Department of Agriculture

HONOLULU – The Hawai`i Department of Agriculture (HDOA) today released the first batch of tiny insects that are natural enemies of the Erythrina Gall Wasp (EGW), the insect that has devastated wiliwili and coral trees across the state.  Staff from HDOA’s Plant Pest Control Branch released about 500 tiny wasps called Eurytoma erythrinae, in a stand of native wiliwili trees in Liliuokalani Botanical Gardens in Liliha.  About a dozen such releases will be taking place on each island statewide.

“The release of this natural predator of the erythrina gall wasp is the only lifeline for our native wiliwili trees,” said Sandra Lee Kunimoto, Chairperson of the Hawai`i Board of Agriculture.  “Finding this biological control agent and making sure that it will not cause harm to other plants or beneficial insects in Hawai`i has been a priority for our staff since the discovery of the gall wasp here in 2005.”

EGW was first detected in Manoa in April 2005 by a University of Hawai`i researcher.  By the time EGW was detected, it has been widely established on Oahu and spread rapidly to neighboring islands.  It is not known exactly how EGW arrived in Hawai`i, but it is suspected that it arrived through Southeast Asia.

Adult EGW lay its larvae in the leaves of erythrina trees, which include native wiliwili and other introduced species such as coral trees and the tall erythrina that were widely used as windbreaks.  The larvae cause severe galling or deformities in the leaves and eventually the leaves drop off.  Without its leaves, the tree is not able to derive much energy and will eventually decline in health and die.

“Finding this natural predator of the erythrina gall wasp has been a priority for our branch since it threatened our native wiliwili trees,” said Neil Reimer, manager of the Plant Pest Control Branch.  “Biological control of this pest is the only way to save the wiliwili in remote and forested areas.

“This is actually the perfect time to release this biocontrol, because the young leaves are just emerging and as the gall wasp population increases, so will the predatory wasps,” Reimer added.

The biocontrol wasp lays its eggs next to the EGW eggs on the leaves and when the larvae emerge, the biocontrol wasp larvae preys on the EGW larvae. 

HDOA’s exploratory entomologist, Mohsen Ramadan, collected the biocontrol wasp in Tanzania in 2005, where the EGW is native.  Because EGW is not a problem in its native range, it was apparent that biological control of the pest is controlling EGW populations. Ramadan spent several months in 2005 and in 2007 in areas of Africa collecting and shipping insects back to HDOA’s quarantine facility.  A team from the University of Hawai`i College of Tropical Agriculture and Human Resources also traveled to Africa to aid in the search.  (Ramadan is currently back in Africa collecting potential biocontrol agents for other invasive weeds including fireweed, fountain grass and ivy gourd.)

Once the samples from Tanzania were received in Honolulu, HDOA insectary staff began rearing the insects in quarantine and conducted host-specificity testing, which tests whether the potential biocontrol agent will attack other beneficial insects or plants.  Research showed that the biocontrol insects were specific in its attack on EGW. Permits to release the biocontrol insects were obtained from the Hawai`i Department of Agriculture in 2007, and the permit from the U.S. Department of Agriculture about a week ago.

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For more information on EGW, click here.