Parasitism of Aedes aegypti and Ae. albopictus (Diptera: Culicidae) by Ascogregarina spp. (Apicomplexa: Lecudinidae) in Florida.

Aedes aegypti (L.) and Ae. albopictus (Skuse) from 40 sites in 17 counties of Florida were surveyed for gregarine parasites during the spring and autumn of 1993 and in July 1994. Larvae collected from containers (mainly tires) were dissected to determine the number of gregarine trophozoites present. Ascogregarina spp. were found at 70% of the sites and occurred as frequently in Ae. aegypti populations as in Ae. albopictus. Within sites, parasite distributions were highly variable and aggregated in host populations. Parasite loads ranged from 1 to 486 trophozoites per host. Mean parasite load was significantly higher in Ae. aegypti larvae (52.5 per host) than in Ae. albopictus (33.5 per host). Parasite prevalence was significantly higher in Ae. aegypti populations that were not sympatric with Ae. albopictus compared with allopatric Ae. albopictus or sympatric populations of either species. In sympatric populations, Ae. aegypti tended to have equal or higher parasite prevalence than the cohabiting Ae. albopictus. Ascogregarina taiwanensis (Lien & Levine) prevalence in Ae. albopictus was significantly higher in areas where these hosts have been present for at least 3 yr. These data contribute to the hypothesis that parasite-mediated competition may be a factor in the apparent displacement of Ae. aegypti by Ae. albopictus in Florida.