New wasp could help to protect crucial native trees
State hopes to deploy second insect to fight destructive galls
Reinforcements are being called to the front lines of a wasp-on-wasp war that has native wiliwili trees in Maui County and on other Hawaiian Islands hanging in the balance.
Officials are asking that a new wasp be deployed throughout the state to back up a “gladiator” wasp released more than a decade ago in an effort to find and destroy gall wasps, a bad cousin that has damaged and killed thousands of wiliwili, along with other important trees.
The state Department of Agriculture and Department of Land & Natural Resources biological control plan is detailed in a recent draft environmental assessment that’s needed to get state and federal permits for the new insect’s release.
Erythrina gall wasps, mostly yellow, 6- to 8-millimeter-long invasive pests, create galls — swollen, tumor-like growths — in erythrina tree tissue that serve as cocoons for their larvae to mature. These tumors deform leaves and interfere with the plant’s ability to take in water and light, eventually killing it.
Dubbed “a gall wasp gladiator” by the U.S. Department of Agriculture, the Eurytoma wasp, a black, 2-millimeter long wasp, was collected from Tanzania, “rigorously” tested and released throughout the state in November 2008.
Much like a science-fiction film, female Eurytomas deposit eggs inside galls. When hatching, the young gladiators eat gall babies still inside the cocoons. Then, they tunnel to up to four nearby galls and feed on those larvae.
Experts, such as Maui-based biologists Forest and Kim Starr, said in the state EA that they consider the Erythrina release to be a successful form of biocontrol for the state.
The report said more than 8,000 individuals were initially released at sites on Oahu, Maui, Kauai, Hawaii island and Molokai. Within 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.”
However, the gladiator wasp 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.
Enter Aprostocetus nitens. The small (1.1 to 1.7 millimeter long), shiny black and metallic green wasp, comes from gall wasps’ motherland of Africa. It doesn’t need to have a male for fertilization and offspring. And, it can survive four days without food, living on average 120 days.
Unlike the gladiators, the parasitoid wasp uses only one host to complete its development and is able to live on smaller galls. Eggs of the parasitoid wasp can’t develop unless they are inside the Erythrina gall wasp, according to Lissa Fox Strohecker, Maui Invasive Species Committee spokeswoman.
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 A. nitens as a supplement from containment into the natural environment. Mature adults would be released on infested trees, with inoculations focused on severe infestations first.
The department expects to rear and release thousands of these supplemental wasps until the species is established, and no particular timing of release is planned, the report said.
Gall wasps were first discovered on Oahu in 2005. They spread quickly throughout the state and resulted in the defoliation and death of thousands of Erythrina trees.
“We don’t know exactly how the gall wasp made it to Hawaii in the first place — it is found in Taiwan and likely hitchhiked in material imported to Hawaii,” Strohecker said. “It spread quickly, aided by winds and accidental movement along roadways and devastated the native wiliwili as well as the non-native Erythrina planted as windbreaks, such as along the old Mokulele Highway near Kihei.”
Wiliwili in bloom, with its coral red and salmon-colored flowers, is distinctly Hawaii. The native plant is vital both ecologically and culturally. Native Hawaiians value red wiliwili seeds for lei making among other uses, the report said.
Strohecker added that wiliwili are key to the survival of drylands forests on the leeward slopes of Maui.
“Only 3 percent of this forest remains and the loss of the pillar species of this ecosystem further jeopardizes the chances of survival of the plants and animals that live in the dryland ecosystem,” she said.
The largest populations of wiliwili on Maui are in Kaupo and Nuu through Ulupalakua and Puu o Kali above Kihei. Also, trees are scattered in West Maui, according to Strohecker.
The state, along with report experts, echoed that more must be done to aid an already beneficial biocontrol effort to salvage wiliwili.
“If nothing is done, wiliwili could continue to decline due to their inability to produce viable seed,” the report said.
Strohecker said the state DOA is “thorough” in evaluating and testing for the reliance of the biocontrol on the host species. She praised the efforts and said she supports the proposed release.
“The first biocontrol is the reason you can see wiliwili trees today — a second biocontrol to help further wiliwili’s survival is fantastic,” she said.
Deadline for comments on the state DOA draft environmental assessment is Jan. 22. For submissions, contact Danielle Frohlich at SWCA Environmental Consultants by email at Dfrohlich@swca.com, by phone at (808) 548-7922 or by mail at 307a Kamani St., Honolulu 96813.
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