Pesticide Resistance in Mosquitoes

Teton County Weed and Pest District’s Entomologist, Mikenna Smith, together with scientific staff from Valent Biosciences will be conducting a mosquito “field cage trial” this month. Field cage trials are large scale, field experiments where mosquitoes are placed in cages that are strategically placed in the path of a truck mounted ultra-low volume adulticide spray drift. This is the most “real world” experiment that can be conducted to determine if certain pesticides can kill the caged mosquitoes.

In 2022 and 2023, Mikenna discovered that a local strain of the Western Encephalitis Mosquito, Culex tarsalis was showing significant resistance to multiple types of pesticides under laboratory conditions. A major element of integrated mosquito management (IMM) is insecticide resistance and efficacy testing, to determine if the insecticides the District is using are actually effective at killing mosquitoes. This is because insecticide resistance is a major problem in many mosquito species worldwide, resulting in difficulty for mosquito control districts to manage these mosquitoes. This is especially concerning when these mosquitoes are a vector species, one that is capable of transmitting a pathogen such as West Nile Virus that can cause disease in humans and horses. As such, Mikenna and Valent Biosciences will be taking the preliminary laboratory resistance data and putting those same mosquitoes to the test under field conditions to determine the significance of their resistance under real world conditions, as well as testing a new pesticide against these highly resistant mosquitoes.

We will continue to monitor pesticide resistance regionally and provide updates to the community on our findings from the field cage trails.

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