The North Shore Mosquito Abatement District’s Resistance Management Plan: A Holistic Approach to Mosquito Control
How NSMAD’s Integrated Pest Management framework addresses resistance prevention and management in mosquito populations
Insecticide resistance is a dynamic and complex topic that presents a daily challenge to vector control professionals in their efforts to control mosquitoes. While this may be a new topic for some, it is a common theme across several entomological fields. Azelis A&ES recognizes the importance of supporting vector control programs to monitor and manage resistance, and actively gathers information and resources to meet their needs better.
When facing insecticide resistance in your area, it can be challenging to know how to monitor for it and respond appropriately. To shed light on this important topic, we have sought out programs from various regions of the US that have developed effective resistance monitoring and management programs for mosquito control.
The North Shore Mosquito Abatement District (NSMAD) in Illinois has made substantial efforts to develop and implement an Integrated Pest Management (IPM) plan that strongly focuses on resistance management and prevention. In this interview, Dr. Mark Clifton, the District’s Executive Director, discusses the challenges they faced and the changes they have made to ensure the effectiveness of their mosquito control efforts.
The Importance of Resistance Management
Resistance management is essential for the long-term success of any mosquito control program. The emergence of resistance in mosquito populations threatens the effectiveness of existing control measures and can lead to increased transmission of vector-borne diseases.
NSMAD began focusing on resistance management in 2016, as they noticed a reduction in the effectiveness of their treatments. The district now employs a comprehensive strategy for managing mosquitoes, utilizing a range of techniques across the Integrated Pest Management (IPM) spectrum. Dr. Clifton emphasizes the need for a broad approach:
“We approached resistance management from a holistic perspective that utilizes every possible tool along the IPM gradient to reduce mosquitoes, which also reduces reliance on just one chemistry or just one method and so would presumably reduce or prevent resistance as well.”
The district’s resistance management plan has become a central part of its decision-making process, with nearly every position impacted by this focus on resistance prevention and management. As Dr. Clifton states, “In truth though, every single employee plays some role in resistance management. As I mentioned, so many elements of our program had to be adapted to place resistance management in the forefront of our decision-making process that nearly every position is impacted.”
The NSMAD Resistance Management Plan
To prevent resistance, the NSMAD has invested in community-level interventions, such as employing a dedicated communications manager to educate the public about preventing mosquitoes and implementing a service request system where residents can request a domestic inspection for their property. Dr. Clifton stated, “We implemented a Geographic Information System (GIS)-based larviciding program, whereby every source of standing water, down to the size of a tire rut or puddle, is mapped, inspected, and treated regularly.”
The district has also implemented a wide area larviciding methodology for floodwater mosquitoes using VectoLex WDG. Dr. Clifton explained, “Every adult control treatment we must conduct to mitigate the biting from floodwater species such as Aedes vexans simultaneously and inadvertently drives further resistance in Culex pipiens. By adopting a wide area larviciding methodology for species like Aedes vexans, we can minimize the selective pressure placed on vector species like Culex pipiens, thereby preserving the remaining utility of our adult control materials for emergency disease control situations.”
As part of their IPM and resistance management strategy, the district has divided itself into approximately one square mile treatment blocks, each receiving a different treatment regime from adjoining blocks in a checkerboard pattern. Dr. Clifton stated, “In essence, we have created a “refuge strategy” like what is commonly done in agriculture with transgenic corn or other crops. Resistant mosquitoes should have opportunities to mate with susceptible mosquitoes, which should prevent or slow the development of resistance.”
The NSMAD also rotates larval control materials temporally. Dr. Clifton stated, “A product like VectoMax is critical for resistance management due to the ability of Bti to “reset” the larval resistance status of mosquitoes that may be developing resistance to Bs or methoprene. In addition, these products are rotated every season so that no treatment block receives the same treatment for more than one season.”
To ensure the effectiveness of their strategies, the district runs a quality control program called “Back Checks,” where they randomly select catch basins for sampling, and larvae are brought back to the lab, where they are watched and scored for emergence. Dr. Clifton concludes that without this sustained effort to detect, quantify, and mitigate resistance, they could lose any one of the few remaining chemistries they have left.
Collaboration with Research Institutions
NSMAD has also established collaborations with research institutions, such as Loyola University and the CDC Midwest Center of Excellence in Vector-Borne Disease, to help manage their resistance testing efforts. Dr. Justin Harbison of Loyola University conducts bottle bioassays and larval resistance trials with the support of interns or seasonal lab technicians. These partnerships not only provide valuable data for the district but also offer field-based research experience for students. Dr. Clifton highlights the importance of such collaborations: “We try and provide a useful field site for graduate and undergraduate students who want a field-based research experience. Resistance testing is very approachable and not overly technically challenging for students of science, so this has been working for us. However, in the long term, it may become necessary to investigate making some of this a regular full-time portion of our program. Resistance is not going to go away, and even if new products come to the market, we want to assess resistance from the very beginning to ensure we don’t create new resistance.”
Challenges in Implementing Resistance Management Plans
Implementing an effective resistance management plan comes with several challenges. One of the most significant hurdles for NSMAD is the lack of effective rotational tools for adulticiding. In addition, their proximity to O’Hare Airport complicates aerial options due to the high volume of air traffic. Dr. Clifton elaborates on this issue: “While some programs may be able to turn to an aerial capability and use a wider range of OP’s, our proximity to O’Hare airport and its eight runways means there is a tremendous amount of air traffic directly over the district which severely complicates aerial options.”
Another challenge is the human effort required to manage resistance testing of both larvae and adults. While NSMAD has been fortunate to have Dr. Harbison’s part-time support, it may become necessary to incorporate some of these responsibilities into a regular full-time position in the future. Dr. Clifton acknowledges this possibility:
“In the long-term, it may become necessary to investigate making some of this a regular full-time portion of our program. Resistance is not going to go away, and even if new products come to the market, we want to assess resistance from the very beginning to ensure we don’t create new resistance.”
Additionally, the complexity of reworking many aspects of the program to prioritize resistance management presents a major hurdle. Despite these challenges, NSMAD has been successful in adapting its program to place resistance management at the center of its decision-making process.
The North Shore Mosquito Abatement District’s resistance management plan offers valuable insights for other mosquito control programs looking to tackle the challenge of insecticide resistance. By adopting a holistic approach that incorporates IPM principles, community-level interventions, GIS technologies, and collaboration with research institutions, NSMAD has made significant progress in addressing resistance issues and ensuring the effectiveness of their mosquito control efforts. As Dr. Clifton aptly summarizes, “Resistance management is synonymous with resistance prevention, and both are really a part of an IPM methodology. If you are really adhering to an IPM framework, then you are also doing resistance management and resistance prevention.”
As you can see, there is not just one correct answer when it comes to tackling and responding to insecticide resistance. Let the capabilities of your vector control program, your local mosquitoes, and your constituents’ needs drive your insecticide resistance management plan. Identifying the problem and taking even a small step to combat it is better than no attempt at all.
~Written by Joe Iburg
Technical Development Specialist, Azelis A&ES
Azelis A&ES 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 a manual.
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