What Chemicals Are Used to Spray For Mosquitoes in St. Louis County?

It's a question 'Patch' readers wanted to know, so we asked the St. Louis County health department and this is what we found out.

 This week, the St. Louis County Department of Health announcement that

The victim is reportedly a 55-year-old woman from Kirkwood who suffered West Nile symptoms, but has since resumed normal activities.

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The news came one week 

Patch then received emails from readers asking what is actually being sprayed into the air to combat mosquitoes. According to John Shelton, spokesperson for the St. Louis County Department of Health, the product is called Aqua Reslin, it is manufactured by ADAPCO and more information can be found on their website

Drew Hane, operations manager with the St. Louis County Department of Health Vector Control & Veterinary Services tells Patch that all spraying is done by St. Louis County Vector Control and it is all "supervised by an employee who is licensed with the Missouri Department of Agriculture as a Certified Public Operator."

Hane stated in an email that the spraying covers unincorporated St. Louis County, plus the county contracts out to a number of cities within the county to provide services. Residents are advised to check with their municipality to determine if it is sprayed by their city or St. Louis County.

As far as the spray itself, Hane stated that St. Louis County only uses EPA approved and regulated insecticides. 

"We use them within the label restrictions and utilize top of the line technology to assist us in providing accurate usage.  Our spray machines are ULV (Ultra Low Volume), the insecticide is pre-diluted with water at the pumping station before being placed in the spray trucks, the spray trucks use GPS technology to determine the speed of the vehicle and the sprayer adjusts the output to 1 ounce per acre (the recommended application rate)," Hane stated in an email.

In addition, Hane provide Patch with the following information on the chemical being sprayed into the air throughout our neighborhoods.

Short Description:

AQUA-RESLIN® is a mosquito adulticide that is highly effective against various mosquito species. It has permethrin and the synergist piperonyl butoxide (PBO). AQUA-RESLIN utilizes the unique patented FFAST formulation that allows the product to be diluted with water rather than oil.

Active Ingredient:


Mode of Action:

Permethrin is a common synthetic chemical, widely used as an insecticide, an acaricide, and as an insect repellent. It belongs to the family of synthetic formulations called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to harm most mammals or birds. It generally has a low mammalian toxicity and is poorly absorbed by skin. AQUA-RESLIN is a synergized Permethrin (synthetic pyrethroid) formulation. The synergist piperonyl butoxide (PBO) aids by allowing the formulation to act faster and use less permethrin in doing so. AQUA-RESLIN is designed for application as an Ultra-Low Volume (ULV) aerosol to control adult mosquitoes and flies in residential, industrial, urban, recreational and other areas where adult mosquitoes and flies are found. The formulation greatly reduces the evaporation rate of water from the droplets and allows the water-based spray cloud to behave as that produced by a typical oil-based formulation.

Where/When to use:

AQUA-RESLIN is used for control of annoyance flies and mosquitoes, mosquitoes and flies of public health or disease vector importance in areas such as residential, industrial, and urban areas.


  • Unique patented formulation allows dilution with water rather than oil and yields a true water based formulation.
  • Fast and effective control of adult mosquitoes.
  • Provides quick knockdown and effective control of mosquitoes, black flies, gnats, biting and non-biting midges as well as other biting flies.
  • For aerial, ground, and barrier application.
  • May be applied undiluted or diluted in water.
  • ULV application provides excellent control at rates up to 0.007 pounds permethrin per acre.


Bayer Environmental Science

The St. Louis County Department of Health website offers a general spraying schedule and specific spray routes will be available each evening by calling the hotline at 314 615-4BUG (314 615-4284). Residents can also visit the county's website or contact St. Louis County Vector Control at 314 615-0680 for more details on mosquito prevention.The Vector Control Office number is 314-615-0680, but residents will likely have to leave a voicemail and await a returned phone call.


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