Human-aided dispersal and population bottlenecks facilitate parasitism escape in the most invasive mosquito species.

During biological invasion process, species encounter new environments and partially escape some ecological constraints they faced in their native range, while they face new ones. The Asian tiger mosquito Aedes albopictus is one of the most iconic invasive species introduced in every inhabited continent due to international trade. It has also been shown to be infected by a prevalent yet disregarded microbial entomoparasite Ascogregarina taiwanensis. In this study, we aimed at deciphering the factors that shape the global dynamics of A. taiwanensis infection in natural A. albopictus populations. We showed that A. albopictus populations are highly colonized by several parasite genotypes but recently introduced ones are escaping it. We further performed experiments based on the invasion process to explain such pattern. To that end, we hypothesized that (i) mosquito passive dispersal (i.e. human-aided egg transportation) may affect the parasite infectiveness, (ii) founder effects (i.e. population establishment by a small number of mosquitoes) may influence the parasite dynamics, and (iii) unparasitized mosquitoes are more prompt to found new populations through active flight dispersal. The two first hypotheses were supported as we showed that parasite infection decreases over time when dry eggs are stored and that experimental increase in mosquitoes' density improves the parasite horizontal transmission to larvae. Surprisingly, parasitized mosquitoes tend to be more active than their unparasitized relatives. Finally, this study highlights the importance of global trade as a driver of biological invasion of the most invasive arthropod vector species.

Crosstalk between the microbiota and insect postembryonic development.

Insect sequential development evolves from a simple molt towards complete metamorphosis. Like any multicellular host, insects interact with a complex microbiota. In this review, factors driving the microbiota dynamics were pointed out along their development. Special focus was put on tissue renewal, shift in insect ecology, and microbial interactions. Conversely, how the microbiota modulates its host development through nutrient acquisition, hormonal control, and cellular or tissue differentiation was exemplified. Such modifications might have long-term carry-over effects on insect physiology. Finally, remarkable microbe-driven control of insect behaviors along their life cycle was highlighted. Increasing knowledge of those interactions might offer new insights on how insects respond to their environment as well as perspectives on pest- or vector-control strategies.

Gregarine parasites are adapted to mosquito winter diapause.

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.

Microorganisms Associated with Mosquito Oviposition Sites: Implications for Habitat Selection and Insect Life Histories.

Mosquitoes are considered one of the most important threats worldwide due to their ability to vector pathogens. They are responsible for the transmission of major pathogens such as malaria, dengue, zika, or chikungunya. Due to the lack of treatments or prophylaxis against many of the transmitted pathogens and an increasing prevalence of mosquito resistance to insecticides and drugs available, alternative strategies are now being explored. Some of these involve the use of microorganisms as promising agent to limit the fitness of mosquitoes, attract or repel them, and decrease the replication and transmission of pathogenic agents. In recent years, the importance of microorganisms colonizing the habitat of mosquitoes has particularly been investigated since they appeared to play major roles in their development and diseases transmission. In this issue, we will synthesize researches investigating how microorganisms present within water habitats may influence breeding site selection and oviposition strategies of gravid mosquito females. We will also highlight the impact of such microbes on the fate of females' progeny during their immature stages with a specific focus on egg hatching, development rate, and larvae or pupae survival.