Combatting Mosquito Insecticide Resistance – Rotation and Integrated Mosquito Management: Southeast

The topic of insecticide resistance has received increasing amounts of attention within the operational mosquito control industry. As a result, assays are being conducted in many areas, including your region, to identify and monitor resistance so that it can be swiftly and efficaciously addressed.

Below are a couple of examples of documentation of resistance in the southeast region of the US in Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus. These studies indicate that there is resistance in all these species to multiple active ingredients.

The good news is it is not too late to act. Populations classified as ‘susceptible’ and ‘developing resistance’ are still present and now is the time to develop and implement resistance management strategies.

Facts

  1. A review of the scientific literature reveals that resistance is a widespread problem that needs to be addressed.
  2. Rotation of chemical classes (i.e. between a pyrethroid and organophosphate) is the recommended rotational strategy from the Insecticide Resistance Action Committee (IRAC).
  3. The rotation interval will depend on your local mosquito populations, and their response to various adulticides. However rotating chemical classes, when possible, on a 2-3-month schedule is our recommendation.
  4. True rotation is switching between products with different modes of action. Therefore, switching between various pyrethroid active ingredients (etofenprox, sumithrin, deltamethrin, resmethrin, prallethrin, permethrin) or combinations of these products is NOT a true rotational strategy. These active ingredients, although different, act on the same target site in the mosquito and should be rotated with active ingredients that act on a different target site.
  5. Malathion is one of the only organophosphates that can be applied by ground and should be used in rotation with pyrethroids.

Operational Recommendations

From your fleet of ground-adulticiding vehicles, set up ½ with your preferred synthetic pyrethroid product and the other ½ with Fyfanon (EW is low odor, water-based formulation; ULV is an oil-based formulation). On a 2-3-month cycle, switch the routes that spray trucks are applying. Routes that were being treated with the synthetic pyrethroid product will now be treated with Fyfanon and vice versa until your next rotation occurs. This means that if you’re mosquito season is 9-12 months long; you will rotate anywhere 3 to 6 times annually. This method also doesn’t require re-calibration. Alternatively, you can rotate your entire fleet between a pyrethroid and organophosphate every 2-3 months. Keep in mind, re-calibration will be required every time you are switching between products in your sprayers. Also, remember to start your mosquito season with a different product than you ended with in the previous year.

Fyfanon Dual Tank

The efficacy of this rotational plan should be supplemented with resistance monitoring and field validation through field trials whenever possible to ensure you are maintaining maximum efficacy.

Of course, the use of adulticides for mosquito control falls into the larger picture of integrated mosquito management. In addition to having a plan for adulticide rotation, emphasis on your larvicide program can aid in resistance management. Larvicides have a greater number of active ingredients to choose from within three classes and some even provide intrinsic resistance management, reducing the likelihood of developing resistance to larvicides. Application of larvicides and combatting mosquito populations while they are confined in a single habitat, and are not biting/flying adults, will reduce populations and alleviate the stress on adulticides (and your constituents).

Like adulticides, overuse or sublethal dosing of larvicides can cause mosquito populations to develop tolerance and eventually resistance to some active ingredients. Lysinibacillus sphaericus, Spinosad, and (S)-methoprene have all been documented in the literature to have caused resistance in populations. However, the “magic bullet,” or Bacillus thuringiensis israelensis, has been used to combat resistance to these products and eventually return mosquito populations to larvicide susceptibility. According to the EPA, there is no evidence of documented resistance to Bti in its 30+ years of use, which is likely due to the synergistic nature of the four protein toxins.

Benefits of Resistance Management

  • Rotating insecticides will delay the onset of insecticide resistance and preserve the effectiveness of your adulticides.
  • This strategy does not require mid-season recalibration.
  • Applicators can keep their original routes when the products are rotated mid-season.
  • Emphasizing all parts of integrated mosquito management ensures your program achieves the highest levels of control while preserving product chemistries.

References

Parker, C., D. Ramirez, C. Thomas, and C. R. Connelly. 2020. Baseline susceptibility status of Florida populations of Aedes aegypti (Diptera: Culicidae) and Aedes albopictus. J Med Entomol. 57(5): 1550-1559.

McInnis, S.J., J. Goddard, J.H. Deerman, T. Nations, and W.C. Varnado. 2019. Insecticide resistance testing of Culex quinquefasciatus and Aedes albopictus from Mississippi. 35(2): 147-150.

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