The Swine Health Information Center, in collaboration with the American Association of Swine Veterinarians, hosted a webinar on mosquitos and their impact on swine health and production Aug. 26. Goals of the webinar were to understand the role of mosquitos as a vector for disease transmission and to take actions to control mosquito populations near swine farms. The webinar featured four subject matter experts sharing insights on entomology and mosquito life cycles, experience on managing mosquitos in and around swine farms, and best control practices to reduce the impact of insect bites on pork production.

Presenters offering their expertise included Dustin Swanson, USDA-ARS, Bernie Gleeson, SunPork (Australia), Natalee Judson, Pipestone, and Chris Rademacher, Iowa State University. Because of this year’s widespread unusual rainfall during spring and summer, ideal conditions exist for explosive mosquito population growth. Mosquitos can transmit many pathogens and pose a risk to swine health and production.

Mosquito biology

Swanson shared information on mosquito biology, including lifecycle stages, habitats needed for growth and control strategies to reduce mosquito populations. Mosquitos have four stages starting with eggs laid in, on, or near stagnant water which then develop into an aquatic larval feeding stage. Next is an aquatic transitional pupal stage followed by the terrestrial adult stage.

The egg stage is the least noticeable to the naked eye. Eggs can be laid singly or in rafts of 80 to 100 several times over by an adult female. While eggs are typically in, on, or near standing water, Swanson stated some eggs can survive dry periods of several months and reemerge after rainfall. The second-stage aquatic larvae are worm-like and have a bulbous segment behind the head. Larvae can be found floating on water at the surface and are commonly referred to as wrigglers due to the characteristic swimming motion when disturbed. They filter feed small food items during this stage and can be a target for management strategies such as water-based insecticides

In the pupal stage, larvae go through a cocoon-like stage that is mobile. This is a water-based, non-feeding stage where pupae are comma shaped. Swanson notes at this stage, they are not a target for control strategies. Adult male and female mosquitoes are both equipped to fly and both feed on sugar sources such as flower nectar and honeydew. Swanson noted males use sugar as their sole source of nutrition and that both sexes are susceptible to targeted management efforts, such as attractive sugar baits. However, he cautioned that non-target species such as honeybees could be affected when using toxic sugar in the environment.

Mosquitos breed in stagnant water lacking an abundance of predators such as fish. This can include ponds and some streams; however, standing water resulting from human activity such as water pots, wheelbarrows and drainage runoff are common breeding sites. Mosquitos mate in swarms and Swanson explained males fly near specific landmarks waiting for females to breed. The females fly into the swarm and will typically mate with one male. Females are the only sex which consume blood meals and during the blood feeding stage, females use blood proteins to develop and hatch eggs. Each clutch of eggs typically requires a blood meal.

Mosquitos can cause harm to pigs through physical bites and blood loss but also through the transmission of pathogens during blood feeding. Blood feeding can result in stress or allergic reactions in the host, anemia, loss of productivity and reduced weight gain in livestock. For virus transmission, a mosquito must feed from a virus-infected host, then internally replicate the virus, seek a susceptible host for a blood meal, and transmit the virus through saliva to a susceptible host. Mosquitos can carry and replicate pathogens that affect multiple species including pigs. Understanding the lifecycle and biology of mosquitos assists in the targeted development of effective control strategies to reduce the negative impacts associated with mosquito bites.

2022 Australian experience

Gleeson reviewed the Australian experience during the 2022 outbreak of Japanese encephalitis virus in humans and pigs. Management strategies in Australia were built acknowledging water habitat for mosquitos will be present and wild bird populations cannot be controlled. Consequently, control efforts focused on mosquitos including emergency chemical use permits issued for control of mosquitos in standing water, in and around piggeries, and on pigs. Gleeson noted that pig skin damage from mosquito bites was not a feature of the JEV outbreak.

During the JEV outbreak, Australian stakeholders collaborated to publish a guide entitled Integrated Mosquito Management Practices for Piggeries as an aid to the industry. Gleeson encouraged producers and veterinarians to seek professional assistance when dealing with mosquito control needs. Australian efforts included medical entomologists as well as urban and peri-urban professional pest control experts.

Surveillance is a key element of integrated pest management. Gleeson stated Australian stakeholders reviewed existing surveillance and reporting systems to identify location and activity of mosquito populations. State government programs were in place and on-farm surveillance (trapping mosquitos) was initiated using CO2 and light traps. The resulting data helped direct management actions.

In Australia, applied and recommended management strategies include environmental controls of vegetation management and removal of standing water sources. Larval stage mosquito control was found to be very productive with S-methoprene and Bacillus products used in standing water. With chemical controls, Gleeson underscored the related environmental considerations including potential residues and included careful consideration of control products and application methods. In Australia, the use of direct topical application to pigs for repellant options required emergency permits and Gleeson pointed out these were a last resort, labor intensive and had withdrawal requirements which limited their use to only breeding stock.

Current U.S. experience

Judson shared her experiences within their production system from late June to early July in the Upper Midwest where mosquito season typically runs from April to October annually. Challenges were created by extensive rainfall in the spring and early summer of 2024 in Iowa and Minnesota across areas with large concentrations of pigs. The excess rainfall created an ideal environment for mosquito breeding grounds including excess fresh, waste, and stagnant standing water.

Judson noted the negative impact for swine due to increased mosquito populations, including the increased threat of viral infections from bites as well as physical blemishes on animals’ hides on-farm and at harvest sites. At harvest, 20% to 80% of loads delivered during this time period had blemishes. Additional impacts included carcass condemnation.

Judson stated the incorporation of multiple approaches targeting all stages of the mosquito life cycle is critical to reducing mosquito populations. Environmental management efforts to consider include proper site drainage, reducing standing water, maintaining well-kept premises mowed and free of weeds, ensuring effluent flows freely, turning off outdoor lights at night, and increasing airflow (cfms) to prevent mosquitos from settling. When considering chemical management, Judson mentioned pyrethrin and pyrethroid insecticides, larvicides and insect growth regulators are potential interventions targeting different lifecycle stages. IGR products are available in liquid, wettable granules and feed-through formulations. Options for adult mosquitos include spraying and fogging products.

Judson encouraged pork producers to contact their veterinarians to assess farm-specific needs related to mosquito control and management to mitigate risks of disease transmission and production losses.

On-farm mitigation

Rademacher noted the unusual rainfall amounts during spring/summer of 2024 in the Midwest resulted in increased mosquito-related producer concerns such as carcass blemishing. Red and raised lesions due to bites are associated with the stimulation of histamine release, Rademacher noted.

In response, Rademacher collaborated with industry stakeholders to assemble information for producer awareness and assist with mitigation and control of mosquitos. Stakeholder input was gathered from the AASV list serv, production systems, USDA and allied industry entomologists and tech service staff. With the input received, Rademacher and colleagues developed and published Management of Site Insect Levels to Minimize Carcass Impact, a multi-faceted approach to insect management.

Key steps for an integrated pest management approach include:

Rademacher emphasized that when considering mitigation and control strategies, especially for chemical spray utilization, it is important to review product specific withdrawal times and strictly follow regulations. Rademacher noted additional resources available for producers, including the Iowa-based mosquito surveillance that can be accessed here. Differences noted between the prevalence of mosquito populations surveyed during the 2023 dry season and the 2024 season was significant. Data includes mosquito species recently identified as well.

Changes in environmental conditions, specifically during high rainfall seasons, may result in increased mosquito populations that can lead to subsequent emergence of diseases and other challenges for swine health and production. Understanding the biology and lifecycle of mosquitos can aid in the development of mitigation and control strategies to reduce the risk of transmission of pathogens and improve swine health and welfare.