Spotlight: Resistance Management Program at Shasta Mosquito Vector Control 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.

Resistance Management Shasta MVCD

In the western region, we interviewed Peter Bonkrude, District Manager at Shasta Mosquito Vector Control District (SMVCD). Peter has been working in the mosquito control industry since 1999. While pursuing his undergraduate degree, he worked as a seasonal mosquito technician and has since worked in various roles prior to his current role of District Manager. His program is responsible for 1,100 square miles and protecting 130,000 residents from the nuisance and public health threat of mosquitoes.

While resistance management has always been a concern at SMVCD, the increased focus and resources throughout California created an opportunity for a formal program focused on the topic. Additionally, anecdotal accounts from field staff indicated that there was decreased efficacy in some products that were being used.

Shasta MVCD logo

How it started…

Since 2010, SMVCD has been conducting ever-increasing levels of resistance monitoring and have continually strengthened the technical know-how of their team of 15 full time and 6 seasonal employees. The team takes advantage of workshops and trainings provided by AMCA, MVCAC, and the Pacific Southwest Center of Excellence in Vector-Borne Diseases (PacVec).

Shasta MVCD’s Approach to Monitoring and Managing Resistance

Shasta MVCD has a team focused on this resistance management program. The Vector Ecologist and lab staff handle mosquito rearing, laboratory assays, coordinating and assisting with field trials, and collaborating with outside research groups. The Assistant Manager and Operations Department concentrate on the field evaluations and using the resistance monitoring information to inform operational treatment decisions and implement rotational strategies.

The photo to the right shows Shasta MVCD Vector Technician, Corey Boyer, placing cages of mosquitoes in the field for a field product trial.

FIELD TRIAL

“We divide our resistance management plan into two broad categories: immature control and adult control. Our immature resistance management plan is still in its beginning stages, while our adult program is more advanced and utilized several methods for resistance surveillance and management.”

Larval Resistance Program

Currently, SMVCD’s larval program is heavily focused on field indications of resistance via the monitoring of product efficacy. Peter’s team does not just apply the product, but also monitors the longevity of the product and variables that may impact the efficacy. This is done for all products, both new and existing. Through their observations and the data collected from field samples, Peter’s team evaluates emergence inhibition and mortality for the larvicides they utilize. These field evaluations have been done for 9 different products and help inform treatment decisions. In addition to the field-based monitoring, Peter has been working to expand the larval program through larval bioassay trainings with Dr. Su at West Valley Mosquito and Vector Control and PacVec. This will improve the program’s ability to detect and respond to resistance in their area.

Adult Resistance Program

The adult resistance monitoring program features both laboratory assays and field trials. Two to three times a year, CDC bottle bioassays are conducted with products used routinely by the program. When possible, kdr mutations are also monitored to elucidate underlying resistance mechanism(s). These products are also tested using field trials late in the season. The combination of the laboratory and field data provides SMVCD with an early-warning system as well as operationally relevant efficacy data.

The picture to the right shows Shasta MVCD Vector Ecologist, John Albright, coating a bottle with insecticide in preparation for a CDC bottle bioassay.

CDC bottle bioassay

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.

VectorSurv

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:

  1. Time
  2. A limited adulticide toolbox
  3. 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:

Peter Bonkrude
resistance management

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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