2012 Annual Report 1a.Objectives (from AD-416): Evaluate efficacy, applicability and utility of Hydrellia spp as a biological control agent for management of Egeria densa. 1b.Approach (from AD-416): Efficacy and host specificity will be determined using standard, accepted methods for assessing feeding (with and without alternative host plants) and reproductive behavior both in the country of origin (Argentina) and under certified quarantine glasshouse and growth chamber conditions at Albany, California. Range of water depths of feeding impacts will be determined using field sampling and multi-depth culture systems in Argentina. Developmental timing and temperature required for growth, reproduction and dispersal will be assessed to compare with conditions in proposed release site (Sacramento-San Joaquin Delta). 3.Progress Report: Research was completed on a cooperative program between ARS scientists in Albany and Davis, California, and ARS scientists in Buenos Aires, Argentina, on the assessment of insect natural enemies of Egeria densa, Brazilian waterweed. This work relates to Objective 3 of the parent project, Biological Control of aquatic weeds, and was supported by the California Department of Boating and Waterways. This effort was conducted to investigate the potential of foreign natural enemies to control this invasive aquatic weed in areas of the Sacramento/ San Joaquin River Delta. This research started in 2009 when foreign exploration activities were implemented in Brazil and Argentina where Egeria densa is a native species. In South America, this plant grows primarily in the Parana River Basin. Extensive surveys were conducted over a wide range of latitudes and many potential herbivorous insects were collected and evaluated to assess their potential as introduced biological control agents for North American release. To date, only a single insect, a leafmining fly, Hydrellia spp., which is a new species to science has been selected for further evaluation. This insect feeds on Egeria densa and causes extensive damage in its native range. It was tested extensively at the ARS laboratory in Buenos Aires and determined to be relatively host specific and efficacious to Brazilian waterweed. ARS scientists are currently in the process of importing this insect into the USDA quarantine facility in Albany, CA, where further testing will support the development of a regulatory petition requesting its release into California. Additional host specificity and safety testing are planned and will be used to provide data for Federal and State permits to continue this research.