Spraying insecticides on grass and bushes to protect against the spread of mosquitoes is rarely done by the government; it usually falls to homeowners. In many areas, there are no government programs to spray for bugs. That means mosquito populations can vary from neighborhood to neighborhood.
Researchers at North Carolina State Univ. looked at mosquito species in Raleigh to see what species lived in what neighborhoods. They gathered mosquitoes from 31 residential areas in Raleigh. They covered areas from modest homes to ones worth more than two million dollars.
Wealthier neighborhoods were more likely to have pesticide-resistant mosquitoes. “Homeowners with money will pay to spray for mosquitoes, which selects for localized resistance,” said Prof. Martha Burford Reiskind, who was a corresponding author on the study.
The higher the value of a home, the more resistant the mosquitoes were. On average, for a house worth $350,000, one out of every five mosquitoes was pesticide-resistant. For a home with a value of $720,000, about half the mosquitoes were pesticide-resistant. If a house was worth $1.5 million, more than four out of five mosquitoes were resistant. But, on the other hand, while the mosquitoes they found were hardier, there were fewer of them overall — because of all the spraying.
The study took place between 2016 and 2024. In 2016, no mosquitoes had the genetic mutation that made them resistant. It didn’t appear until 2018 in a wealthy neighborhood. And, by 2022, every site had at least one mosquito with the genetic mutation. The resistance spread quickly because spraying helped it — killing the bugs without the gene so those with it were the ones to breed.
Areas with continuous spraying, like South America and Asia, have documented pesticide resistance fueled by spraying. America is the first documented place where resistance is being caused by private spraying.
Like all studies, the research has limitations. It happened exclusively in Wake County, North Carolina. The results may not be the same in places with different weather, spraying habits and mosquito populations or species. The researchers only looked at one mutation in one gene — there could have been other reasons the mosquitoes were surviving. The study also did not measure how much pesticide residents used, just whether or not they were spraying.
Researchers said that they aren’t saying to never use insecticides. Insecticides are a tool that should be combined with other ways of managing insects to prevent overuse. Stopping mosquitoes from ever breeding is an essential first step. Mosquitoes breed in stagnant water. Making sure buckets, toys, gutters and flowerpots aren’t collecting water is crucial. If you have a bird bath, check it regularly for any signs of mosquito larvae.
Bug repellent on skin and clothes helps prevent bites from bugs that are around you. A lot of research questions the efficacy of DEET; however, it’s only ever been shown to lose potency in labs, not in the real world.
“People should understand that Deet does not lose its effectiveness through normal use, but only under specific laboratory conditions designed to reveal how it works on mosquitoes,” said Prof. Claudio Lazzari, from the Univ. of Tours.
