Quassia, also known as bitter ash, bitter wood and amargo, is a small flowering tropical tree original to the West Indies, although it is also grown commercially in other parts of the world. The plant is reputedly named in honor of Quassi of Surinam, the 18th century Surinamese botanist who first discovered the fever reducing properties of the bark. The bark is also a traditional ingredient in herbal bitters and digestifs.
The compounds in quassia bark make this herb an effective natural insecticide. In fact, it’s a common ingredient many commercial insecticide products and is approved for use in Switzerland for organic farming. Quassia is also used to control mosquito larvae in ponds without causing harm to fish.