Spotlight: Resistance Management Program at Benton County Mosquito Control 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.

In the Northwest region, we interviewed Angela Beehler, District Manager at Benton County Mosquito Control District (BCMCD). Two days after completing her degree at North Dakota State University, Angela remarks “Go Bison,” she started working as a seasonal employee at Metropolitan Mosquito Control District in Minnesota at the Rosemount field office. She tells us that it was “love at first dip.” The Benton County Mosquito Control District was established in 1957. It covers 350 square miles of south-central Washington, an area better known for producing nuclear waste than mosquitoes, and serves just over 200,000 people.

Benton County MCD

Angela also provides an interesting piece of information about Benton County, “When I first moved here, people kept asking if I worked at “the area”. What is this, Roswell? Come to find out it’s the Hanford Site, part of the Manhattan Project of World War II, where they irradiated uranium for the atomic bomb. I probably should have researched this before I decided to raise my children here, but fun fact, Benton County houses 60% of high-level radioactive waste by volume managed by the US Department of Energy and 7–9% of all nuclear waste in the United States.” How crazy is that? Too bad the mosquitoes weren’t irradiated out of the area permanently!

The convergence of the Yakima and Columbia Rivers in Benton County brings beauty to the area, but it also creates mosquito habitat that must be treated regularly. Combined with pressure from the area’s agricultural industry – the Columbia Valley is well known for producing grapes, hops, cherries, and apples – the potential for pesticide resistance is high. Resistance management was fully incorporated into the BCMCD plan in 2017.

NWMVCA Spring Workshop

BCMCD is a well-established district and fortunately has terrific community support. Because of this support, and some forward-thinking staff, Benton County was able to build a facility large enough to host the Northwest Mosquito and Vector Control Association’s annual Spring Workshop multiple times over the last decade. Through that program, experts such as Jack Peterson of Rutgers University, was brought in to provide bottle bioassay training. Resistance management training is a regular component of the Spring Workshop agenda and likely always will be. Angela comments, “BCMCD benefits because the attendees learn to conduct the tests on our mosquitoes – free labor!”

BCMCD’s Approach to Monitoring and Managing Resistance

When it comes to the resistance management program at BCMCD, everyone plays a role. Angela expresses, “I can’t say enough good things about my team. From the person that takes the complaint calls to the one planning where to trap and treat each night, everyone plays their part. As long as we are all communicating, we just might survive until the next October. For those of you that don’t have a season that ends in October for an annual do-over, I’m sorry. We count on it for our sanity, and the natural resistance management!”

“Even though BCMCD was rotating products regularly, we weren’t concerned about resistance in our local populations of mosquitoes until we noticed a lack of efficacy in our control methods in 2017. If we weren’t actively monitoring for resistance, we easily could’ve missed it.”

Adult Resistance Program

BCMCD prevents resistance by rotating pyrethroids (by ground) and organophosphates (by air) about 3 times per year. Since 2009, when West Nile virus was at its peak, the district has contracted with Vector Disease Control International for the aerial application of adulticides.  At the time, Angela, Dan Markowski (VDCI), and Annie Moser (Grant County MCD) tested several products using caged mosquitoes and droplet testing equipment to determine which product and rate would deliver the best results in their unique environment.

In 2017, based on trap data and resident calls, sufficient knockdown of adult mosquitoes was not being achieved after truck-mounted fogging. To train their team in resistance monitoring, Angela says, “we sent one of our surveillance employees, Kristen Campbell, to Mississippi to participate the Centers for Disease Control and Prevention’s resistance training workshop led by Janet McAllister. Kristen was given this amazing opportunity with one catch; she had to regurgitate the training to anyone willing to attend from the Pacific Northwest.” Of course, Kristen obliged and put on a workshop where a number of people from around the NW ran bottle bioassays using our mosquitoes and helped BCMCD to identify possible pyrethroid resistance in their Culex populations. “As a result, we set up a field trial for June of 2018.  We had been using the same product for over 10 years; probably time to mix it up,” Angela continued.

“Early June of 2018, week ONE of Steve Ingalls triumphant return to BCMCD, representatives from ADAPCO, Clarke, Central Life Sciences, and Leading Edge all came to assist with our resistance management trial. Duet, Zenivex®, Fyfanon®, and DeltaGard® were put to the test on the same night, with me aspirating mosquitoes back at the office like a fiend. Based on the results of the trial, label specifications, and chemistry, we felt confident adding Fyfanon® and DeltaGard® to our ground program. Note* Washington state and federal NPDES regulations Endangered Species habitat, and specialty crops play a big role in our product selection, so read your labels!  That’s my regulatory plug – only one,” Angela promises. We all appreciate your regulatory experience, Angela!

Larval Resistance Program

Angela regards having Steve return to the district as Field Supervisor is a “blessing” that she is grateful for every day. His extensive experience in mosquito control, and his time as a product representative allows him to quickly recognize when it’s time for rotation in our larvicides. Previously, BCMCD has had issues with larviciding efficacy in sewage lagoons, but Angela believes that is likely “attribute(d) more to pollution than resistance.” She asks of her fellow peers in mosquito control, “If anyone has a silver bullet for sewage lagoons, let me know!” In the storm drains located in Benton County, staff rotates (S)-methoprene, Bacillus thuringiensis/Bacillus sphaericus and spinosad to prevent resistance, based on reports of other districts who were having problems.

Sewage lagoon

In addition to traditional methods of insecticide resistance, Benton County has expanded their equipment and capabilities in the last couple of years. Angela shares about this experience: “One day while driving to work late in 2019, I got a call from the Washington Department of Health. The message was something along the lines of “the arbovirus branch has been reassigned to homelessness and climate change; can you store the polymerase chain reaction (PCR) testing equipment so it gets used for its intended purpose (vector control)?” I enthusiastically agreed. Keep in mind, I knew/know nothing about running PCR, and neither did anyone in our office. Bringing this valuable equipment back to life and putting it to good use in 2021, Kevin Shoemaker, BCMCD’s Assistant Manager, hired Jasmine Che to produce a genetic profile of our mosquitoes, so we can monitor change over time, and use this information to drive our resistance management program.”

Operational Application of Resistance Management Program

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

She shares, “Anecdotally, I’ve observed that we must use different products by ground and by air throughout the season when we have peak numbers of mosquitoes or West Nile virus positive pools. If we do not rotate products, we’re sending crews out night after night for ULV spraying, which is a strain on all our staff. We utilize the same employees for larviciding as we do for adulticiding, so every late night that a crew member is out takes away from our larviciding operation. I also recognize the time spent fielding repeat complaint calls from residents, retesting trap samples, and reinitiating ULV treatment routes is much lower after we rotate pyrethroids with organophosphates. Do it right the first time, and you and your staff will be much happier.” Angela’s take on this makes me think of the quote, “An ounce of prevention is worth a pound of cure.”

Challenges to Resistance Monitoring and Advice to Get Started

Before discussing the challenges that BCMCD has encountered, Angela shares, “I said I wouldn’t bring up regulations again, but I lied.” Their biggest hurdle in adding organophosphates into their rotational plan with DeltaGard® was their NPDES permit. Deltamethrin was not listed on the permit because it was previously registered as a barrier spraying product and thus isn’t labeled for use near water. In addition, malathion was identified in Washington as “emergency use only”. She continues, “renewal periods are typically every five years, so if an active ingredient is not listed, you may need to wait to use new technology. The 2019 Washington NPDES permit nearly stated that mosquito control programs could only use deltamethrin after documenting resistance. Thanks to help from Bayer and ADAPCO that was not the final decision. It’s important that mosquito control programs comment on this type of language during permit renewal cycles and try to get it removed, because it can be restricting and damaging when you’re combating pesticide resistance.”

The advice that Angela would offer to those interested in establishing a resistance management program is:

“Every program needs to have a resistance plan. I was amazed and horrified to see that our mosquitoes were not dying the last time we ran a bottle bioassay. Why would you go through the trouble of planning and executing a ULV treatment if it’s not effective? Testing materials are readily available and easy-to-use, plus it’s a fun project for staff who are interested in the science of mosquito control. My advice to programs wanting to establish a plan is to contact the CDC and ask for help. The CDC cannot shoulder the burden of monitoring and managing resistance on their own. If we all contribute data, we make a stronger case to the EPA that new tools are needed to combat mosquitoes, which leads to research, jobs, and more treatment options.”

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.

Have Questions? We’re here to help!

ADAPCO, an Azelis company, has entomological and technical experts that will work with you to identify the appropriate solution to control nuisance and vector mosquitoes in your region. Our mission is to assist you with preserving public health.

Talk to one of our experts to get started today!

Contact an Expert Today