Population Dynamics, Resource Use, and Conservation Needs of the Delhi Sands Flower-loving Fly (Rhaphiomidas Terminatus Abdominalis Cazier) (Diptera: Mydidae), an Endangered Species

The Delhi Sands Flower-loving Fly (Rhaphiomidas terminatus abdominalis Cazier), the only Dipteran listed as endangered in the United States, is a large, nectar-feeding pollinator fly, found only in remnants of a sand dune ecosystem in southern California. A five-year observational study was conducted in a 3.7ha preserve. Legal and biological constraints limit accuracy of population data because marking individuals was not possible. The population on the preserve appeared to be stable over the period of observation. Little variation in number of flies observed from year to year was found. Spatial distribution of fly observations differed for each fly generation, but reasons for this are not clear. Distribution of male and female flies differed from each other most of the time. Understanding aspects of the fly's ecology and behavior and the ecosystem dynamics is necessary to effectively plan for conservation and recovery of the species. Preserves must provide all of the elements needed for continued survival of the species through maintenance of its dynamic habitat.