UC Riverside

The arroyo chub, Gila orcutti, is native to the watersheds of southern California and has been proposed as a replacement for the non-native western mosquitofish, Gambusia affinis, as a biological control agent for mosquitoes in sensitive watersheds throughout the region. Because mosquito-eating fish are not strictly larvivorous, they also have the potential to impact non-target organisms in systems where they are introduced. The impact of arroyo chub stocking density on the invertebrate community, and the suitability of a riverine constructed wetland as conservation habitat for the arroyo chub population, in the Santa Ana River were evaluated at the Prado Wetlands in Riverside County, California. Invertebrate abundance and community structure did not differ significantly among three stocking densities (0, 1.5 and 6 kg/ha) during a five-week study in cage mesocosms. Approximately 16 months after stocking G. orcutti into a 0.9-ha wetland, nearly 3,700 fish were collected; however, no arroyo chubs were recovered. All of the fish collected were invasive species in the Santa Ana River system and piscivory by non-native species most likely caused the extirpation of the arroyo chubs in the wetland.

The ovipositional responses of female Culex tarsalis to semiochemicals produced by aquatic organisms in three aquatic guilds (predaceous insects, algivorous fish and predatory/larvivorous fish) were examined in laboratory choice assays. Previous binary choice trials have shown that female mosquitoes avoid laying eggs on water that contains fish exudates and will instead choose to oviposit on water without kairomones released by fish. Culex tarsalis was not deterred from ovipositing in cups containing semiochemicals from invertebrate predators and algivorous fish, but was deterred from ovipositing in cups containing arroyo chub semiochemicals.