zoology) in Beijing, Peoples Republic of China.

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