2018 Mosquito Update


Every summer the Teton County Weed & Pest District dedicates highly trained staff to study the effectiveness of our mosquito treatments in the Teton County region. We treat mosquitoes to reduce potential human health risks, as well as to reduce the overall nuisance mosquito population. Surveillance of adult and larval mosquitoes supplies detailed information on where and how we need to focus our management efforts.

2018 Mosquito Results

  • 240 adult mosquito traps were set throughout the summer
      • 27 different species from 4 genera were collected
      • Mosquito numbers peaked during the last week of June and stayed high through the first two weeks of July

A Comparison of Adult Mosquitoes Caught by Week from 2016 – 2018

The week number is along the X-axis. The first Y-axis shows the number of mosquitoes caught, and the second Y-axis shows the number of traps set.  The circles show the number of traps set each week from 2016 – 2018, and the columns represent the total number of mosquitoes caught by year. Equal trapping effort has not been applied across weeks or years. Weeks with greater numbers of traps did not always yield higher numbers of mosquitoes. The graph suggests that mosquito populations were similar in 2016 and 2018, and that a greater number of mosquitoes were produced in 2018.

For reference, the 21st week in 2018 was the fourth week of May and the 37th was the 3rd week of September.

2018 Results, Continued

  • Over 5,000 larval sample points were collected.
      • A sample point is when a dipper is used to visually check a water sample for the presence or absence of mosquito larvae. TCWP collects samples of mosquito larvae from various habitat types throughout the summer and brings samples back to the TCWP lab to rear them into adults.
      • Reared 2,613 mosquito larvae into adults. This information allows us to build relationships between habitat and preferences of mosquito species.
  • We made eight adulticide runs throughout the 2018 summer (adulticide: use of fog trucks to combat large mosquito populations). 
      • Decisions to utilize adulticide are based on adult mosquito surveillance including the number of mosquitoes we collect, the species, and the neighborhood where we collect them.
  • Culex tarsalis is the mosquito species we are most concerned with in Teton County due to its competency as a vector for West Nile virus.
    • We target this species as much as possible for all our management efforts throughout the summer.
    • TCWP tested 61 mosquito pools for West Nile VirusAll tested mosquito pools were negative. All of the Culex tarsalis collected from the same trap on the same day were tested together.
    • In contrast to the general mosquito population, Culex tarsalis mosquito populations peak later in the summer.

Comparison of the number of collected adult Culex tarsalis mosquitoes across years by week number.

Our lab manager, Mikenna Smith, performed crucial pesticide resistance testing this summer. Pesticide resistance testing assesses the levels at which the mosquitoes are resilient to our current pesticides allowing us to ensure that the mode of action used by the pesticide we are applying is still effective this year. None of our tested mosquito populations have shown signs of pesticide resistance to date.

Though the summer mosquito field season is complete, the TCWP team will spend the winter reviewing and analyzing all data collected in 2018. We will use this data in combination with knowledge gained in previous seasons to formulate a mosquito management plan for summer of 2019.