Abstract
Monoecious and dioecious forms of the submerged aquatic plant hydrilla, Hydrilla verticillata (Hydrocharitaceae) are invasive weeds in the United States. Monoecious hydrilla is expanding northward and the existing biological control agents are not controlling it effectively. Results of fine-scale genetic identification of plants and herbivores matched the invasive US monoecious hydrilla genotype with a leaf-mining fly, Hydrellia sp. in their native range in the Republic of Korea. This fly was imported into quarantine in Australia to conduct preliminary evaluations of its biology, life-history and host range; a pre-screening before considering its importation into US quarantine for complete assessment as a potential biological control agent. The fly completed its development on two non-target test plant species, Elodea canadensis and Potamogeton crispus, the former being native to North America. It was recommended that no further consideration be given to Hydrellia sp. as a biological control agent of monoecious hydrilla. Other Hydrellia species from the Republic of Korea and China found on monoecious hydrilla should instead be evaluated.