Spotlight: Resistance Management Program at Toledo Area Sanitary District

You may feel like the topic insecticide resistance is dynamic, complex, and ever evolving. In many ways, you’re right. As a vector control professional, you are challenged operationally every day to overcome resistance and successfully control mosquitoes. While this may be a new topic to some of us in vector control, it is a common theme across several entomological fields (such as agriculture and apiculture). To support you in your efforts to control mosquitoes, ADAPCO works to gather information and resources to better support your program’s needs for resistance monitoring and management.

So, what do you do if you think there is insecticide resistance in your area? How do you monitor for it and respond to it when it’s detected? With such an important topic, we wanted to take the opportunity to highlight programs in various regions throughout the US that have developed a resistance monitoring and management program to help them better control mosquitoes.

Resistance Management Toledo

In the Midwest region, we interviewed Paul Bauman, Biologist & General Manager at Toledo Area Sanitary District (TASD). Paul gives all the credit for his involvement in mosquito control to his advisor at Bowling Green State University, Dr. C. Lee Rockett.

“As an undergrad, I took a medical entomology course with him as the instructor, and I was hooked! I did well in the course, and he offered to take me on as a graduate student. He truly fostered my interest in medically important arthropods and was the first to impress upon me the importance of integrated management practices. After graduate school I worked with our local health department and was the resident “bug guy”. I served on the advisory board for the Toledo Area Sanitary District (TASD), our local mosquito control district, during my time at the health department. When the District’s Biologist decided to retire, I was asked to take his place. In 2017, after about three years as the Biologist, I was promoted to General Manager of the District.”

Toledo’s program is responsible for 600 square miles and protecting 475,000 citizens, within Lucas County, Ohio, from the nuisance and public health threat of mosquitoes.

Toledo Area Sanitary District
Lucas County Ohio

Resistance Management at TASD

Resistance management was incorporated into the TASD’s plan in 2014, after Paul’s first season at the District. There were a number of factors that contributed to the need to start the program, such as the historical lack of good product rotation practices and public pressure against the use of insecticides that questioned their efficacy. It was important to determine if the local mosquitoes were susceptible to the products being used after years of exposure. It was also critical to TASD to assure citizens that were cynical of TASD’s practices, that they were measuring mosquito susceptibility regularly. Since establishment, TASD has relied only on district funds to support a resistance management program. Paul even states, “It is an extremely affordable program to get started and maintain. I believe we were able to start a bottle bioassay program for less than $150.The most expensive start-up cost was a luxury purchase of a HEPA filter mouth aspirator.” Bottle bioassay testing kits are currently available for FREE from the CDC to get you started!

TASD’s Approach to Monitoring and Managing Resistance

TASD’s Science Division, consisting of the Biologist, Education & Research Coordinator, and seasonal lab staff oversee the resistance monitoring program. When the need arises for specific management strategies to be implemented, the Science Division consults with Paul, to determine the best strategy to reduce the mosquito population in question and reduce any further resistance development. Treatment recommendations then get passed on to staff for application instructions.

“The (resistance management program) began during the 2014 mosquito season. Previously, there wasn’t much of a plan in place and product choice was based solely on price and perceived efficacy.”

Adult Resistance Program

Toledo’s current resistance monitoring program is focused primarily on adult mosquito susceptibility. They utilize the CDC bottle bioassay methodology to test adult mosquitoes at the start of the control season, and at least monthly within the season to look for changes in susceptibility.

CDC bottle bioassay

In addition, anytime a control application does not obtain the desired efficacy, they will also do a bioassay to assess if resistance could have been a factor. For typical rotational management throughout a season, they will rotate products on approximately a month-to-month basis. Over successive control years, using synthetic pyrethroids with and without synergists and organophosphates is another means of implementing rotational management. If resistance is suspected in a population, either they will change the active ingredient, mode of action, or increase the application rate.

Operational Application of Resistance Management Program

With all the resistance management techniques that TASD uses, I wanted to understand how it translates into operational use in Paul’s program.

“In terms of our mosquito population composition and susceptibility, we identified some low-level resistance to organophosphates that helped guide a change to more pyrethroid use in certain areas of the county when targeting Culex mosquitoes. This is a change we may not have identified without resistance testing and was important for our efforts to protect our citizens from West Nile Virus.

Overall, our program has changed a great deal since 2014, when we started resistance testing. Technology advancements and increased surveillance sites along with trapping frequency have allowed us to gain a much better understanding of what is happening within our mosquito populations in response to our treatment efforts. Resistance testing provides additional information for us to consider when making product selections, application rates, or when evaluating the overall efficacy of control applications.”

Paul discusses further why insecticide resistance monitoring is so critical for his local populations and why it’s necessary for all mosquito management programs. “I think the biggest benefit of monitoring for resistance coincides with being good stewards of pesticide use. As an organization, and our industry in general, we strive to be targeted, judicious, and successful with our pesticide applications. We don’t want to put control products into the environment that will not be successful in their purpose. This undermines our operational credibility as an organization, is not fiscally responsible, and is just a poor environmental practice. Monitoring for resistance helps to assure, as much as possible, that our use of pesticides has the greatest potential for success. Resistance monitoring provides vital information we can use to improve our services for our citizens while being an environmentally responsible organization.”

Challenges to Resistance Monitoring and Advice to Get Started

In Paul’s opinion, the biggest hurdle to their resistance management plan is the lack of different modes of action in adult control products. Identifying a problem or an emerging issue is quite simple, but the lack of available adulticide chemistries is concerning, and sometimes feels limiting and as though they don’t have anywhere to turn to get the desired control outcomes. Paul shares:

“I am a big believer in the importance of resistance monitoring and management practices.  It would be extremely beneficial if every program that uses pesticides monitored the susceptibility of the pest it is targeting to the control products being used.”

The advice that Paul would offer to those interested in establishing a resistance management program is: “The best way to start a monitoring program is to simply just do it! If needed, ask for help or guidance from another program that has experience with the testing. It is not difficult or expensive. You simply have to make a commitment to learn the procedure and do it!”

As you can see, there is not one simple answer when it comes to tackling and responding to insecticide resistance. Let the capabilities of your vector control program, your local mosquitoes, and the needs of your constituents drive what your insecticide resistance management plan looks like. Identifying the problem and taking small steps to combat resistance is better than no attempt at all.

~Written by Emily Boothe
Technical Development Specialist, ADAPCO

ADAPCO would like to note that the CDC is currently offering free bottle assay kits: Programs in the continental United States and its territories can order free Insecticide Resistance Kits by sending an email to and requesting an order form. Kits include bottles, insecticide, and manual.

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