Wiliwili

Erythrina coral trees can be found throughout the tropics. They are salt tolerant, and often grow in dry coastal areas.

The wiliwili, Hawaiian coral tree (Erythrina sandwicensis), is an endemic species. It grows to be a large tree with a height of up to 60 feet (20 m). It thrives in the hot dry lowlands of the Islands. It has a reputation for being an extremely resilient tree, able to withstand extreme physical damage and drought. The wiliwili is one of the few deciduous trees in the Hawaiian Islands and may lose its leaves during the dry season.

The Hawaiian name wiliwili means to twist. It describes the twisting corkscrew shaped seed pods. The seed pods contain 1-3 jewel like seeds, that vary in color from purple, red, yellow green, and white. The hard buoyant seeds can float in the ocean and remain viable for up to a year. The hard durable seeds are used to make beautiful lei. The flowers also come in a multitude of colors. Sometimes multiple colors bloom on the same tree.

Hawaiians used the buoyant wood as a float for nets and outrigger canoes. Wiliwili wood was especially desirable for making surfboards.

The willwili was almost pushed to extinction when the Erythrina gall wasp (Quadrastichus erythrinae) was discovered on O‘ahu in 2005. The wasp quickly spread to all of the major Hawaiian Islands. Hawai‘i was only one of many places where the tiny wasp from east Africa invaded in the early 2000s.

The parasitic Erythrina gall wasp injects its eggs into the leaves and stems of the wiliwili tree. The developing larvae induce the formation of galls which deform the leaves. Severe infestations can kill trees.

After years of study, scientists were able to save the wiliwili by introducing the Tanzanian parasitoid wasp, which specifically targets the Erythrina gall wasp. One of the benefits of using parasitic biological controls is that the two populations are complimentary, which reduces the risk of non-target species being affected.

Early attempts at introducing biological controls to the environment have taught us many valuable lessons about their potential dangers. The parasitic fly Trichopoda pennipes, was introduced to Hawai‘i to control the southern green stink bug in the 1960s. The endemic koa bug is also a kind of stink bug, and fell prey to the parasitic fly as well.

Biological controls for invasive species are studied much more extensively before releasing them today than in the past. This makes progress toward controlling invasive pests frustratingly slow for some. However, careful study reduces the risks of unintended consequences.

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