Watching for Wiliwilis

It was a pleasant spring day in Hawaii as we reached the end of Kokonani Street. Just ahead was the remnant of the last volcanic action on Oahu: Koko Crater. Mike Letzring, collections manager at the San Diego Zoo, and I greet the security guard and enter Koko Crater Botanical Garden.

The wonderful smells of plumerias engulf us as we walk along the dry path. We continue past the towering plumerias and pass cacti and succulents from the Americas, and impressive baobabs from Africa – all plants that thrive in the hot dry climate inside this massive crater.

As we round the next corner in the path, we see before us a large stand of native trees, the trees we came to see – Erythrina sandwicensis more commonly called the wiliwili tree.

In 2005, an unwanted guest hitched a ride to the Islands; a tiny insect called the Erythrina gall wasp (EGW). It invaded Hawaii and decimated thousands of native and non-native Erythrina trees and left others with leaves gnarled and misshapen. After three years of research and testing, a predator Eurytomid wasp was approved for release and slowly spread throughout the islands, keeping the EGW in check and lessening its destruction.

We saw the damage first hand in 2007 and now, in 2011 we wanted to see how the trees were fairing. I stood before the stand of wiliwilis and saw some newly downed trees, a reminder of the damage the tiny insect. Red, bean-like seeds were scattered over the ground and as I looked closer, I saw new seedlings emerging under the protection of the mother tree above, replacing those lost to the pest.

We walked around the native stand of trees and, with permission, collected a few seeds for ex-situ conservation at the San Diego Zoo along with leaf samples for DNA barcoding. On one of the largest trees, a plaque told the story of the wiliwilis and documented them as protected by State law under the Exceptional Tree Act 105.

As I turned to leave, I looked above the treetops and could see the top of crater ridge and a beautiful blue sky.

Erythrina sandwicensis was one of many Erythrinas we saw on our trip to Hawaii; Waimea Valley, National Tropical Botanical Garden, Lyon Arboretum, and Foster’s Botanical Garden are all homes to beautiful coral trees from around the world. The San Diego Zoo is collaborating with these institutions and others to propagate rare Erythrinas and protect them in ex situ conservation facilities as part of a grant funded by the Association of Zoological Horticulture (AZH).

While in Hawaii, we documented many Erythrinas in bloom with minimal gall wasp damage and collected leaf samples from 64 species for DNA barcoding. Back in San Diego, I am working with Heidi Davis and the genetics division at the Institute for Conservation Research to extract, purify, and sequence DNA from leaf samples for species identification. This will also help us propagate and manage the Erythrinas in our collection.

Christy Powell is the Plant Propagator and Erythrina Collections Specialist at the San Diego Zoo and Conservation Chairperson for the Association of Zoological Horticulture.