Relative Effectiveness of Insect Repellents Among Infected and Non-Infected Mosquitoes

Though the weather outside is frightful, it’s difficult not to dream of the warm days ahead. Thoughts turn to gardening, hiking, swimming, and just being outside in the warm sunshine, but you should also be mindful of the pests associated with the warm weather. Warms days and nights bring ticks, mosquitoes, and public health risks related to these pests. If you watch the news, you’re already aware of diseases transmitted by blood-sucking pests, especially ticks and mosquitoes. While such news stories may have you reaching for a can of repellent, a recent study involving mosquitoes suggests the effectiveness of insect repellents could be contingent on whether or not a given mosquito is infected.

As federal officials are warning of an emergent disease threat from a mosquito-transmitted virus, Eastern Equine Encephalitis (EEE)*, I read of a class study by an associate professor Marc Lajeunesse and several of his students from the University of South Florida, regarding the effectiveness of insect repellents. The study asked the question, ‘Do infected and non-infected mosquitoes show different responses to insect repellents?’

Rather than conducting original field studies and exposing subjects to disease, the students screened 2,316 existing research studies and identified 13 studies that had data that could be used for their analysis. They looked at seven different repellents (including DEET), six different mosquito species (including Aedes aegypti), and various infectious agents transmitted by mosquitoes, including malaria, dengue, and Zika virus.

Overall, the pooled data showed that most disease-infected mosquitoes were less responsive to repellents than uninfected mosquitoes, with the exception of those carrying malaria. A secondary finding was that older mosquitoes were less sensitive to repellents than were younger ones. Click here to read the full study.

More research is needed to confirm these results, and the study doesn’t suggest that you shouldn’t use repellents, but it is worrisome if the infected mosquitoes that need to be repelled the most may be repelled the least.

What this study means to me is that an overall approach to vector borne diseases requires integrated pest management (IPM). A “vector” of disease refers to pests like rodents, ticks, and mosquitoes. What tools do you have in your IPM toolbox to achieve a desired outcome? Sure, repellents and pesticides are in your tool kit, but it should also include:

  • Situational awareness (avoid tall grass for example),
  • Property management (like proper drainage and correct standing water conditions) keep the lawn properly maintained. Rodents, ticks and mosquitoes love tall grass.
  • Wearing appropriate clothing for the environment you going to be in. If you plan to hike through the woods, you should be wearing light colored long pants and sleeves.
  • Correct structural deficiencies like faulty screens and garage doors, which can allow entry to pests like mice and rats.

As part of an IPM approach to mosquito control, Masters Pest Control offers In2Care Mosquito Control Solutions, which targets a mosquito population at its source by utilizing a larvicide that is carried to breeding grounds by adult mosquitoes. Click here to learn more about the In2Care program.

We’re always touting the importance of preventing bites, since that’s how infected ticks and mosquitoes transmit diseases to people. Personal repellents (usually in the form of a skin or clothing spray) are a main defense, especially against mosquitoes. But that single approach may not be as effective as we expected.

*Eastern Equine Encephalitis (EEE) is not a new mosquito disease, but it is a scary one because it attacks the brain and it has no known cure. Most people show no symptoms of the disease, but for those that do, the mortality rate is high. There was a spike in EEE in 2019, primarily in the eastern and southeastern US. 15 people in 9 states have died as of December 3, and authorities warn the outbreak could move to new regions.