Mosquito Control After a Hurricane or Flood

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What is the difference between post-storm nuisance mosquito control and mosquito-borne disease control?

  • Adult mosquitoes do not generally survive high winds associated with a hurricane.
  • An increase in mosquito populations is expected in the weeks after flooding.
  • An increase in the number of people getting sick from diseases spread by mosquitoes, however, is not expected after flooding.
  • Flooding causes “floodwater mosquito” eggs, which were previously laid in moist soil, to hatch. The result is very large populations of floodwater mosquitoes, most of which are considered “nuisance mosquitoes.”
  • Nuisance mosquitoes do not typically spread viruses that make people sick.
  • Large numbers of nuisance mosquitoes can affect recovery efforts, and mosquito control experts often take steps to limit their numbers.
  • Rainfall can increase container-breeding mosquitoes that can spread diseases 2 weeks to 2 months after rains. Disease spread is not common after a hurricane, but is possible, especially in areas that received a lot of rainfall, but did not flood or have very high winds that would have dispersed mosquitoes and caused birds (virus reservoirs) to flee the area. So, cleaning up debris that may act as containers for mosquito breeding is still important, both from nuisance and disease points of view.

What are the goals of the DHEC Mosquito-Borne Disease Program?

  • Conduct surveillance activities that include sustaining capabilities to capture occurrences of mosquito-borne diseases, perform epidemiological investigations, and test people, mosquitoes, birds, and veterinary animals for infection with mosquito-borne diseases.
  • Provide recommendations consistent with Integrated Mosquito Management (IMM) guidance as established by the American Mosquito Control Association (AMCA).
  • Serve as ArboNet™ and MosquitoNet™ points of contact for South Carolina; enter all appropriate human and veterinary case data, as well as bird and mosquito surveillance data.
  • Provide guidance and technical support post emergency (hurricanes, tropical storms, etc.) to local government officials or local vector control agencies.

What are the limitations of the DHEC Mosquito-Borne Disease Program?

  • DHEC is not a resource for operational mosquito control supplies. We assist local programs to coordinate with external resources as needed to implement various aspects of IMM.

What will DHEC do to assist with post-storm Integrated Mosquito Management?

  • Collaborate with state emergency management, FEMA, and other agencies to provide guidance and resources to local authorities.
  • Provide technical guidance and expertise as requested by the State Emergency Operations Center.
  • Consult on specific and/or emerging issues with local programs through the State Emergency Operations Center.

What are county and municipal roles in post-storm Integrated Mosquito Management?

  • Perform mosquito trapping and landing rate counts, and track mosquito complaint calls.
  • Perform adulticiding, if deemed necessary by county or municipal officials, by using (1) county or municipal equipment and staff; (2) a Memorandum of Agreement (MOA) or Memorandum of Understanding (MOU) with a local city, county, or neighboring county/city; (3) a Statewide Mutual Aid Agreement; or (4) a mosquito control contractor acquired through a county, multi-county, or state contract or by submitting a resource request to State Emergency Management when local resources have been exhausted.

What are the eligibility requirements for Federal Emergency Management Agency (FEMA) reimbursement of mosquito control?

  • A State, Territorial, Tribal, or local government public health official validates in writing that a mosquito population poses a specific health threat. FEMA consults with the Centers for Disease Control and Prevention (CDC) to determine the eligibility of mosquito abatement activities. FEMA only provides Public Assistance (PA) funding for the increased cost of mosquito abatement (the amount that exceeds the average amount based on the last 3 years of expenses for the same period).
  • Insecticide formulations must be among those approved and registered by the U.S. Environmental Protection Agency for use in urban areas for mosquito control.
  • Insecticides must be applied according to label directions and precautions by appropriately trained and certified applicators.
  • Mosquito abatement measures must comply with all federal, state, territorial, and local laws, ordinances, and regulations concerning vector control.
  • You must be an Eligible Applicant as defined in the Public Assistance Program Policy Guide (page 9) and have the legal responsibility (page 20) to perform mosquito abatement.

What mosquito abatement measures are available?

  • Adulticiding – The ground or aerial spraying of insecticides to kill adult mosquitoes
  • Larviciding – The application of chemicals, including methoprene or Bacillus thuringiensis israelensis (Bti), by ground or air to kill mosquito larvae or pupae
  • Breeding habitat removal or alteration (source reduction) – The modification of potential breeding habitat to make it unsuitable for mosquito breeding or to facilitate larval control, including (1) draining or removing standing water in close proximity to homes, schools, sheltering facilities, and businesses; (2) increased dewatering through pumping of existing drainage systems; (3) dissemination of information (e.g., inserting flyers with residents’ water bills, public service announcements, newspaper campaigns) to direct residents to remove mosquito breeding habitats
  • For a list of complete mosquito abatement measures, consult Best Practices For Integrated Mosquito Management: A Focused Update, published by the American Mosquito Control Association (January 2017)

What are the procedures and documentation requirements for FEMA reimbursement?

  • Before spraying, collect mosquito trap data, perform landing rate counts, document mosquito complaint calls (for adulticide use), or collect mosquito larvae dip data (for larvicide use) to verify the hazard. Prioritize counties that need to be surveyed and develop a schedule for visiting them. Finalize protocols and hire or train individuals to perform mosquito trapping or landing rate counts. Start collecting data as soon as a potential threat is identified to establish a baseline data. Data are valid for a period of two weeks only.
  • At the same time or before mosquito surveys, begin drawing polygons on county maps of places that could/would be sprayed. Keep in mind you won’t be able to spray, nor should you, the entire county. Focus on populated areas. Limitations exist as to what an aircraft can do on both the upper and lower ends of treatment areas. Short, fat polygons are easier than long, skinny ones to execute by air.
  • Before spraying, contact FEMA Environmental and Historic Preservation (EHP) Point of Contact ( to identify spray exclusion areas due to wildlife refuges or the presence of endangered, threatened, or critical habitat. State and federal wildlife refuges require special permits to spray there regardless of who is paying. The federal government must comply with the Endangered Species Act (ESA). Preparing spray maps ahead of time (regardless of the surveillance data) is important in order to compare them to endangered species maps. Performing this step ahead of time will mean you can begin spraying much quicker where needed.
  • Put contingency spray contracts (aerial, ground, or both) in place so you are ready to go once the surveillance data and ESA consultations are complete.
  • Increase personal protection messaging and encourage the use of insect repellents.
  • Validate in writing that a mosquito population poses a serious health threat or a mosquito nuisance that is severely hampering the recovery effort. Scientifically-backed details about specific areas that have been impacted by the disaster must be described; a general statement about county-wide flooding and mosquito problems will not suffice.
  • Follow the manufacturer’s label on EPA-approved chemicals for mosquito abatement by certified employees. The pesticide also must be registered in SC by the Clemson University Department of Pesticide Regulation.
  • For aerial spraying, consult the Clemson University Department of Pesticide Regulation to make sure the plane and pilot are in compliance with all applicable rules and regulations of the South Carolina Pesticide Control Act.
  • Provide documentation of the chemical, application method, and concentration used.
  • Provide adulticide or larvicide area maps detailing the zones affected/treated.
  • Provide date(s) of the insecticide application.

What types of requests for mosquito control services are more likely to get approved?

  • If a jurisdiction does not have a mosquito control program, then pre-storm mosquito data are important, although these data are not expected to exist. The jurisdiction must validate mosquito control measures by monitoring the mosquito population before and after treatment, by using landing rate counts, counting numbers of mosquitoes from traps, or documenting the number and origin of mosquito complaint calls.
  • If a jurisdiction does have a mosquito control program, then pre-storm data (3-year average) are important during the summer when mosquito numbers are high anyway, but are not as important during the fall when mosquito numbers should be dwindling.

Who do I contact for vector control resources and mosquito surveillance and control methods?

Additional Information