Wiliwili (Erythrina sandwicensis) – Dodging a bullet

    In 2005, a tiny wasp from Africa was accidentally introduced to Hawai‘i. The Erythrina gall wasp (Quadrastichus erythrinae), no bigger than a grain of sand, attacks the leaves of both the native endemic wiliwili and introduced coral trees causing the leaves to deform and eventually fall off. Without healthy leaves for photosynthesis, thousands of wiliwili and coral trees have died since 2005.

    When it was realized that chemical or manual control of the gall wasp wasn’t very effective, hundreds of people began collecting thousands of wiliwili seeds for storage at Lyon Arboretum and other genetic safehouses. Meanwhile, the State Department of Agriculture (DOA) began its search for a biocontrol agent to counter the Erythrina gall wasp.

    In 2006, the DOA found a gall wasp assassin, another tiny wasp from Africa, Eurytoma erythrinae, that kills the larvae of the Erythrina gall wasp. After extensive testing to make certain the assassin wasp would only attack the gall wasp and not other native or important introduced insects, it was released in 2008 on Maui and later on O‘ahu.

    Since then the results have been dramatic. Wiliwili trees throughout the State rebounded, putting out fresh healthy leaves following the 2009 winter rains. Only time will tell how effective this little assassin will be in years to come but for now, it appears that this common and beautiful tree of Hawai‘i’s dry forests has dodged extinction’s bullet.

Habitat & Appearance: Often wiliwili are the largest trees (up to 50 feet tall) in Hawai‘i’s dry lowland forests and shrublands (on all eight main Hawaiian Islands). Yet, different populations of wiliwili vary greatly in stature, flower color (light green, yellow, red and, most commonly, orange), and seed size and color (pale yellow through orange to dark red). Most wiliwili have thorns but this too varies tremendously between trees with some being nearly thornless while others are a treehuggers nightmare. However, all the wiliwili I have ever seen have an orange tinge in their bark and few seeds (one to four) in their seedpods (two of the ways you can distinguish them from introduced Erythrina). Wili means "to twist," so, wiliwili is likely a reference to the way the pods twist as they dry to expose and release their seeds. Wiliwili drop their three-part leaves during the dry season to conserve water.

Wiliwili in Hawaiian Culture: Four sisters once lived in Ka‘u on the Big Island. The first, Moholani, was very beautiful. However, the second sister was bald, the third was humpbacked, and the fourth had ragged wind-tossed hair. Moholani married and had a son who was given to the gods to raise. One day Moholani’s husband was lured out to sea by sirens. Frantically, Moholani asked her sisters to help her find her husband. But they refused, calling him worthless. This aroused the wrath of Moholani’s son who sent lighting to transform the sisters into trees. The bald sister became a tree with few leaves, the humpbacked sister a tree with gnarled branches, and the sister with wind-tossed hair a tree with leaves that flutter in the wind. Chastened, Moholani’s husband returned, never to stray again. And, according to legend, this is how the wiliwili came to be. (Taken from Majesty The Exceptional Trees of Hawaii, 1982.)

    This is just one of many mo‘olelo (stories) concerning this commonly-known and useful tree. The lightweight wood was fashioned into long surfboards, canoe parts such as ama, and floats for fishnets. The seeds are still strung into colorful lei.

Collecting Seeds: Pua ka wiliwili nanahu ka manō; pua ka wahine u‘i nanahu ke kānāwai. (When the wiliwili tree blooms, the sharks bite; when a pretty woman blossoms, the law bites.) (Taken from ‘Ōleleo No‘eau Hawaiian Proverbs & Poetical Sayings by Mary Kawena Pukui, 1983.) Good advice for both young men competing for a beautiful woman and surfers who need to know how to tell the difference between the true Hawaiian wiliwili and the introduced Erythrina often incorrectly called wiliwili. The true wiliwili flowers in late summer and early fall when the ocean is warm and the sharks are mating (and aggressive). In contrast, the most common introduced Erythrina, Erythrina variegata, flowers during the winter months. This means that fresh wiliwili seeds are on the trees during the winter months. However, if it’s the wrong season, look down. Often seeds from previous years can be seen littering the ground beneath the tree. 

    When you get home, wash the seeds well to remove any dirt or small white spots; these are the eggs of a non-native seed weevil, Specularius impressithorax, that will bore into the seed and kill it. Look for borer holes and, then, place the seeds in a cup of water to see if they sink; discard any seeds that float or have holes. If you’re not going to germinate the seeds right away (within a month), dry and store them in your refrigerator where they will remain viable for ten years more – but, don’t forget to label them! 

Growing from Seed: Wiliwili seeds sprout quickly if scarified. You can soften the very hard seedcoat and make it easier to scar if you place the seeds in a shallow (1/2 in deep) pan of tapwater for a few days. Some seeds, particularly older ones, may begin to swell during this period; remove these and sow them before they color or release sugars, etc., into the water. Everyone has his or her favorite method of scarification. I prefer wet sandpaper but others like to use a sharp knife, a file, or nail-clippers. Whichever tool you use, the important thing is to get through the water-impermeable seedcoat without damaging the delicate embryo inside. Do this by avoiding the side of the seed with the hilum (the dark scar on the seed where it was attached to the pod). If you’re not sure you have adequately scarred the seed, place it back in the pan of water and look for blistering or swelling where you scarred it. If the seed looks unchanged after a couple of hours, take it out and scar it again.

    Wiliwili seeds are large. So, place the scarified seed in a deep (4-plus inches) starter pot about one inch below the surface of your favorite, new, clean potting media. (I always use new media for my seeds; old used media may contain fungus or bacteria that can attack and kill the vulnerable embryo.) Within a week, your wiliwili seedling should pop through the surface and start growing its first true leaves. If the pot is not already in a sunny place, move it; wiliwili seedlings grown in the shade will be lanky and have a tough time when you transplant them to your garden. 

Growing from Cuttings: I’m not a fan of growing wiliwili from cuttings (or air-layers) but it can be done. And, it’s particularly useful if you don’t want to wait years for your wiliwili to flower or make sure the flower color matches what you wanted.

    Take a 6-9 inch cutting from an actively growing branch and remove all but the terminal young leaves. Recut the stem base with a razorblade and dip or apply a rooting compound (e.g. Dip’nGrow®). Place the bottom half of the cutting in a rooting media of 100% perlite or 75% perlite, 25% vermiculite or peat moss. Place the pot under a mist system or inside a large, clear, slightly-vented container in bright but not direct sunlight. Rooting can take several months, so be patient. 

Growth in the Garden: Wait until the wiliwili seedling has developed several leaves and some bark at its base before planting it out in a site with full sun; this takes 2-4 months. Water the new plant initially once a week for a month or two and then stop. The plant should then be watered only occasionally if at all. Remember, this is a dry forest tree and if you water it too often you’re likely to kill it by encouraging fungal or bacterial diseases to attack its roots and truck.

    Wiliwili grows fast and can reach six feet in height in less than a year. Unfortunately, they are one native tree that takes several years to mature, so don’t expect to see flowers and seeds on your tree until about the fifth year in the ground. It is natural for wiliwili to lose all or most of their leaves during the dry summer months, and I normally do not intervene in this natural cycle; the natural rest permits the tree to eliminate any pests that may be attacking its leaves. However, if you just can’t bear to see your wiliwili without leaves, you can (sparingly) water the tree during these dry months, tricking the plant into retaining most of its leaves.

Diseases and Pests: I have already mentioned the Erythrina gall wasp. Even though we now have an ally in the fight against this pest that doesn’t mean it has disappeared. The first damage normally appears near the growing tips. If you cannot wait for the assassin wasp to show up, you can try to minimize the damage by applying systemic insecticides containing imidacloprid or acephate. Three other wiliwili pests worth noting are the Chinese rose beetle, spider mites and powdery mildew (a fungus). Rose beetles chew holes in the leaves while spider mites and powdery mildew cover the leaves with a white webbing or powder, respectively, that eventually kills the leaf. These pests make the tree unsightly but normally do not kill it. Please refer to the Enemies in the Garden page for ways to combat these pests.  

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