Aedes albopictus larvae collected in Gainesville, FL, were infected with the gregarine Ascogregarina taiwanensis. Natural prevalence varied from 68 to 100%. Eight mosquito species were tested in the laboratory for susceptibility to A. taiwanensis isolated from field-collected Ae. albopictus. Aedes aegypti, Aedes albopictus, and Aedes taeniorhynchus became 100% infected in the larval stage, whereas Aedes triseriatus was less susceptible; Culex quinquefasciatus, Culex nigripalpus, Culex territans, and Anopheles quadrimaculatus were not susceptible. Viable A. taiwanensis oocysts from adults were recovered from Ae. taeniorhynchus (30%) and Ae. albopictus (100%); no oocysts were produced in the other exposed hosts. Mortality induced by A. taiwanensis infection was low in all mosquitoes except Ae. taeniorhynchus. We conclude that A. taiwanensis has little short-term impact on the mortality of the 3 most common container-inhabiting mosquito species in Florida; however, the long-term impact on overall host population regulation has yet to be determined.