The District utilizes Integrated Pest Management (IPM) principles throughout its weed & pest programs for the effective, long-term, and ecologically-sensitive management of target species. These methods utilize multiple different tools including biological, cultural, physical, and chemical control, often synergistically, to achieve the most effective & beneficial outcome for environmental and human health.
A branch of IPM exists specifically for mosquitoes & disease prevention, called Integrated Mosquito Management (IMM). IMM includes a few additional tools, including disease surveillance and insecticide resistance monitoring. IMM is endorsed by the American Mosquito Control Association (AMCA), the Centers for Disease Control and Prevention (CDC), and the Environmental Protection Agency (EPA).
Why is Mosquito Management Important?
Mosquito management mitigates the risk of disease to humans by interrupting mosquito-borne disease transmission cycles and protects communities from adverse mosquito activity.
Teton County Weed & Pest District uses scientific, ecologically-sensitive, and data-driven methods to reduce public health threats posed by vector mosquitoes. A vector is any animal that is capable of transmitting a pathogen to humans that could result in disease. Mosquitoes, ticks, and fleas are examples of vectors in Wyoming.
Complete elimination of any vector is neither feasible nor the goal of our program. Rather, our mosquito program focuses on protecting both ecological and human health through best management practices that aim to strike a balance between economic, environmental, and human needs.
Integrated Mosquito Management Elements
What is surveillance?
Surveillance of local mosquito populations and the diseases they carry is the first line of defense in any integrated mosquito management program. It is essential regardless of the risk of disease outbreak. Surveillance is a type of data collection. Data collected includes where and when the mosquitoes occur, how many there are, what species are present, environmental factors, what habitats they are using, and if they are infected with viruses that can be transmitted to humans.
This data helps the District determine where and when interventions are needed, and which management response is most appropriate. Interventions are always based on "action thresholds," or surveillance data that triggers a management action from the District. Action thresholds are based on multiple pieces of information, such as mosquito abundance, virus activity, landowner permission, and weather.
The information collected also informs the District about changes in vector mosquito populations over time, the level of mosquito-borne disease risk, which species are problematic, and the introduction of any invasive or exotic mosquito species. Surveillance data is also used to evaluate our control efforts.
Mosquitoes are attracted to the carbon dioxide in your breath.
How do we survey for mosquitoes?
We conduct surveillance throughout the spring and summer by going into mosquito habitats where we have landowner permission to search for and collect live mosquitoes, either as eggs, immatures, or adults. To learn more about the different mosquito life stages, see the Mosquito Biology page.
We use various pieces of equipment to collect live mosquitoes. Most commonly used are dippers for samples of immature mosquitoes, and CDC CO2-baited light traps for adults. Once in our lab, we inspect these samples to determine the species as well as other characteristics. If any vector species are detected, they are separated for virus testing.
Mosquito Virus Testing
We use real-time polymerase chain reaction (qPCR) methods in our Biological Safety Level 2 lab to test vector mosquitoes within 24-48 hours of collection for West Nile virus, Western Equine Encephalitis virus, and St. Louis Encephalitis virus. Positive test results prompt the District to intensify and focus surveillance and control efforts in areas where virus activity was detected. Test results are submitted to the Wyoming Department of Health. Click here to view statewide WNV reporting data.
The District also tests dead birds for the presence of these viruses, which helps us determine the level of virus activity in the environment.
WNV is a zoonotic disease, meaning animals are involved in the transmission cycle. In this case, birds are the hosts of the virus in the environment. Some bird species are very susceptible to the virus and will die after infection, while others can live with the virus. Dead birds are often an early indicator of West Nile virus activity in an area. The District can test intact birds that have died within 48 hours for viruses such as West Nile virus. This information helps us monitor virus activity and focus surveillance and control efforts.
Birds can get sick and die from things like Salmonellosis as well, which can also make humans sick. Take precautions to never touch a dead bird with bare hands if attempting to move it, but rather, use gloves or an inverted bag over the hand. Wash the hands thoroughly afterwards. To report a dead bird, fill out this service request. The District will pick up and test the bird if it meets the testing criteria. Any wild bird can be reported and tested.
Mosquito Management Methods
Physical control, also referred to as larval source reduction, permanent control, habitat or environmental manipulation, is often considered the single most effective means of mosquito control. Water is required for all immature mosquitoes to complete their life cycle, and this biological characteristic can be used to target mosquito problems at the source. By removing breeding sites altogether or altering habitats so they are unfavorable to mosquitoes or promote natural predation, effective mosquito control can be achieved without the need for insecticide use. Physical control is not only highly effective, but also has economic benefits by reducing resource use.
Compared to flooded meadows and fields in Teton County, ponds are not a major source of nuisance mosquitoes. Ponds can, however, breed more vector mosquitoes.
Mosquito prevention is a shared responsibility and physical control is a large part of that. It is important that residents in Teton County help their community by reducing mosquito breeding on their properties. This is because mosquitoes are not only a nuisance, but they can transmit viruses that can make people and animals sick. Physical control also helps reduce the risk of insecticide-resistance development by limiting the pressure on insecticide use.
Physical mosquito control interventions can range from simple, including removing water-holding containers around the home, to complex such as extensive drainage practices to reduce stagnant water. Physical control methods vary based on the different mosquito habitat types.
See below the Resident's Guide to Prevent Mosquito Breeding and the Neighborhood Advocate program to learn how to reduce or eliminate mosquito breeding sources on your property and in your community.
Resident's Guide to Prevent Mosquito Breeding
Biological control, or biocontrol, is a method of controlling pestiferous organisms, such as insects and weeds, using other organisms. Biocontrol agents for mosquitoes include vertebrates, invertebrates, and microorganisms. Examples of each include predatory fish, predatory and parasitic aquatic invertebrates, and mosquito pathogens, respectively. In Teton County, the only area appropriate method currently available is the use of mosquito pathogens.
Many mosquito pathogens are very effective at killing mosquito larvae. Examples of bacteria that are pathogenic to mosquito larvae include Bacillus thuringiensis israelensis (Bti), Bacillus sphaericus (Bs), and Saccaropolyspora spinosa (spinosad). The District is currently using Bti and Bs, both of which contain toxin-producing spores. At the rate and locations the District applies Bti and Bs, these toxins can only affect mosquito larvae and do not impact other aquatic life. All of these bacteria are naturally occurring soil organisms that have been commercially produced for mosquito management. They are often referred to as biorational products, biological larvicides, or biopesticides.
The District applies Bti biological control products as either liquid or granular formulations. Applications are made using a backpack sprayer, by hand, or by drone.
Chemical control in integrated mosquito management refers to the use of specific compounds called insecticides to control either immature or adult mosquitoes. Larvicides are products used to control mosquito larvae, and adulticides are for the control of mosquito adults. The District only applies larvicide and adulticide products that are registered by the United States Environmental Protection Agency. Applications are always performed by trained applicators that are licensed through the Wyoming Department of Agriculture.
The foundation of the District’s integrated mosquito management program is prevention. Prevention is largely focused on targeting mosquito larvae using environmentally compatible larvicides to avoid the emergence of biting adults, as well as relying on the community to prevent or reduce mosquito breeding on their properties. Mosquito prevention is a shared responsibility throughout a community. This helps both the District and the community minimize the need for adulticides.
It is not always possible, however, to prevent mosquitoes from emerging. The District may apply adulticides in areas where our surveillance data indicates that West Nile virus activity poses a risk to public health or high numbers of nuisance mosquitoes exceed our action thresholds.
The types of larvicides used by the District for larval control include biorationals (see Biological Control), insect growth regulators (IGRs), and mineral oils. Depending on the size of the larval habitat, the District applies larvicide products either by hand, with a backpack sprayer, or by drone. These products are applied either as liquid or solid granular forms depending on environmental characteristics.
Insect Growth Regulators
The insect growth regulator used is called methoprene, which mimics a hormone naturally occuring in mosquito larvae. In order to transition to the pupal stage, late stage larvae must stop producing this hormone. When methoprene is applied in mosquito larval habitats, it prevents the larvae from successfully pupating and maturing into adults, ultimately causing mortality. Methoprene is specific to mosquito larvae, meaning it only works on mosquitoes and does not impact other insects. To learn about the different mosquito life stages, view the Mosquito Biology page.
Mineral oils, also called monomolecular films, are used by the District to control late-stage larvae and pupae. This is because by these stages, Bti, Bs, and methoprene are no longer effective. Mineral oil products are applied to the surface of standing water where immature mosquitoes are present. It creates a very thin layer at the water’s surface that disrupts the ability of the larvae or pupae to open their breathing tubes (siphons), ultimately causing them to drown.
Adulticides are products that reduce adult mosquito populations. The District applies adulticides using a method called truck-mounted ultra-low volume (ULV) spraying. A very low concentration of product, between ½ to 2 ounces per acre, is atomized into extremely small droplets and broadcast from the back of a truck as a fine mist that drifts along air currents. Think of a golf ball worth of very low concentration product spread out over an entire football field. In order to protect pollinators, the District only applies adulticides at dusk, when mosquitoes are most active and pollinators are inactive.
The adulticide products used by the District pose very little risk to humans, pets, or the environment. The most common type of adulticides used in mosquito control are pyrethrins. Pyrethrin is a naturally-occurring substance harvested from chrysanthemum flowers. There are synthetic forms of pyrethrins that are also commonly used, called pyrethroids. Pyrethrins and pyrethroids are in the same class of compounds as many flea and tick medications for pets, as well as head lice shampoos for children.
The adulticide products used by the District are easily biodegradable and do not persist in the environment.
Once the mist is dispersed, the products are only able to kill mosquitoes on contact for approximately 15 minutes before beginning to break down. The District uses products with very short efficacy windows to rapidly reduce adult mosquitoes in an area that may may pose a public health threat or be causing adverse nuisance problems, while limiting risk to non-target insects. By selecting adulticide products without residual activity, the District is also aiming to reduce the risk of insecticide resistance development. ULV treatments are always done in conjunction with intensified efforts to locate and reduce mosquito breeding sites to prevent more adults from emerging.
Insecticide Efficacy & Resistance Monitoring
One very important aspect of Integrated Mosquito Management (IMM) is monitoring for insecticide resistance in mosquito populations. Resistance to insecticides is caused by genetically heritable traits (something that can be passed down from parent to offspring). Resistant traits prevent insecticides from causing mortality in certain individuals within a mosquito population. If enough mosquitoes develop these traits and can survive exposure to insecticides, failure to control entire populations in the field can occur.
Because mosquito populations can transmit viruses to humans, it is important that the insecticides available to control mosquitoes remain effective. The District conducts routine tests on the local mosquito populations to monitor for any insecticide resistance development. After resistance is detected through simple routine tests, further research is conducted to determine more detailed information needed to inform resistance management decisions.
The District also monitors for insecticide efficacy, or that insecticide applications were made successfully. Factors impacting the efficacy of insecticide applications may include variations with weather, irrigation patterns, and equipment for example. This helps inform the District that applications are being made effectively and if any changes in management practices are needed.