Wasps Invade Native Trees
Maui, Hawaii

In 2003, the leaves and stems of trees of the Erythrina genus in Taiwan were found mysteriously swollen. The culprit was identified as a never-before-seen species of wasp, which lays eggs in the trees, deforming them with galls. The wasp has since appeared across the tropics where Erythrina trees grow.

By 2005, the Erythrina gall wasp spread to most of the Hawaiian Islands. Scientists suspect infested leaves found their way into a Hawaii-bound boat shipment from Taiwan, and in a similar fashion hopped from island to island on Hawaii.

On Maui, scientists first noticed infestations on nonnative, ornamental Erythrina variegata trees near Kahului Harbor. The wasp has since spread south to the native Erythrina sandwicensis forest. These trees, locally called wiliwili, flourish on the dry leeward slopes of the Haleakala volcano. Wiliwili are not only a keystone species in this ecosystem but have been long valued by Hawaiian communities for their flowers, seeds, and wood.

Scientists are currently testing insecticide controls and are investigating biological agents in Africa to help stop the wasp from destroying Hawaii’s treasured native forest.

Image Credits 
The World and Hawaii, May 2004 (Blue Marble Next Generation: satellite: NASA Terra, sensor: MODIS)
Maui (satellite: NASA Landsat 7, sensor: ETM+)
Wasp (Mark Schmaedick)
Wiliwili (courtesy Art Medeiros)
Galls (HEAR)
Wasps in galls (Michelle N. Tremblay)

Related Science Bulletins 
Stalking an Alien Seaweed (October 31, 2005)
Scanning Invasive Species (March 28, 2005)