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 6-9 months long; you will rotate anywhere 2 to 4 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.
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.