June 17, 2010 – Kurtistown, Hawaii

Video by David Corrigan

Meeting in a Puna plant nursery, state agriculture officials released a stingless wasp from Taiwan on Wednesday, the latest recruit in the Big Island’s battle against the stinging nettle caterpillar.

The caterpillar, also native to Taiwan, is believed to have arrived on Hawaii Island in 2001, hitched to a shipment of palm seedlings that were found in a Panaewa nursery. Since then, the caterpillar has spread across the island – and to parts of Oahu and Maui – grinding island foliage and stinging hapless gardeners.

The wasp was discovered – as HDOA entomologist Pat Conant explains in this video – through the hard work of Larry Nakahara, the now retired former ag boss, who went to Taiwan to hunt down the caterpillar’s natural enemy.

The wasp, Aroplectrus dimerus, is host specific to the stinging caterpillar. The Hawaii Department of Agriculture says the predator wasp – which is the size of a gnat and is of no harm to humans – 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 wasp will not eradicate the caterpillar, but rather reduce their numbers to make them manageable.

HDOA says its entomologist collected samples of the wasp in 2004 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 Hawaii. HDOA says 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.