Insect Repellents May Be Increasing Mosquito Populations

By John Fraser

The use of chemical insect repellents internationally is both increasing and adversely affecting the development of salamanders exposed to the deterrent, a recent study uncovers. Emma Rosi, co-investigator of the study and an ecologist at the Cary Institute of Ecosystem Studies, explains the routes and prevalence of toxic agents in the environment: “Chemicals in repellents enter aquatic ecosystems through sewage effluent and are now common in surface waters.” Exposure to contaminated water sources occurs because salamanders are amphibians and an ‘aquatic juvenile phase’ is necessary to their development. The stage of growth spent primarily in water is also the main point of the salamander life cycle where mosquito larvae are consumed.

Researchers tested the effects of exposure to picaridin, a chemical agent commonly found in mosquito repellents, on both mosquito and salamander larvae. Picaridin appeared to have no impact on the mosquito larvae, but demonstrated a significant amount of harm towards the salamander population: “After four days of exposure to replant with picaridin, salamanders in all of the treatment groups began to display signs of impaired development such as tail deformities. By day 25, 45-65% of picaridin-exposed salamander larvae died.” Considering the dominating role that insects play as vectors of disease transmission, the consumption of mosquito larvae by salamanders is a key contributor in keeping the mosquito population in check. The introduction of picaridin-containing mosquito repellent into an ecosystem may then actually lead to an increase in the prevalence of mosquitos as salamanders, their natural predator, are killed off.  

Cary Institute of Ecosystem Studies. (2018, October 31). Widely used mosquito repellent proves lethal to larval salamanders: By harming mosquito predators, picaridin may help mosquitoes survive. ScienceDaily. Retrieved November 12, 2018 from www.sciencedaily.com/releases/2018/10/181031080627.htm