Scientists blame climate change for unexpected mosquito activity in Portugal

The tendency in recent years has been for more unexpected phenomena to start to appear: mosquito activity is becoming more erratic, with more activity reported in the out-of-season period when mosquito numbers should diminish.

There are no new species in Portugal, nor has there been a change in the behaviour of mosquitoes. The explanation, experts say, may be climate change, which causes a larger quantity of usual mosquitoes than usual. “Climate change, which results in colder nights, or two or three days of very hot weather followed by rapid cooling, causes mosquitoes to spring in to action or hatch more eggs in tune with this change, so there are more mosquitoes in a shorter period of time.”, explains Maria João Alves, a researcher at the Dr. Ricardo Jorge National Institute of Health.

The species that vex Portugal “are the same species that we have always had”, but it is possible that “there is a larger quantity of mosquitoes” in Portugal that need to have quick “blood meals” to sustain themselves. In addition, “in summer people are more exposed and more out at night, so there may be more bites – but there is nothing described that there are variations in behaviour or new species.”

Does this mean that in the future we will have more and more mosquitoes? Not necessarily, says the coordinator of the National Vector Surveillance Network. What should happen, they explained, is that we will see more and more unexpected phenomena on both ends of the spectrum: more out-of-season mosquitoes some years, and less out-of-season mosquitoes in other years.

“Climate change will do more to surprise us in this regard: more will hatch in months we aren’t expecting much activity, and fewer mosquitoes could hatch in times when we are typically used to it.” In Portugal, mosquito activity occurs mainly between May and October. However, environmental changes have caused variations. A few years ago, the researcher recalls an example when there was strong activity in November, after a period of rainy weeks, followed by heat and rain again. “The rain created aquatic environments which were perfect breeding places for mosquitoes, which caused them to hatch more in November,” explains Maria João Alves.

At the pest management summit that took place last year in Cascais, Brazilian entomologist Roberto Pereira of the University of Florida warned of this phenomenon: in cities, there are already more mosquitoes and flies throughout the year as opposed to focused more in certain periods of the year, which transmit epidemic diseases to humans.

He explained that these will “get along” with the increase in environmental temperature. In the insect life cycle, where a single generation takes a few weeks, many more insect generations can easily follow, he warned.

Globalization, as well as increased travel and international trade, may also alter the geographical boundaries of some species as well and, consequently, vector-borne diseases and news species could more easily spread. For now, says Maria João Alves, “there is no cause for alarm, as the National Vector Surveillance Network has not identified any viral activity.”