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 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). Within a few years, the wasp had been found from the Indian Ocean (India, Singapore, Mauritius and Reunion) and Asia (Singapore, Taiwan, Hong Kong, China, the Philippines, Okinawa) across the Pacific to American Samoa, Guam and Hawai`i (Reimer 2007; CABI website). The wasp was detected in Miami, Florida in autumn 2006 (Anon. 2006).

The Erythrina gall wasp was discovered on Oahu in April 2005 and shortly afterwards found on all the major Hawaiian islands (Reimer 2007).

Twenty-four species in the genus Erythrina had been documented as hosts (Fulton, pers. comm., 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). Widespread infestations were observed by September 2005 (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 (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 was not then known (Wright, pers. comm. 2005); While systemic insecticides such as imidacloprid can be effective in treating landscape trees, the approach is not considered sustainable for protection of native wilwili trees, owing to costs and difficulty in accessing tree populations to treat them repeatedly (Wright, pers.comm. 2018)

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. A promising candidate – a previously undescribed wasp, Eurytoma erythrinae  – was collected in South East Africa from South Africa and Mozambique to Tanzania in 2006. After testing for host specificity (Reimer 2007), the Eurytoma wasp was approved for release in 2008 (Ohira 2008). Preliminary results were encouraging. At the Pu`u-o-kali preserve on the dry side of Maui, mature trees sprouted leaves and numerous seedlings appeared where there had been none (Madeiros pers. comm. April 2010). However, a dozen years later it is observed that only half of the mature trees are setting seed due to continued formation of wasp galls on flower buds and predation by the seed beetle.

Scientists are now testing a second biocontrol agent, Aprostocetus sp. which will hopefully be released soon.  It is expected to contribute to reducing the persistent gall wasp damage to flowers and seed pods on wilwili trees (Wright, pers. comm. 2018).

Recovery of the tree continues to be hampered by the other threats, including inability of seedlings to survive in areas invaded by alien grasses and prone to fire. Even mature trees that have been attacked by the gall wasp are more vulnerable to fire.

The gall wasp also caused considerable damage to urban plantings of exotic coral. In the early stages of the invasion, the Department of Parks and Recreation of the City and County of Honolulu removed about 1,000 dead erythrina trees at great expense (Reimer 2007). Scientists are trying to breed Erythrina trees resistant to the gall wasp for landscape use (Wright pers. comm. 2018).

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). The erythrina gall was detected in Brazil in 2014 (   and Mexico in 2017 (Palacios-Torres et al. 2017).

USFS scientists and managers developed a conservation priority-setting framework for forest tree species at risk from pest & pathogens and other threats. The Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) uses FIA data and expert opinion to group tree species under threat by non-native pests into vulnerability classes and specify appropriate management and conservation strategies. The scientists prioritized 419 tree species native to the North American continent. The analysis identified 15 taxonomic groups requiring the most immediate conservation intervention because of the tree species’ exposure to an extrinsic threat, their sensitivity to the threat, and their ability to adapt to it. Each of these 15 most vulnerable species, and several additional species, should be the focus of both a comprehensive gene conservation program and a genetic resistance screening and development effort.  Erythrina gall wasp is not known to be a threat to any of these 15 most vulnerable species. 

Sources

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

CABI website: https://www.cabi.org/isc/datasheet/46220

Culik, M.P., D. dos Santos Martins, J. Aires Ventura and V. Antonio Costa. 2014. The invasive gall wasp Quadrastichus erythrinae (Hymenoptera: Eulophidae) in South America: is classical biological control needed? https://www.tandfonline.com/doi/abs/10.1080/09583157.2014.900735

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.

Palacios-Torres, R.E., J. Malpica-Pita, A.G. Bustamante-Ortiz, J. Valdez-Carrasco, A. Santos-Chávez, R. Vega-Muñoz and H. Vibrans-Lindemann. 2017. The Invasive Gall Wasp Quadrastichus erythrinae Kim in Mexico. Southwestern Entomologist. http://www.bioone.org/doi/abs/10.3958/059.042.0405

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/

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. 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.