Basel’s tiger mosquitoes may be disappearing as temperatures drop, but their eggs can survive the winter. After a season of particularly high mosquito numbers, what does this mean for next spring? Pie Müller, medical entomologist and Head of Vector Biology at Swiss TPH, explains the challenges of controlling tiger mosquitoes and how research, surveillance and coordinated prevention can help Basel tackle the problem.
“As days shorten in autumn, female tiger mosquitoes lay eggs that remain dormant through winter and hatch the following spring. Given the high mosquito numbers in Basel this year, we expect many of these eggs to survive until next spring. This makes an early start to prevention especially important.
The Asian tiger mosquito is spreading across Europe, and Basel is no exception. Rising temperatures help it thrive, while urban environments offer plenty of places to breed. Even a small volume of standing water in plant saucers, gutters or buckets can provide suitable breeding habitats. Catch basins can be particularly important breeding sites because they may retain water even during prolonged dry periods, as observed in Basel this summer.
At Swiss TPH, we have been studying the species since 2011. Our monitoring on behalf of the federal government and cantons, including Basel-Stadt, helps authorities decide where to focus prevention and control and check whether their measures are working.
Our research also shows how to optimise the effectiveness of control measures. In Basel, we investigated how frequently catch basins need treatment with VectoMax FG, a product containing naturally occurring bacterial toxins that kill mosquito larvae. Our results showed that treating catch basins every four weeks reduced the number of emerging tiger mosquitoes by at least 90%, whereas mosquito numbers began to rebound when treatment intervals were longer. These findings provide authorities with practical evidence to plan treatment schedules and make efficient use of their resources.
The task is now to prepare for next spring. Effective prevention requires early action and coordinated efforts across public and private spaces. The canton and municipalities already take measures to control breeding sites in public areas, including treating catch basins to kill mosquito larvae. Residents can support these efforts by removing standing water from balconies and gardens and thoroughly cleaning containers to remove mosquito eggs attached to their surfaces. For standing water that cannot be removed, such as in catch basins on private property, residents can obtain larvicide from the canton. Further information is available on the Canton of Basel-Stadt’s website.
For Basel, the challenge is to achieve lasting reductions in Asian tiger mosquito populations. Continued field and laboratory research can help identify the most effective combinations of control measures under local conditions, while ongoing monitoring allows us to assess their effects across neighbourhoods over time.
However, scientific evidence alone is not enough. Keeping tiger mosquito populations under control requires sustained, coordinated efforts by authorities and residents alike. Our success in tackling this growing challenge will depend on how determined and consistently we act, both in preparation for next spring and in the years to come.”
Contact for media requests: communications@swisstph.ch
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