Gregarine parasites are adapted to mosquito winter diapause

Abstract

The Asian tiger mosquito Aedes albopictus is one of the most invasive species of mosquito. The prevalence of its apicomplexan gregarine parasite Ascogregarina taiwanensis is high in natural populations across both temperate and tropical regions. However, the parasite's oocysts cannot colonize the insect host during winter, when the mosquito lays diapausing eggs. It is therefore unclear if the parasite can survive outside of its insect host during the cold season in temperate regions. Oocysts stored for 1 month at a low temperature (representative of the temperatures that occur during periods of mosquito diapause) were as infectious as fresh oocysts, but those stored for the same period of time at a higher temperature (representative of the temperatures that occur during periods of mosquito activity) were uninfectious. We therefore suggest that the parasite has evolved traits that maximize its maintenance during periods of mosquito dormancy, while traits that would enable its long term survival during periods of mosquito activity have not been selected for.

Keywords: Aedes albopictus; Apicomplexa; Ascogregarina; Thermal tolerance.

Fig. 1

Number of oocysts per adult mosquito across the experimental conditions. Females (blue) and males (yellow) were tested across three independent replicate batches. The violin plots show the log₁₀ of total oocyst number + 1 across the experimental conditions. In the Fresh oocysts treatment, infected mosquitoes were crushed into sterile water which was immediately used to seed the water in the tray containing the unparasitized 1st instar larvae. Non-infected mosquitoes were unparasitized and used as a control to confirm that no residual parasites had colonized the test population. In the Parasite kept 1 month at 26 °C or 4 °C treatments, infected mosquitoes were crushed in sterile water and stored for 1 month at 26 °C or at 4 °C, respectively before being seeded to tray containing unparasitized 1st instar larvae. Larvae were reared to adult mosquitoes before parasitism measurement