Ecologist Tomáš Derka. (source: Sme Archive)
In previous years, mosquito infestations in Bratislava and the Záhorie region were so severe that even top politicians took notice. The Bratislava municipality used to face annual criticism over the issue.
In early July, the municipality announced it was carrying out extensive monitoring of mosquito breeding sites near Devín Castle, covering an area of 43,000 square metres. It employed specialist equipment and the ecological biocide BTI to eliminate mosquito larvae.
This year, however, mosquitoes appear to be completely absent. In an interview with the daily Sme, ecologist TOMÁŠ DERKA from the Faculty of Natural Sciences at Comenius University explains what’s happening—and whether a mosquito outbreak could still occur.
What is the current situation? It seems there are no mosquitoes around Bratislava.
Not just seems—there really aren’t any.
Why is that?
Because of the dry conditions. Water levels in the Danube and Morava rivers have been low for quite some time. The last major flooding occurred in autumn last year. This means flood-related mosquito species have had no opportunity to reproduce, as their breeding sites have remained dry.
Have the recent rains made any difference?
No, definitely not enough. Occasionally, heavy rainfall can suffice, but more often than not, the river levels need to rise significantly and overflow. The current meteorological and hydrological conditions are simply not favourable for floodplain mosquito species, which lay their eggs in mud.
Have you been out in the field?
Yes—about a week ago, I visited the inland Danube delta. There weren’t any mosquitoes around, not even in the evening. Not a single one. It’s extraordinary.
When was the last time you recall a summer like this?
Honestly, I don’t. I’ve never experienced a mosquito-free summer before. From this perspective, it’s quite remarkable.
Is the situation the same in Záhorie?
Yes. If there are any mosquitoes, they belong to species that breed in things like water barrels. Their reproduction strategy is completely different—the female lays eggs that hatch almost immediately. Floodplain mosquitoes, by contrast, lay eggs in the mud that remain dormant until water arrives. That’s the recipe for a true infestation.
So the mosquitoes in our gardens aren’t a threat for a larger outbreak?
No. These mosquitoes don’t travel far—maybe 100 or 200 metres from where they hatch. It’s literally just neighbours swapping mosquitoes.
As usual before the summer, the Bratislava municipality announced measures against mosquitoes. Did these efforts impact the current situation?
To my knowledge, the city distributed BTI tablets to combat mosquitoes that breed in barrels. These tablets kill the larvae. As for floodplain mosquitoes, their breeding grounds need to be regularly monitored, and action taken once larvae are detected. I’m aware of one intervention, but nothing significant.
Could the situation change later in the summer?
Absolutely—and quite rapidly, within 10 to 14 days. All it takes is significant rainfall and rising water levels. Summer floods are common. For example, if there’s heavy rain in the Alps or the Morava basin, it could lead to flooding within five days—and another five to seven days later, we could be facing a mosquito outbreak.
So we can’t say for certain that the summer will be mosquito-free?
No. After all, it’s only mid-July. If an intervention is needed in summer, it must be carried out very quickly—within two or three days—otherwise it could be too late. Mosquitoes develop rapidly in warm water. Last year there was a significant flood in September, and mosquitoes were still present. But since it was already autumn, the days were shorter, nights cooler, and people were wearing more clothes—so it wasn’t as problematic as a midsummer infestation.
As an expert, what does a summer without mosquitoes mean to you?
Like everyone else, I find it far more pleasant. I don’t miss them at all—I’m delighted to be able to spend time in the garden in the evening. But when mosquitoes are around, it’s fine too. They’re part of nature, and I adapt.
I meant more in terms of your work—are you bored now?
Not at all. I also deal with other groups of aquatic insects. I live in Vysoká pri Morave (a village in Záhorie – Ed. note) and I have a bit of a reputation as a “mosquito protector”. In fact, I’ve probably killed more mosquitoes than anyone else in the village. I go around distributing BTI, wiping out millions. I’m not a protector of mosquitoes—I protect everything that would be harmed by non-selective insecticides. BTI only targets mosquito larvae.
©Sme
