U.S. Army Corps of Engineers scientists and researchers from the U.S. Department of Agriculture (USDA) began overseas research in the late 1960s to find biological control agents for use in aquatic plant management. This search for natural plant enemies (insects and fungal pathogens) has led researchers to the native ranges of noxious aquatic plants, located throughout the continents of Africa, Asia, Europe, and Australia. For Corps aquatic plant managers, the two most troublesome aquatic plants are the exotic species Eurasian watermilfoil (Mydophyllum spice turn) and hydrilla (Hyddlla verticfflata). These species, which account for more that two thirds of all noxious aquatic weed acreage in the United States, have similar characteristics. They are rooted submersed macrophytes that grow to the water's surface, forming extensive mats of vegetation that restrict navigation and recreational use of waterways. Records document the establishment of milfoil in the United States by 1881 (Balciunas 1982) and hydrilla, by the late 1950s or early 1960s (Balciunas 1985).