Spotlight: Resistance Management Program at Tangipahoa Mosquito Abatement 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 southeast region, we interviewed Dennis Wallette, Director for Tangipahoa Mosquito Abatement District (TMAD). After graduating with a degree in biology and a minor in chemistry, Dennis did some research and development work in the Baton Rouge area before applying to be a biologist with the East Baton Rouge Mosquito Abatement and Rodent Control (EBRMARC).

“The truth is that when I took that job in mosquito control, I did not anticipate staying there for more than a few years. I thought I would get some supervisory experience in my field of study and would move on to something else. However, I found that I really enjoyed the work and the close relationships that I formed with others within the industry. I never left.”

While working at EBRMARC, Dennis earned his masters in entomology and eventually had the opportunity to start a brand-new program in Tangipahoa. Dennis has served as the director at TMAD for 18 years of his total 31 years in mosquito control.

Tangipahoa MAD’s Approach to Monitoring and Managing Resistance

Interestingly, Dennis was among some of the earliest adopters of the CDC bottle bioassay method for detecting insecticide resistance. During his time at EBRMARC, they began using this assay to assess resistance and he continued doing CDC bottle bioassays when he became the director of TMAD.

This is now managed by their assistant director, Colby Colona. The consistent monitoring of insecticide resistance throughout the parish means that not only does TMAD know what products are most efficacious against their mosquitoes, they also know how these trends have changed over time.

To supplement the data they get from the CDC bottle bioassay, which is a laboratory assay, TMAD will also conduct field cage trials to determine product efficacy in a more “real world” environment. These field trials are an “all hands on deck” effort where most members of the TMAD team participate. By conducting these trials, Dennis and his team have more information and data to base their operational decisions on.

CDC Bottle bioassay prep
Field trial

Because Dennis and his team have been doing resistance monitoring so routinely, they have managed to prevent its development in their area with the exception of some documented resistance to pyrethroids in Culex quinquefasciatus. The low prevalence of resistance in TMAD’s parish likely has to do with their rotation protocols for adulticides.

Dennis shared that since TMAD was created, rotating chemical classes used for ground ULV adulticiding has always been part of the program.

“Most years, we begin the season and end the season with an organophosphate. In the past, that was generally malathion concentrate (Fyfanon ULV). We also used chlorpyriphos in that role for a few years. Lately, our organophsophate of choice is the water emulsion formulation of malathion (Fyfanon EW). As we approach West Nile season, we shift to some of the “premium” synthetic pyrethroids. Those are the products that have a quick knockdown and with which we still observe high mortality in our cage tests. A few years ago, we discontinued using the various generic formulations of permethrin altogether because of what we were seeing in our CDC bottle bioassays. In our aerial program, we have exclusively used naled (Dibrom).”

In summary, TMAD utilizes laboratory and field assays to assess the resistance status of their mosquito populations. This combination of assays allows TMAD to have a detailed and dynamic understanding of their local mosquitoes and how to best control them while also being good stewards of the limited chemical toolbox available.

Operational Application of Resistance Management Program

With such a wealth of resistance information on their local mosquito populations, it’s important to understand how that information is translated into operational control. Through the continued surveillance of resistance Dennis has observed “the development over time of a tolerance to synthetic pyrethroids. This is obviously of great concern to us.”

So once the tolerance and/or resistance has been detected, how do you respond to prevent it from getting worst? Dennis’s strategy was to change the timings of their chemical rotation. “We have increased the windows at the beginning and the end of the season which we utilize OP’s in our operations. Rotating chemical classes is the only way to prolong the efficacy of the products in our increasingly limited arsenal.”

An integrated vector management approach is also key to preventing the development of insecticide resistance in local mosquito populations. Tangipahoa MAD also does an exceptional job of having a well-balanced program that incorporates educational components, source reduction, biological control, and larviciding. The implementation of these additional mosquito control tactics reduces reliance on adulticides and insecticide exposure to mosquitoes.

Rotate chemical classes

When asked what the biggest benefit was to conducting insecticide resistance monitoring and management, Dennis responded: “Being proactive with resistance management allows you to see the beginnings of tolerance and resistance in area mosquitoes. Without this knowledge, you might be inclined to continue with your current practices blindly without realizing that you are even having a resistance problem.”

Challenges to Resistance Monitoring and Advice to Get Started

When asked about the challenges that might prevent someone from starting their own resistance monitoring program, his response was very optimistic. It’s nothing that most programs can’t handle!

“Implementation of a resistance management plan is really very affordable. The initial outlay for supplies is minimal and should not be an obstacle for most programs, and each test only takes a few hours to run. It should be viewed as a necessity instead of a luxury.”

Through the years, increasing amounts of attention have been paid to insecticide resistance. Now that more and more places are regularly monitoring for it, we understand more clearly than ever just how widespread the problem is. The problem of insecticide resistance demands that we respond to it, otherwise, the efficacy of our limited chemical toolbox will steadily decline until they are no longer a viable option.

With more resources being dedicated to insecticide resistance monitoring, it’s the easiest it’s ever been to start monitoring for resistance. The CDC offers CDC bottle bioassay kits for free and have extensive training resources on how to get started. Once you have an idea of what your local mosquito population’s resistance profile looks like, you can begin to expand your testing capabilities and respond in a way that improves the efficacy of your efforts. Dennis also said, “I would advise to reach out to other Districts for help. Chances are that a nearby program is already doing these things and I would wager that they would provide a willing resource to help get you started.”

Dennis Wallette

But the big question would it make a difference if more vector control programs had a dedicated resistance management plan? Dennis’s opinion is: “Without question. Being aware of an existing or developing resistance problem is critical in deciding which pesticides to use at any given point during the year and when to rotate to a different product. The number of pesticides available to mosquito abatement districts small enough as it is. We must do all that we can to protect the efficacy of those pesticides, and the way to do that is by having a well-thought-out resistance management plan.

As you can see, there is not just one right 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 even a small step to combat it is better than no attempt at all.

~Written by Casey Crockett, PhD
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 USBottleAssayKit@cdc.gov and requesting an order form. Kits include bottles, insecticide, and manual.

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