Hawaiian officials from the state Department of Agriculture and Department of Land & Natural Resources plan to release a wasp to combat another wasp that is killing native williwilli trees.
Erythrina gall wasps are a mostly yellow, 6- to 8-millimeter-long invasive pest that create galls in erythrina tree tissue that serve as cocoons for their larvae to mature. The galls deform leaves and interfere with the plant’s ability to take in water and light.
The Eurytoma wasp, called “a gall wasp gladiator” by the U.S. Department of Agriculture, was released in Hawaii in 2008 to destroy the galls in the native trees.
Female Eurytomas deposit eggs inside galls. When they hatch, the young gladiators eat gall babies still inside the cocoons. Then, the wasps can tunnel to up to four nearby galls and feed on those larvae.
More than 8,000 individuals were initially released at sites on Oahu, Maui, Kauai, Hawaii island and Molokai. Within a few months, the gladiator was established and wiliwili trees began to recover and show “healthy, non-galled new leaves and vigorous overall growth.” After the second year, more than 60 percent of young shoots were damage-free and by 2011, 90 percent of the targeted sample wiliwili trees had “full canopy coverage.”
Unfortunately, the gladiator wasp only goes after larger galls and not smaller ones formed on flowers, seed pods, and seedlings. More recent studies show that 54 percent of wiliwili seeds sampled after the release failed to form viable seeds as a result of gall wasp damage.
To help the Eurytoma wasp the state Department of Agriculture and Department of Land & Natural Resources want to send a backup wasp called Aprostocetus nitens.
The backup insect is a parasitoid wasp and only use one host to complete its development. Aprostocetus nitens are able to live on smaller galls. Eggs of the parasitoid wasp can’t develop unless they are inside the Erythrina gall wasp.
Studies indicate that the gladiator and its potential backup wasp do not have negative interactions with Hawaii’s environment, or with one another.
The state DOA is asking to release Aprostocetus nitens as a supplement from containment into the natural environment. Mature adults would be released on severely infested trees first. They plan to release thousands of new wasps until the species is established.
A public comment period for the state Department of Agriculture draft environmental assessment will remain open until Jan. 22.