Surveillance And Control Of Mosquitoes In Sewers From An Urban Mediterranean Area

Urban areas provide suitable breeding areas for mosquitoes potentially affecting the epidemiology of many vector-borne diseases, through its effects on mosquito community composition. The invasive Asian tiger mosquito Aedes albopictus has colonized a large number of urbanized areas in Europe and is still increasing its distribution range. This species uses small water depots for laying their eggs and larval development, and anthropogenic areas offer multitude of potential breeding sites. Nowadays, most control programs of Ae. albopictus populations are based on the use of Bacillus thuringensis (BTI) although its efficacy under natural conditions have been traditionally neglected. As a part of an extensive study, we monitored the presence of
larvae of mosquitoes including the invasive Ae. albopictus and the native Culex pipiens and Culiseta  longiareolata in 73 neighbourhoods and 10 districts of the city of Barcelona from February to December during five consecutive years (2015-2019). Overall, more than 73000 sewers were inspected, which can be accessible breeding larval sites, in order to identify the annual and seasonal variation on the colonization process of sewers and the effects of water infrastructure characteristics. We found clear interannual differences in the presence of mosquito larvae in the area, reaching the maximum numbers during 2015 and 2018. In addition, the presence of mosquito larvae increased along the year, with the highest percentages of larvae in water infrastructures during August. Furthermore, our results highlight clear differences in the presence of mosquito larvae according to the typology of the sewers, being the sand sewers the one with the highest percentage of mosquito breeding activity. These results support that the typology of water infrastructures affects the presence of mosquito larvae, including those of the species Ae. albopictus, in a
Mediterranean urban area and provide important information on the seasonality of mosquito reproduction useful for monitoring and surveillance programs of mosquitoes in the public sewage system.