Distribution, Abundance and Field Host‐Range of Hydrellia balciunasi Bock (Diptera: Ephydridae) a Biological Control Agent for the Aquatic Weed Hydrilla verticillata (L.f.) Royle

During a project to detect and evaluate potential biological control agents for the submersed aquatic weed, hydrilla (Hydrilla verticillata), the distribution, abundance and field host‐range of a recently described aquatic fly, Hydrellia balciunasi were studied in Australia from 1985‐1992. A total of 17,729 specimens were collected at 55 sites in Queensland, New South Wales and the Northern Territory. H. balciunasi was found to be relatively common, being collected in 57% of 550 collections of hydrilla. Although larvae were collected from 17 aquatic plant species, hydrilla was the preferred host for this fly, with 97% of the specimens collected from it. Based on these field data, H. balciunasi was exported to quarantine in the United States of America in 1988 for laboratory evaluation of its host‐range. Quarantine studies confirmed its safety as a biological control agent, allowing its release in the field in Florida in 1989. This is the first endemic Australian insect released as a biological control agent for a weed in the U.S.A.