Invasive species in Hawaii and health-related problems. The introduction of mosquitoes to Hawaii has resulted in the spread of avian malaria, and increases the risk of dengue and west Nile virus (not known to be in Hawaii yet). Other native species can be affected by invasive species diseases as well, such as the once-dominant koa tree being killed by koa wilt, which is believed to have been brought into Hawaii on an ornamental acacia plant, and the 'ohi'a tree, now being affected by Rapid Ohia Death. Invasive predators can severely reduce the population sizes of native species, or even drive them extinct, because native
Acacia koa arranged end-to-end in the pod, rather than side-by-side. The phyllodes are also usually straighter, though this character is variable in both species. The wood is denser, harder, and more finely grained than koa wood. Koaia has been much more heavily impacted by cattle and is now rare, but can be seen on ranch land in North Kohala. The koa population has suffered from grazing and logging. Many wet forest areas, where the largest koa grow, have been logged out, and it now comes largely from dead or dying trees or farms on private lands. Although formerly used for outrigger canoes,