Koa and Koa Bug

  The koa (Acacia koa) is the largest tree in the Hawaiian forest. Koa in Hawaiian also means fearless and warrior. The Hawaiian phrase E ola koa! “Live like the koa!” Means to live long like the koa tree.

The tallest koa with large straight trunks grow in the mountain forests above 2,000 feet (650 m). They can live for 80 to 150 years, growing to be 155 feet (33 m) tall. The islands of Maui and Hawai‘i have the tallest mountains, and also the largest koa. Hawaiians used giant koa trunks to make large voyaging vessels called wa‘a. These wa‘a were between 60–100 feet (20–33 m) long.

At lower elevations, koa grows as more of a small tree or large shrub, with many branches instead of a single trunk. A lower elevation koa usually only lives for less than 20 years.

The hard and heavy koa wood is prized for all types of woodworking. Koa is a tone wood, which makes especially beautiful sounding instruments like ukulele, and guitars.

Koa has many special characteristics that make it a strong and fast growing tree. The koa has symbiotic bacteria in its roots that takes nitrogen from the air and gives it to the koa. With the help of the nitrogen-fixing bacteria, a young tree can grow to 25 feet or (8 m) in 5 years.

The distinctive long sickle shaped “leaves” of the koa are actually flattened leaf stems, called phyllodes. The tough phyllodes stand up to the harsh tropical sun. The true leaves are tiny leaves that grow from stems at the ends of the phyllodes. The small true leaves resemble the leaves of the koa haole, or false koa (Leucaena leucocehala). The more delicate true leaves collect sunlight in shadier conditions.

 The koa is home to many animals. Birds use the tall trees for nesting and food. Insects like the koa bug (Coleotichus blackburniae) depend on the koa too. The koa bug is a endemic small jewel-like stink bug. The koa bug has lost its defensive stinky spray. It feeds on sap from the koa seed pods. Habitat loss, and introduced predators and parasites have reduced koa bug populations.

The koa bug is similar to the invasive southern green stink bug that was damaging agricultural crops. In 1966, parasitic flies were introduced to control the southern green stink bug populations. The flies also targeted the endemic koa bugs. This was an early lesson to be more careful when introducing biological control agents (BCAs). Scientists and regulators have made progress in preventing subsequent biological control agents affecting non-target organisms.