Insect repellents used to deter mosquitoes could actually lead to an increase in their numbers – and the killer diseases they carry.
Researchers now fear a commonly-used ingredient in over-the-counter products is altering the food chain.
They believe sprays and lotions containing picaridin can kill spotted salamanders, which feed on a mosquito’s offspring.
In turn, their absence allows the fly’s population to boom, subsequently
raising the risk of Zika and dengue fever infections.
The findings, made by experts at New York’s Cornell University, 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.’
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.’