Aedes caspius (Pallas, 1771) is a floodwater mosquito species widely distributed in the Western Palaearctic. As an anthropophilic species, its role as an arbovirus vector may be the key for understanding the transmission cycle of certain diseases in Europe such as Zika virus (ZIKV). Concerning vector competence for ZIKV, studies related to Ae. caspius are still scarce. ZIKV is an arbovirus that has provoked a widespread epidemic in the Pacific region (2007–2013) and in the Americas (2015–2016). ZIKV is associated with serious neurological injuries (e.g. microcephaly) and Guillain-Barré syndrome. Due to the ZIKV epidemics in the American continent, some viraemic travellers coming from endemic countries have been reported in Europe. More knowledge is therefore required to define the susceptibility of autochthonous mosquito species such as Ae. caspius for ZIKV in order to improve arbovirus surveillance and control programmes. In the present study, the vector competence of a European population of Ae. caspius was evaluated for two ZIKV lineages, the Suriname ZIKV strain (Asian lineage) and the MR766 ZIKV strain (African I lineage). Females were tested at 7, 14 and 21 days post-exposure (dpe) to infectious blood meals. An Ae. aegypti PAEA strain was used as a positive control. Aedes caspius presented low susceptibility to ZIKV infection and the virus was only detected by RT-qPCR in body samples. Low viral loads were detected for the MR766 strain at 7 dpe and for the Suriname strain at 14 and 21 dpe. Aedes caspius was unable to produce a disseminated infection and virus transmission at any of the tested time points. Using Ae. aegypti PAEA strain, infection, dissemination and transmission rates were calculated for the Suriname ZIKV strain (Asian lineage) at each time point. For the MR766 ZIKV strain (African I lineage), while only infection rates were estimated at each time point, no dissemination or transmission were detected in either species. The results of the present study reveal that the tested Ae. caspius population has a strong midgut escape barrier that limits the dissemination or transmission of the virus. As such, it seems unlikely that European Ae. caspius mosquitoes could be involved in ZIKV transmission if ZIKV was introduced into Europe. This information may help in designing a better strategy to European surveillance and control programmes for ZIKV.

Background: The Asian tiger mosquito, Aedes albopictus , is an aggressive invasive vector responsible for transmitting important arboviruses. Its global spread has been largely facilitated by human-mediated transport, especially through trade and road networks. Since its first detection in the Netherlands in 2005, repeated introductions have occurred via pathways such as lucky bamboo imports, used tires, aircraft, and ground traffic. Despite ongoing surveillance and elimination efforts, uncertainties remain about the origins, recurrence, and establishment potential of these introductions. Methods: We analyzed 200 Ae. albopictus specimens collected from 21 locations in the Netherlands from 2014 to 2023, including detections in residential areas and points of entry (PoEs). Samples were genotyped at 19 specific microsatellite loci. Genetic diversity and kinship were studied to better understand genetic structure, relatedness between and within locations, and local overwintering. We also determined the presence of Wolbachia endosymbiont strains in the specimens by sequencing Wolbachia markers. Results: Genetic structure and kinship analyses revealed multiple independent introductions, genetic diversity among sites, and evidence of local overwintering at both residential and PoE locations, including used tire storage sites. Close-kin relationships were identified in 63 specimen dyads. Among these, one dyad confirmed overwintering at a used tire storage facility, four indicated kinship within a residential area, and two between two locations. Genetic assignment results also highlighted successful elimination of the species in one Dutch residential area. A total of 16 Dutch locations (76.19%) tested positive for the presence of Wolbachia . Overall, 48.86% specimens analyzed tested positive for at least one strain, and 35 close-kin dyads showed complete concordance in Wolbachia infection status. Conclusions: Our findings highlight the complex invasion dynamics of Ae. albopictus in the Netherlands. Our results demonstrate that microsatellite analysis, combined with kinship assessment, is an efficient approach for investigating kinship among individuals within and between urban areas and PoEs, providing evidence of local overwintering, and assessing the genetic structure of Ae. albopictus at introduction sites. The widespread presence of Wolbachia , which is known to reduce mitochondrial diversity, suggests that mitochondrial DNA (mtDNA)-based population analyses may be limited for the species.