The United States Geological Survey lists over 30 non-native aquatic plant species colonizing water bodies in Louisiana. Some have been here for decades and remain fairly rare (such as Asian duck lettuce) while others (such as common salvinia, Salvinia minima), have covered hundreds of thousands of acres in the last 20 years. Common salvinia, along with alligator weed, water hyacinth, hydrilla, torpedo grass and water lettuce are the six most troublesome non-native species in Louisiana. Common salvinia can be controlled with herbicides but relief is temporary and repeated applications are often uneconomical. Biological control could offer a cheaper and more permanent solution.