Recent advances in biological control of submersed aquatic weeds

The submersed aquatic plants hydrilla (Hydrilla verticillata [L.f.] Royle), Eurasian watermilfoil (Myriophyllum spicatum L.), and Brazilian egeria (Egeria densa L.) are three of the worst invasive aquatic weed problems in the U.S., with millions of dollars spent annually to control large infestations in all types of waterbodies. Historically, various control technologies have been used to manage infestations of these submersed species, including biological control. During the past five years, there has been renewed interest in biological control of submersed aquatic weeds nationally, primarily in response to the discovery in Florida of several hydrilla biotypes that have developed resistance to the herbicide fluridone. This paper summarizes the current status of biological control activities in North America during the past 10-15 years. It includes a preferred definition of biological control and describes the different approaches currently used by practitioners in the field. It also covers the types of natural enemies commonly used as biological control agents and the various abiotic, biotic, and technical factors that have contributed to project successes and failures. Finally, priority areas are identified where more resources are needed for research and outreach programs to increase the effectiveness and acceptance of biological control technology for managing submersed aquatic weeds in the future.