Operational Application of Resistance Management Program
With all of this information that SMVCD collects, I wanted to know how it translates operationally to Peter’s program.
“In general, we rotate between three distinct larvicide modes of action to mitigate any potential resistance: (s)-methoprene, spinosad, and microbials (Bti and Ls) … We do not currently have a strict number of applications to consider before rotation to another product, however we begin our rotation assessments at 4 consecutive applications in a single season for slow-release products (30+ days) and 10 consecutive applications of short-lived products (30 days or less) … For adult mosquito control our most widely used adulticide is permethrin-based and we apply at the higher end of the label to ensure a lethal droplet. In areas where we are heavily pressuring the populations each season, we rotate from our pyrethroid applications to an organophosphate (Fyfanon® ULV).”
And the resistance management for SMVCD doesn’t stop there! These rotational plans that have been developed are only a part of the Integrated Vector Management practices that are employed. In addition to the resistance program and operational choices outlined above, the district regularly reviews and updates their treatment thresholds, so they are both season- and species-specific. This results in the most targeted and efficient control strategies. Those control strategies are not just limited to chemical solutions, but also incorporate physical control, biocontrol, and an active outreach program.
As a result of implementing these resistance management practices Peter and his team at SMVCD have observed fewer adult mosquitoes. He said, “By rotating products and varying control strategies our immature control program continues to build in both efficacy and efficiency. For our adult resistance management plan, although we continue to see shifts in potential resistance in our local populations, we can respond to those shifts and achieve efficacious control.”
This map from VectorSurv shows resistance data from the CDC bottle bioassay. It shows the response of field populations to various active ingredients.
Challenges to Resistance Monitoring and Advice to Get Started
In Peter’s opinion, the biggest challenges to the effective implementation of a resistance management plan are:
- A limited adulticide toolbox
- External pesticide pressures on mosquito populations.
The core efforts of SMVCD are focused on surveillance and control and when resources are short, those are the objectives that get prioritized. He added that:
“With functionally two rotational products and other inputs for pesticide pressure, the move of our local populations toward higher resistance may be largely out of our control. However, by maintaining our surveillance in the areas that we make the highest proportion of our applications we can continue to stem the tide toward irreversible resistance.”
Overall, Peter believes there is an immense amount of value in monitoring for and managing resistance in local mosquito populations and believes each agency should have the ability to obtain this information, either in-house, or through a regional resistance monitoring resource.
The advice that Peter would offer to those interested in establishing a resistance management program is: