At the tip of an iceberg: citizen science and active surveillance collaborating to broaden the known distribution of Aedes japonicus in Spain

Background: Active surveillance aimed at the early detection of invasive mosquito species is usually focused on seaports and airports as points of entry, and along road networks as dispersion paths. In a number of cases, however, the first detections of colonizing populations are made by citizens, either because the species has already moved beyond the implemented active surveillance sites or because there is no surveillance in place. This was the case of the first detection in 2018 of the Asian bush mosquito, Aedes japonicus, in Asturias (northern Spain) by the citizen science platform Mosquito Alert. Methods: The collaboration between Mosquito Alert, the Ministry of Health, local authorities and academic researchers resulted in a multi-source surveillance combining active field sampling with broader temporal and spatial citizen-sourced data, resulting in a more flexible and efficient surveillance strategy. Results: Between 2018 and 2020, the joint efforts of administrative bodies, academic teams and citizen-sourced data led to the discovery of this species in northern regions of Spain such as Cantabria and the Basque Country. This raised the estimated area of occurrence of Ae. japonicus from 7000 km2 in 2020. Conclusions: This population cluster is geographically isolated from any other population in Europe, which raises questions about its origin, path of introduction and dispersal means, while also highlighting the need to enhance surveillance systems by closely combining crowd-sourced surveillance with public health and mosquito control agencies’ efforts, from local to continental scales. This multi-actor approach for surveillance (either passive and active) shows high potential efficiency in the surveillance of other invasive mosquito species, and specifically the major vector Aedes aegypti which is already present in some parts of Europe. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).RE and FB from Mosquito Alert received funding from "la Caixa" Foundation (ID 100010434), under agreement HR18-00336 (Community-Driven Big Data Intelligence to Fight Mosquito-Borne Disease). This project has also been funded by the European Union's Horizon 2020 research and innovation program, under the grant agreement 874735 (VEO). Samplings in the Basque Country were funded by the Department of Public Health and the Department of Economic Development and Infrastructures of the Basque Government, and co-funded by the project EU-LIFE 18 IPC/ES/000001 (Urban Klima 2050)