Heat and regular rain, this has been the year with the most mosquitoes in Spain

2020 has been a year marked by the COVID-19 pandemic and an unusual year in terms of number of tiger mosquitoes. Twice as many of these insects have been observed as last year, accumulating 1,798 notifications compared to 885 in 2019. The year of the pandemic has turned out to be the year with the most tiger mosquitoes recorded by the Mosquito Alert project since 2014.

“Tiger mosquito densities are always explained by two factors, climate and human behavior, both of which are the ones that periodically provide them with water points, where they breed,” explains Frederic Bartumeus, co-director of the project and researcher in ICREA in the CEAB-CSIC and CREAF.

The 2020 mosquito season kicked off with a warm, rainy spring that encouraged them to proliferate during the months of May and June. In addition, according to Roger Eritja, entomologist of CREAF and the project, confinement could have played a relevant role in these data “the ban on traveling to second homes during the months of March and April could affect the maintenance of its gardens, swimming pools and terraces, where it was possible to accumulate the water that mosquitoes need to multiply “, he comments.

Tropical summer

This explosion of mosquitoes in the spring was followed by a summer that, for the sixth consecutive year, recorded higher-than-normal temperatures, with intense and repeated episodes of rainfall on the peninsula. The Mediterranean sea is warming, summer is advancing, prolonging and more intense, conditions that can benefit the tiger mosquito by being accompanied by regular rains as has happened this year.

These climatic conditions have two effects on mosquitoes. In summer, high temperatures allow the larvae to develop faster, shortening the time between generations, and leading to exponential growth of their populations, as long as they have places with water to breed. On the other hand, global warming, with a warm spring and fall, could extend its seasonality by allowing mosquitoes to be active for more days of the year.

Fig 1. Photograph of tiger mosquito and some larvae. Source: Mosquito Alert CC-BY

Mushrooms, chestnuts and mosquitoes

Autumn is warming and mosquitoes remain active, as evidenced by the more than 250 reports the Mosquito Alert platform has received in the past two weeks, and more than 250 confirmed observations of tiger mosquitoes between October and November. In 2019, in the same period, 116 tiger mosquitoes were reported, 9 of them in November, until November 28, 2020 50 reports of tiger mosquitoes have been recorded, this is five times more than the year previous. Beyond temperatures, what most affects the abundance of mosquitoes is to have availability to reproduce, that is, to have water in the breeding sites, either due to the presence of regular rain or activity. human.

“Having modeled the data, considering the number of users with the application by region and their degree of participation, we see that 2020 slightly exceeds 2015 although its patterns have been very different,” says John Palmer, professor of the UPF and codirector of the project.

This year’s weather conditions have been favorable to the mosquito continuously since spring, while in 2015 its populations exploded exponentially in the summer. Understanding the climatic and social factors that determine the dynamics of their populations will allow them to predict their abundance in the future.