INVASIVE SPECIES: Erythrina gall wasp (Quadrastichus erythrinae)

Damage on wiliwili by Erythrina gall wasp (EGW)

  • Erythrina gall wasp (EGW) is a destructive pest to Erythrina species, including Hawaii’s native wiliwili trees (Erythrina sandwicensis). It is a gall-forming eulophid wasp, which inserts its eggs into young leaf and stem tissue and forms galls, which result in a loss of growth and vigor, and sometimes defoliation and death of the host tree. Eurytoma erythrinae, a wasp native to Africa (Tanzania), was first released as a biocontrol agent targeting EGW in November 2008 and has significantly reduced the gall wasp infestations. The release resulted in a significant reduction in EGW populations and recovery of wiliwili trees throughout the state, however, ongoing monitoring of wiliwili has shown that inflorescences and seed pods are still being negatively affected by the gall wasp. The new proposed agent it is able to live on much smaller galls, such as those found in flowers, seed pods, and young seedlings, and will supplement the success of E. erythrinae in suppressing infestations of Erythrina gall wasp and improve the survival success of wiliwili.
  • Distribution: Erythrina gall wasp was discovered on Oʻahu in April 2005 and shortly after reported on the islands of Hawaiʻi, Kauaʻi, Maui, Molokaʻi, Kahoʻolawe, and Lānaʻi. It was first described in 2004 as a new species by Kim et al. from specimens from Singapore, Mauritius, and Reunion.

THE CANDIDATE: Aprostocetus nitens

Close up of EGW (Quadrastichus erythrinae)

  • Aprostocetus nitens is an ectoparasitoid proposed as a complementary biocontrol to E. erythrinae to reduce the gall wasp’s negative impacts further. Unlike E. erythrinae, this parasitoid utilizes only one host individual to complete its development, and, therefore, can live on much smaller galls, such as those found in flowers, pods, and young seedlings.
  • Native range: Aprostocetus nitens was first described in 2009 soon after it was discovered and collected in Tanzania during an exploratory survey for natural enemies of EGW.
  • Host testing results: Host specificity testing was completed at the Hawaiʻi Department of Agriculture Insect Quarantine Facility in 2009. Non-target gall-forming insects were the same used during trials of E. erythrinae; results indicate that A. nitens is host specific and has no preference for any of the seven non-target gall-forming species studied. Even if A. nitens were to parasitize these non-target species, it would be unable to produce any offspring because none of these species was shown to be suitable for supporting species’ development.

Timeline of project progress:

  • Host specificity testing completed.
  • Draft Environmental Assessment Published in OEQC’s The Environmental Notice for public comment on December 23, 2019. The 30-day comment period closed on January 22, 2020.

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