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

Abstract

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.

A mosquito densovirus infecting Aedes aegypti and Aedes albopictus from Thailand.

“…[20][21][22] It has been proposed that a Gregarine parasite may be mediating competition between the two mosquito species in North America. [23][24][25] However, similar observations have not been reported in Thailand, where Ae. aegypti numbers have remained high even in areas where the two species share larval habitats.…”

Aedes aegypti and Aedes albopictus in Bermuda: extinction, invasion, invasion and extinction

“…Several additional considerations could be made; one possibility is that A. albopictus introduced diseases to the islands that compromise A. aegypti populations (such as Ascogregarina, e.g., Blackmore et al 1995), causing a reduction in their rate of growth. Juliano (1998) found no evidence to support this idea in his Florida competition study, but he did not manipulate the presence or absence of parasites to examine relative susceptibilities, and did not examine dead larvae from his competition experiment, in which some treatment combinations resulted in total larval mortality.…”

“…The potential for parasite alteration of a competitive interaction has been shown by Aliabadi and Juliano (2002), who showed a reduced dominance by A. albopictus when competing with native A. triseriatus. The degree of host specificity and pathogenicity by the two species of Ascogregarina involved remains uncertain; some studies indicate that cross-infection between these two mosquitoes and their natural parasites can occur with deleterious effects (Munstermann and Wesson 1990), and others do not (Blackmore et al 1995 found higher prevalence of Ascogregarina spp. among A. aegypti in areas that had not yet been invaded by A. albopictus), but the Ascogregarina-Aedes interactions have still not been thoroughly studied and a number of other parasites, including fungi, flagellates and bacteria could also play a role (Fukuda 1992).…”

A field test for competitive effects of Aedes albopictus on A. aegypti in South Florida: differences between sites of coexistence and exclusion?

“…Predators like T. rutilus and C. appendiculata seem to be relatively rare in cemetery vases, tires, and more urban containers in south Florida (Frank 1981;O'Meara et al 1995;personal observation), but there has been relatively little systematic investigation of the question of the potential effects of predators in modifying interspecific competition in these habitats. Although there has been considerable interest in the impact of parasitic protozoa in the genus Ascogregarina on the competitive interaction of A. albopictus and A. aegypti (e.g., Blackmore et al 1995) both observational (Garcia et al 1994) and experimental (Juliano 1998) evidence suggests that Ascogregarina play, at best, a secondary role in determining the outcome of this invasion.…”