How did parasitic wasps save native wiliwili trees in Hawaii from extinction? : Big Island now

A new animated video highlights the success story of how biocontrol, a process that uses a carefully selected living organism to control an invasive species, helped save the native Wiliwili tree from extinction.

The video, produced by the Hawaii Department of Forestry and Wildlife in collaboration with the Alien Pest Coordination Group, also shows how biological control can continue to be an important tool in managing invasive species in the state.

The native Wiliwili tree in Hawaii was saved from extinction through biocontrol using small parasitic wasps that prey on the gall wasp. Photo Courtesy: Department of Land and Natural Resources

In 2005, a new pest, the Erythrina gall wasp, made its way to Hawaii and quickly spread throughout the state, killing or severely damaging nearly all wild Wiliwili populations.

“The sudden arrival of the Erythrina gall wasp caught us all by surprise,” said Chipper Wichman, president of the National Tropical Botanical Garden. “Wiliwili is a key species in our dry forests and almost every part of this particular tree is used by cultural workers. The loss of this species would have had a profound impact.”

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In 2008, after extensive reconnaissance in Africa for predators of the gall wasp and testing to ensure these predators were not affecting other species, scientists were able to safely release a biocontrol agent: an even smaller parasitic wasp preying on the gall wasp.

The biocontrol agent successfully reduced the number of wasps to a level that did not kill the wiliwili trees and saved them from extinction.

Wiliwili is a keystone species in the dry forests of Hawaii, and almost every part of this particular tree is used by cultural workers. Photo Courtesy: Department of Land and Natural Resources

“Invasive species cost the state millions by reducing watershed benefits, degrading agricultural land, threatening human infrastructure and being a major cause of loss of biodiversity and native ecosystems in our state,” said Rob Hauff, a state official protection forester “Biocontrol has proven to be a safe, inexpensive and indispensable tool. The success of the Wiliwili gall wasp biocontrol is an example of what we can expect as we continue to support this type of work.”

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Before releasing a biocontrol agent, researchers conduct years of exploration and analysis to ensure it does not affect species other than the invasive target species. Proposed organic controls are also subject to careful scrutiny by specialists, regulators and the public.

Since the focus on safety was introduced in Hawaii in the 1970s, the biocontrol program has had an excellent record, according to the state Department of Land and Natural Resources, with no untargeted biocontrol harms unleashed in the past 50 years.

Given the ongoing impact of many invasive species currently in Hawaii, new, upgraded facilities are needed to expand biocontrol research capacity.

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A coalition of state and federal agencies — including the Department of Land and Natural Resources, the Hawaii Department of Agriculture, the University of Hawaii and the U.S. Forest Service and Agricultural Research Service — are currently discussing options for new facilities that can serve Hawaii and other neighboring islands in the Pacific, often associated with similar invasive species.

There are new biocontrol agents that may be ready for release in the near future. Two insects including a caterpillar that feed on the weed Miconia (Miconia calvescens) and a beetle perched on the weed tibouchina (Tibouchina herbacea), could be ready for release in Hawaii within the year.

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