Photo 2. Close-up of Photo 1 to show the galls - gross distortions of the leaves and petioles of Erythrina variegata.
Photo 3. Dieback of Erythrina variegata caused by the Erythrina gall wasp, Quadrastichus erythrinae.
Erythrina gall wasp
Worldwide. Asia, Africa, North and South America (restricted), the Caribbean (restricted), Oceania. It is reported from Fiji, Samoa, and Tonga. It is thought to be from East Africa originally.
Erythrina variegata, and other Erythrina species. There are more than 100 species worldwide in tropical and sub-tropical countries, and they are used as ornamentals, living fences, and also as shade trees for coffee and cocoa, especially as their roots form nitrogen-fixing nodules with Rhizobium bacteria.
The wasp lays its eggs in the youngest leaves and stems. As the larvae hatch they cause the galls to develop. The leaves become swollen and deformed, and look unlike the leaves of healthy trees (Photos 1&2). Repeated attacks cause dieback and death (Photo 3).
The larvae pupate in the swollen tissues, and the adults cut holes in the leaves and stems to emerge (Photo 4). The wasps are 1-1.5 mm in length, with the female being larger than the male (Photo 5). The life cycle is about 20 days.
Spread over short distances is by flight, on the wind, and perhaps on clothing. Spread over long distances is thought to be on fallen leaves perhaps on boats or planes.
The damage is severe. Trees are defoliated by the gall wasp and often die as cycles of regrowth and attack result in loss of reserves. Erythrina seedlings are killed by infestations and this threatens stands of the tree. For example, in Hawaii about 95% of the Erythrina sandwicensis (wilwili tree) and Erythrina variegata - important trees in the endangered lowland dry forest - have been killed by the gall wasp.
Look for the mass of distorted swollen shoots on Erythrina trees, and seedlings, and trees that show die back.
After extensive search for parastioids in Africa and testing, scientists in Hawaii selected Eurytoma erythrinae to have the potential to bring the gall wasp outbreaks under control. Tests showed that it was a specific parasitoid of the gall wasp. Releases began in 2008, and have shown a substantial decrease in gall wasp populations. Importantly, Erythrina trees recovered with the production of healthy leaves and full canopies, although flowers of Erythrina sandwicensis still show damage. Another biocontrol agent may be released in future.
No control measures are recommended. Pruning has been tried, but was not successful. It is important, however, not to move Erythrina plants between localities where the gall wasp is present and where it has not yet established.
Injection of imidacloprid has been trialed, and is only recommended for highly valued ornamental trees because of the cost of this method.
AUTHOR Grahame Jackson
Information from Heu RA, Tsuda DM, Nagamine WT, Yalemar JA, Suh TH (2008) Erythrina erythrinae Kim (Hymenoptera: Eulophidae). New Pest Advisory. No. 05-03. State of Hawaii, Department of Agriculture; and from CABI (2015) Quadrastichus erythrinae (Erythrina gall wasp) Crop Protection Compendium (www.cabi.org/cpc). Photos 1&2 Albert (Bud) Mayfield, USDA Forest Service, Bugwood.org. Photo 3 Albert (Bud) Mayfield, USDA Forest Service, Bugwood.org. Photo 4 Richard Markham, ACIAR, Canberra. Photo 5 Erich G. Vallery, USDA Forest Service - SRS-4552, Bugwood.org.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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