Spotlight: Resistance Management Program at Chesapeake Mosquito Control Commission

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.

In the northeast region, we interviewed Lisa Wagenbrenner, Director at Chesapeake Mosquito Control Commission (CMCC). Lisa started off in mosquito control as a seasonal mosquito intern for the City of Virginia Beach, while finishing her degree in Biology. In 2006, she was hired as the Biologist for the City of Hampton and then in 2009 was hired as the Head Biologist for CMCC. Lisa shares, “I have been a mosquito nerd for 19 years!” From 1948 to 1965, five independent mosquito control districts were created in what is now the City of Chesapeake, Virginia. Each of the five commissions operated independently and were individually funded by special taxes levied specifically for mosquito control. In 2003, the five mosquito control commissions consolidated to become Chesapeake Mosquito Control Commission with three districts to cover the entire city.

Chesapeake Mosquito Control Commission

Chesapeake’s program is now responsible for 353 square miles and protects 246,000 citizens (2nd largest population in Virginia), within Southern Chesapeake, Greenbrier and Deep Creek, from the nuisance and public health threat of mosquitoes. Chesapeake has an abundance of diverse mosquito habitats, which range from urban container mosquitoes to open farmland, marshes, and the Great Dismal Swamp where pesticide usage is restricted.

“[Insecticide resistance monitoring] contributes to our efficiency, and our bottom line, and allows us to be environmentally sound without compromising service to our citizens. We can control mosquitoes and reduce the likelihood of the transmission of mosquito-borne diseases to humans and horses in the most economical responsible way.”

CMCC’s Approach to Monitoring and Managing Resistance

CMCC’s Biology Department is responsible for planning, running, and record keeping of the cage field trials, bottle bioassays, and larvicide efficacy/resistance trials. Their Physical Assets Manager is responsible for upkeep of our large assortment of pesticides and guides the supervisors on the best products to use. Lisa states, “We are constantly training our field techs on all our products, the “What, When, Where” concept.”

“We have always had a resistance management plan in place by following our philosophy of integrated pest management (IPM). Using IPM with various methods and materials accomplishes many goals:

1.  It acknowledges that mosquito species differ and require different monitoring and control techniques.
2.  It emphasizes source reduction- a longer term strategy and does not involve pesticides. This involves public education about artificial containers to the drainage maintenance program.
3.  It increases the types of both natural and synthetic pesticides used to reduce the possibility of pesticide resistance.
4.  It places priority on controlling immature stages to reduce mosquito numbers before they become adults.
5.  It is the safest system for humans and the environment and has the biggest impact on the target species.
6.  It saves money by making pesticide applications dependent on surveillance data, rather than on a set schedule.

Our budget has allowed for us to acquire a diverse inventory of both adulticides and larvicides giving us the ability to rotate products over the years.”

When asked what changes have been observed over the years in their operations due to their resistance plan, Lisa shares, “We have the ability to reduce problem species of mosquitoes when they arise and a better understanding of our pesticides allowing us to react quickly and plan for the future. Our larviciding program is enhanced by the knowledge acquired from our trials. We know the best product to use in any one of our many diverse mosquito habitats.”

At the beginning of their resistance program, Chesapeake relied on supplies and training from external sources (CDC, NEVBD-Cornell, various vendors), they now have a dedicated budget line for educational supplies that includes door tags and mosquito information brochures. Fifteen years ago, Chesapeake was awarded an educational grant that was instrumental in the development of their 3rd grade outreach program that is still in place today, which helps to promote source reduction.

Adult Resistance Program

CMCC prevents resistance by rotating products and monitoring efficacy by using cage field trials and bottle bioassays. Lisa shares, “Some of our early cage field trials were conducted with the assistance from our pesticide vendors. Three years ago, the CDC began an extensive program of bottle bioassays funded by leftover funds from Zika research.  The technical grade pesticides are sent free of charge along with the supplies to run bottle assays.” In fact, the CDC is still providing bottle bioassay kits free of charge to anyone in the country.

Larvicide Resistance Program

The Northeast Regional Center for Excellence in Vector-Borne Diseases- Cornell has been assisting Chesapeake’s program by providing free materials for larvicide resistance testing for both (S)- methoprene & Bti on Ae. albopictus and Cx. pipiens. Lisa states, “Due to time constraints we have not taken advantage of this program as of yet.” However, just two years ago, they designed their very own in-house larvicide efficacy/resistance program by building pools to resemble or mimic a field application (49 sq. ft and 100sq. ft).

chesapeake mosquito control

Operational Application of Resistance Management Program

With the various resistance management techniques that CMCC uses, I wanted to understand how it translates into operational use in Lisa’s program. “A few years ago, we implemented cage field trials, bottle bioassays and efficacy trials with larvicides. As more information was disseminated from the CDC on pesticide resistance showing up in many parts of the country, we saw a need to add to our IPM program. We also implemented trap-spray-trap on a few occasions when we were crunched for time and needed information quickly on the effectiveness of our adulticides on specific target species. We now have a better understanding of which products are more effective. Our current adulticide inventory consists of deltamethrin, etofenprox, malathion, permethrin and resmethrin. Our rotation involves spraying the most effective product in specific areas where the target species is problematic.

We continue to gather information on our newly formed larvicide efficacy program, including how specific target species react to certain larvicides. We can adjust our output (lower or higher) depending on the species and environmental conditions. Our current larvicide inventory consists of a variety of formulations of (S)-methoprene, Bacillus sphaericus, Bacillus thuringiensis israelensis, various oils and a monomolecular film. As you can see, our budget has allowed us to obtain many different products over the years. I believe this has reduced our potential for resistance build up.”

Challenges to Resistance Monitoring and Advice to Get Started

In Lisa’s opinion, the biggest hurdle in their resistance management plan is the limitations of staff or pesticide inventory. She states, “If you don’t have enough people or a limited pesticide inventory it’s difficult to run trials and rotate products, but there are ways to accomplish a plan with determination.  You must work with what you have. Just because your district is small does not mean you can’t implement all aspects of a good IPM/resistance program. “

When asked if it is beneficial for a vector control program to have a dedicated resistance management plan, Lisa shares, “Absolutely! We all share the same common goals in mosquito control: reduce nuisance mosquitoes and control the spread of mosquito-borne diseases. The more knowledge we can gain on the best products to use in our respective areas, the better we can control mosquitoes.”

The advice that Lisa would offer to those interested in establishing a resistance management program is, “If working with a limited budget, start off small. Take each factor of a good IPM plan and decide which one is the weakest and build on it. Reach out to neighboring mosquito control programs for advice and insight on the products they find effective or not. The base for any management program is a strong surveillance team, you can’t apply pesticides correctly or efficiently without knowing the species you are dealing with. Next, train, train, train! I can’t emphasize enough how important it is to have an educated field crew on the importance of applying the correct amount of pesticide and the local mosquito species. Under-applying is just as bad as over-applying and can lead to resistance in the local mosquito population. Also, educating the citizens during service calls can help reduce the ever-challenging control of container mosquitoes and the need for adulticiding at every residence.”

mosquito resistance

As you can see, there is not one simple 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 small steps to combat resistance is better than no attempt at all.

~Written by Emily Boothe
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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