sentences:  As chemical and mechanical removal is often too expensive, polluting, and ineffective, researchers have turned to biological control agents to deal with water hyacinth.The effort began in the 1970s when USDA researchers released into the United States three species of weevil known to feed on water hyacinth, "Neochetina bruchi", "N. eichhorniae", and the water hyacinth borer "Sameodes albiguttalis".The weevil species were introduced into the Gulf Coast states, such as Louisiana, Texas, and Florida, where thousands of acres were infested by water hyacinth.