Skip to main content

Insect repellents could actually increase mosquito numbers and killer viruses such as Zika

  • Scientists say ingredient picaridin kills the predators that feed on their offspring
  • This happens because the chemical can enter waterways through sanitation 
  • Specifically, it affects spotted salamanders which live off a mosquito larvae diet
  • Food chain actively helps to keep Zika-carrying mosquito populations in check 

On the increase? Insect repellents used to deter mosquitoes could actually lead to an increase in their numbers - and the diseases they carry.

The findings were published in the Biology Letters journal.

Dr Rafael Almeida, lead author, said the effects of repellents containing DEET and picaridin need to be studied further.

However, writing in the journal he specualted it could 'potentially increase mosquito-borne disease risk worldwide.'

Dr Almeida said: 'The amount of repellents entering waterways peaks seasonally.

'If amphibians are exposed during a sensitive life stage, entire cohorts could perish. The population would not have a chance to recover until the following year.

'Meanwhile, mosquitoes would continue to reproduce. It suggests a negative feedback loop.'

Spotted salamanders: The lizard-like predators begin life in the water where they provide natural mosquito control, foraging on the insects' larvae

Researchers tested the effects of two of the most popular insect repellents - DEET and picaridin - on both larval salamanders and mosquitoes.

They exposed them to three different concentrations of these chemicals in a lab, as well as a control treatment.

The mosquito larvae were not affected by any of the treatments when they matured.

Conversely, the salamanders of all three treatment groups began showing signs of impaired development, such as tail deformities.

These occured just four days after they were exposed to the repellent containing picaridin.

More than three weeks after the experiment, up to 65 per cent of the salamander larvae that were exposed to picaridin died.   

Dr Barbara Han, study co-author and a disease ecologist at Cary Institute, said: 'The expediency of salamander mortality was disconcerting.

'When studying the effects of a chemical on an amphibian, we usually look for a suite of abnormalities.

'We couldn't collect these data because the salamanders died so quickly.'   


Almeida RM, Han BA, Reisinger AJ, Kagemann C, Rosi EJ.  2018.  High mortality in aquatic predators of mosquito larvae caused by exposure to insect repellent. Biology Letters. 14(10):20180526

More on this topic