Erythrina Gall Wasp

adult erythrina gall wasps, male and female
Quadrastichus erythrinae
Last updated by:

Faith Campbell

NOTE: this pest is not known to spread in or on firewood. It is included in the Gallery of Pests for general information purposes only.

The wiliwili tree (Erythrina sandwicensis) is endemic to the Hawaiian islands. Like other dryland plants on the islands, the wiliwili faces numerous threats, including a non-native seed weevil, Specularius impressithorax (Hurley, 2005); fire – fueled in part by invading fountain grass; and feral ungulates (LaRosa, pers. comm., 2005). The latest threat is the Erythrina gall wasp (Quadrastichus erythrinae).

The Erythrina gall wasp was discovered on Oahu in April 2005 and shortly afterwards found on all the major Hawaiian islands (Reimer 2007). As of mid-2005, the wasp had been found from the Indian Ocean to Hawai`i, including Taiwan, India, Hawaii, Hong Kong, China, and the Philippines (Reimer 2007). Twenty-four species in the genus Erythrina had been documented as hosts (Fulton, pers. comm., 2005). By autumn 2006, the wasp was detected in Miami, Florida (Anon. 2006.) The wasp had been named only in 2004, by a scientist when examining specimens collected from dying coral trees in Singapore and the Mauritius and Reunion islands (Hurley, 2005).

In the United States, concern focuses primarily on the wasp’s damage to the native wiliwili, a tree of great societal, cultural (Hurley, 2005) and ecological importance. The state’s largest intact stands of native wiliwili are on Maui, where the wiliwili is the keystone species of the low dryland forest (Madeiros, pers. comm., 2005). By September 2005, widespread infestations were observed and the efforts to contain the gall wasp by pruning out infestations had not succeeded (Monson, 2005). By 2010, it was observed that wasp damage to the wiliwili was most severe at low elevations. Mature trees are dying, the biggest trees first (Madeiros pers. comm. April 2010). All seedlings had died and saplings were in steep decline at the reserve protecting the best remaining wiliwili ecosystem — Pu`u-o-kali (“hill of waiting”) (Madeiros pers. comm. April 2010).

Concerned Hawaiians initiated a suite of efforts aimed at protecting the endemic wiliwili tree. Scientists and private citizens began a program to collect seeds for preservation, with guidance from experts at the USDA National Center for Genetic Resources Preservation (formerly National Seed Storage Laboratory) in Ft. Collins, Colorado (Ellis, pers. comm. 2005; Reimer 2007). They also tried to protect trees through injection or soil drench with systemic insecticides. The efficacy of the insecticide over the long term is not yet known; in Taiwan, chemical controls have not proven effective. (Wright, pers. comm. 2005).

Scientists at the University of Hawai`i-Manoa (Wright, Rubinoff, and Bokonon-Ganta 2007) and Hawai`i Department of Agriculture (Loope pers. comm. January 2006) began the search for biocontrol agents. Since the gall wasp was believed to be African in origin, (La Salle, pers. comm., 2005) the search started in Tanazania. A promising candidate – a previously undescribed wasp in the Eurytoma genus – was collected in Tanzania in January 2006 and tested by HDOA for host specificity (Reimer 2007). The Eurytoma wasp was approved for release in 2008 (Ohira 2008). Preliminary results of the biocontrol effort are encouraging. At the Pu`u-o-kali preserve on the dry side of Maui, mature trees are successfully sprouting leaves and numerous seedlings have appeared where there had been none (Madeiros pers. comm. April 2010).

While the focus has been on threats to native tree populations, damage to urban plantings of exotic coral trees has caused significant economic impacts. The Department of Parks and Recreation of the City and County of Honolulu has removed about 1,000 dead erythrina trees at great expense (Reimer 2007).

Little concern has been seen in the U.S. mainland, although both native and exotic species in the Erythrina genus are found in mainland North American and – especially – in tropical America. There are two native Erythrina species in the southern United States: Erythrina flabelliformis is found in the Sonoran desert and E. herbacea ranges from Texas to South Florida and North Carolina. Seventy species could be impacted in the American tropics, such as native E. corallodendron, E. corallodendron var. connata, and E. eggersii (Loope, pers. comm., 2005).

 

Sources

Anonymous. 2006. Florida Department of Agriculture and Consumer Services. Erythrina Gall Wasp, Quadrastichus erythrinae Kim, in Florida. 25 October 2006

Ellis, David. 2005. Plant physiologist, U.S. Department of Agriculture, Agricultural Research Service. Personal communication. David.ellis@ars.usda.gov.

Fulton, Will. 2005. Horticulturalist, National Tropical Botanical Gardens – http://ntbg.org. Personal communication. wfulton@ntbg.org.

Hurley, T. 2005. Tiny wasp may kill off native trees. Honolulu Advertiser Newspaper. Thurley@honoluluadvertiser.com.

LaRosa, Anne Marie. 2005. Forest Health Coordinator, Institute of Pacific Islands Forestry, U.S. Department of Agriculture Forest Service. Personal communication. alarosa@fs.fed.us.

La Salle, John. 2005. Head of the National Australian Insect Collection, CSIRO Entomology. Personal communication. John.lasalle@csiro.au.

Loope, Lloyd. 2005 and 2006. Research Scientist, U.S. Geological Survey. Personal communication. Lloyd_loope@usgs.gov.

Medeiros, Arthur C. 2005 and 2010. Research Biologist, U.S. Geological Survey. Personal communication. acm@aloha.net.

Monson, V. 2005. Efforts to control erythrina gall wasps fail. The Maui News. vmonson@mauinews.com.

Ohira, R. 2008. Predator wasps released to save wiliwili trees. Honolulu Advertiser Newspaper. November 25, 2008.

Reimer, N.J. 2007. Hawaii Department of Agriculture. Field Release of Eurytoma sp. (Hymenoptera: Eurytomidae), for Biological Control of the Erythrina Gall Wasp, Quadrastichus erythrinae Kim (Hymenoptera: Eulophidae), in Hawaii. Draft Environmental Assessment.

Wright, Mark. 2005. Assistant Professor and Extension Specialist, University of Hawaii. Personal communication. markwrig@hawaii.edu.

Wright, M.G., D.Z. Rubinoff, A.H. Bokonon-Ganta. 2007. Proposal: Initial Exploration (in Africa) and Genetic Work to Accelerate Efforts at Biological Control of the Erythrina Gall Wasp Quadrastichus erythrinae Kim. For consideration for funding by Maui County.