Sources and sewers influence the presence of mosquitoes in cities

A study carried out by the Doñana Biological Station (EBD-CSIC), together with the University of Granada (UGR), the Biomedical Research Center in Epidemiology and Public Health Network and the Barcelona Public Health Agency (ASPB) has revealed how the environmental characteristics and the structure of the sewage systems and of the sources ornamentals influence the presence of native and invasive mosquitoeslike the tiger mosquito.

The research, which was based on data collected between 2015 and 2019 in the city of Barcelonahighlights that the fountains without water recirculation systemmoderate temperatures and the accumulation of water in the sewer system are related to an increase in mosquito populations in urban areas.

The researchers studied the presence of larvae of three species of mosquitoes in water infrastructuressuch as sewers and ornamental fountains, from the ten districts of Barcelona.

The species studied were Asian tiger mosquito (Aedes albopictus), the common mosquito (Culex pipiens) and the species longiareolata culiseta.

During the study period, more than 230,000 visits were made to 31,000 scuppers (sanitation elements that transfer runoff water to the sewage system) and more than 1,800 inspections of 152 ornamental fountains in Barcelona.

The results determined that the mosquitoes used most often the sand scuppers (those that accumulate more water).

Furthermore, it was also confirmed that an increase in minimum temperatures and rainfall are associated with a greater presence of mosquitoes in the city, while both very high temperatures and very abundant rains contribute to reducing their proliferation.

In the case of the sources, it was observed that mosquitoes colonized above all those that They do not have systems for the recirculation of water and that they have vegetation around them.

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Currently, the ASPB has started a program that modifies the structure of the sand scuppers to prevent the accumulation of water and thus prevent mosquitoes from using them to reproduce. It has also verified that the use of larvicidal treatments can be effective in reducing the presence of larvae in those spaces.

Specifically, the bti is a biological larvicide that acts selectively on these, offering a safe alternative and respectful with the environment.

These treatments have shown a significant decrease in the presence of mosquitoes in the treated scuppers. However, these are measures that must be repeated periodically, since mosquitoes reappear 10 to 25 days after the application of the larvicide.

The study’s senior author, Thomas Montalvo, points out that “mosquito surveillance and control programs require this type of evaluation that allows the evidence to be valued to improve the management and health of people through a strategy OneHealth» (which considers that there is only one health that combines the human, animal and environmental dimensions).

This finding highlights the need to adequately monitor and schedule larvicidal treatments to achieve effective and sustainable control of these insects, by identifying the infrastructures with the highest risk of colonization.

The main author of the study and researcher at the EBD-CSIC Martina Ferraguti affirms, for her part, that “these results provide valuable information to understand how the structure of our cities influences the presence of mosquitoes and how with small actions we can reduce their populations. By better understanding the factors and processes that affect them in urban areas, “we can work on developing effective strategies to control populations and reduce risk to public health,” he adds.

In addition, this study highlights the importance of close collaboration between the scientific community, public health authorities and citizens to address these types of problems in cities.