Ascogregarina taiwanensis infection in Aedes aegypti and Aedes albopictus in Santa Catarina, South Brazil

Presence of Ascogregarina culicis and Ascogregarina sp. in natural sympatric populations of Aedes aegypti and Ae. albopictus (Diptera: Culicidae) in Argentina

Aedes aegypti is the main vector of the four arboviruses in America which have the greatest impact on human health. The introduction of Aedes albopictus in South America and Argentina acquires importance given the possibility that this species may be a new vector of arboviruses in this region. For this reason, the studies of the biology of their parasites, such as Ascogregarina spp., should be important for the knowledge of the invasive behavior of these vectors. We reported the finding of Ascogregarina culicis in Aedes aegypti and Ascogregarina sp. in Ae. albopictus populations in subtropical Argentina. The prevalence of parasitism by A. culicis in Ae. aegypti and Ascogregrarina sp. in Ae. albopictus was 34.81% (n = 464) and 37.23% (n = 70), respectively, differing between the seasons and habitats. The infection intensity caused by A. culicis and Ascogregarina sp. varied between 1 to 250 and 1 to 327 trophozoites respectively. Ascogregarina culicis was found throughout the all sampling period of Ae. aegypti (June 2016-April 2018). However the presence of Ascogregarina sp. in the midgut of Ae. albopictus was not recorded throughout the whole sampling period despite the presence of the host.

Parasitism of Aedes albopictus by Ascogregarina taiwanensis lowers its competitive ability against Aedes triseriatus

Background

Mosquitoes are vectors for diseases such as dengue, malaria and La Crosse virus that significantly impact the human population. When multiple mosquito species are present, the competition between species may alter population dynamics as well as disease spread. Two mosquito species, Aedes albopictus and Aedes triseriatus, both inhabit areas where La Crosse virus is found. Infection of Aedes albopictus by the parasite Ascogregarina taiwanensis and Aedes triseriatus by the parasite Ascogregarina barretti can decrease a mosquito’s fitness, respectively. In particular, the decrease in fitness of Aedes albopictus occurs through the impact of Ascogregarina taiwanensis on female fecundity, larval development rate, and larval mortality and may impact its initial competitive advantage over Aedes triseriatus during invasion.

Methods

We examine the effects of parasitism of gregarine parasites on Aedes albopictus and triseriatus population dynamics and competition with a focus on when Aedes albopictus is new to an area. We build a compartmental model including competition between Aedes albopictus and triseriatus while under parasitism of the gregarine parasites. Using parameters based on the literature, we simulate the dynamics and analyze the equilibrium population proportion of the two species. We consider the presence of both parasites and potential dilution effects.

Results

We show that increased levels of parasitism in Aedes albopictus will decrease the initial competitive advantage of the species over Aedes triseriatus and increase the survivorship of Aedes triseriatus. We find Aedes albopictus is better able to invade when there is more extreme parasitism of Aedes triseriatus. Furthermore, although the transient dynamics differ, dilution of the parasite density through uptake by both species does not alter the equilibrium population sizes of either species.

Conclusions

Mosquito population dynamics are affected by many factors, such as abiotic factors (e.g. temperature and humidity) and competition between mosquito species. This is especially true when multiple mosquito species are vying to live in the same area. Knowledge of how population dynamics are affected by gregarine parasites among competing species can inform future mosquito control efforts and help prevent the spread of vector-borne disease.