An Introduction to the Mosquitoes of Michigan :
Their Biology & Control

Mosquitoes are by far the most dangerous animals on earth. It is hard to comprehend the amount of disease and the resulting sickness, death, and economic loss caused by the mosquito. Some scientists estimate between 500 and 700 million people get malaria worldwide each year. That’s more than twice the entire population of the United States each year.  Malaria has since been virtually eliminated here in Michigan , but the threat of mosquito-borne disease is still very real.  Of the 60 different species of mosquitoes found in Michigan many are known to be vectors (carriers or transporters) of important diseases such as West Nile virus, Eastern Equine Encephalitis, St. Louis Encephalitis, and the California Group of encephalitis.  Mosquitoes are the most medically important insects in Michigan and the entire world, thus it is imperative that pest management professionals understand mosquito biology and control.

The all too familiar mosquito nuisance also threatens our health.  Health can be thought of as a “state of well being.”  A person who is pestered and bitten by mosquitoes has an impaired state of health.  Individuals and their families are often kept from outdoor recreation and activities due to nuisance mosquito populations.  The bite or multiple bites resulting from mosquitoes can cause varying levels of discomfort from a slight itch to a severe allergic reaction.  Mosquito control has an important role in maintaining public health even in the absence of disease transmission.

MOSQUITO BIOLOGY. Mosquitoes, like other flies, undergo complete metamorphosis, having egg, larval, pupal and adult stages. Larvae are commonly referred to as "wigglers" and pupae as "tumblers." Larvae and pupae of mosquitoes are always found in water. The breeding source may be anything from water in discarded tires to water collected in plants, to pools, puddles, and swamps. Mosquito species differ in their breeding habits, biting behavior, flight range, etc. However, a generalized description of their life cycle is presented here and will serve as a useful basis for understanding mosquito biology and ecology. Most larvae in the subfamily Culicinae hang down just under the water surface by a breathing tube (siphon), whereas anopheline larvae lie horizontally just beneath the water surface supported by small notched organs of the thorax and clusters of float hairs along the abdomen. They have no prominent siphon. Mosquito larvae feed on suspended particles in the water as well as microorganisms. The mosquito larva has 4 instars (stages) and undergoes four molts (each successively larger), the last of which results in the pupal stage. Mosquito pupae do not feed and will "tumble" toward the bottom of their water source upon disturbance.  They emerge as adult mosquitoes in two to four days.  With optimum food and temperature conditions, the time required for larval development can be as short as seven days.  When the adult is ready to emerge the pupal skin splits from the top, and the adult slowly emerges onto the water surface.  The adult will remain on the water surface until its wings harden.

Adult mosquitoes of both sexes obtain nourishment for basic metabolism and flight by feeding on plant juices and nectar from flowers. The female mosquito is solely responsible for biting; the females of most species require a blood meal for egg development.  They not only bite people, but also obtain blood from birds, mammals, reptiles or amphibians. 

Michigan has three major classes of mosquitoes based on larval habitats (breeding sites) and life history:  permanent water mosquitoes, floodwater mosquitoes, and artificial container/tree hole mosquitoes.  These are general categories and some species may be found in more than one type of habitat, for example Culex pipiens larvae may be found in permanent water habitats (sewage lagoons), but may also be found in artificial containers (tires); the shared appeal is foul, polluted water. 

Permanent water mosquitoes in Michigan, which include Anopheles and many Culex species, and the unique Coquillettidia perturbans, can be found in various permanent habitats, such as swamps, ponds, sewage ponds/lagoons, and ditches that do not usually dry up.  These permanent water mosquitoes can be subdivided by the quality of water.  Cq. perturbans and Anopheles, which include An. quadrimaculatus and An. perplexens, prefer clean or relatively unpolluted water, as found in swamps, ponds, and large ditches.  Culex mosquitoes, primarily Cx. pipiens and Cx. restuans, prefer polluted/highly organic water, as is often found in sewage lagoons and catch basins.  Anopheles and Culex females lay their eggs directly on the water surface, Anopheles individually and Culex in groups of attached eggs called rafts.  These two groups are capable of many generations per year and typically over winter as mated females.  The Cq. perturbans is unique in that it is found in freshwater habitats that possess emergent vegetation.  Both larvae and pupae possess a modified tube adapted to pierce and attach to the submerged roots and stems of aquatic plants for the purpose of obtaining oxygen.  The adult female lays its eggs in rafts directly on the water surface.  Cq. perturbans only has one generation a year (takes a year to go through its life cycle) and over winters in the larval stage.

Floodwater mosquitoes are found in habitats that are temporarily flooded for a portion or for brief periods throughout the year.  The mosquitoes’ ability to utilize these short-term breeding sites lies in their desiccation-resistant eggs.  The eggs are laid in ground depressions which flood when conditions are right; this often occurs in the spring after snow melt and after summer storms.  Eggs can remain viable up to 7 years after being laid.  There are two groups of flood water mosquitoes, the spring floodwater mosquitoes and the summer floodwater mosquitoes. 

Larvae of spring floodwater mosquitoes hatch from the eggs in late March, in pools of water formed by melted snow in the woods.  The eggs occur in the leaf litter at the bottom of the pools. These larvae develop slowly because of low water temperatures, and emerge as adults in May, before the pools dry up.  The female spring floodwater mosquitoes can be very long-lived, and may bite several times.  They lay eggs in the woods where they will be flooded the following year.  Spring floodwater mosquitoes have only one generation per year, so even if these eggs are flooded by summer rains, they will not hatch until the following spring.  The species names of some spring floodwater mosquitoes are:  Ochlerotatus stimulans, Ochlerotatus excrucians, Ochlerotatus provocans, and Ochlerotatus canadensis.  There are several other species as well, but they all have the same type of life history pattern.

Summer floodwater mosquitoes include several of our most common pest mosquitoes in Michigan , such as Aedes vexans, Ochlerotatus trivittatus, and Ochlerotatus sticticus.  Larvae hatch from eggs after rainfall in the summer (usually 1 inch or greater) in shallow flooded areas such as meadows, floodplains, roadside ditches, highway right-of-ways, tire tracks, cow hoof prints.  The larvae develop very quickly (7-10 days) and several generations may occur each summer depending upon the frequency and intensity of rainfall.  For any given summer, it is hard to predict in advance how bad the summer mosquitoes will be, because it’s difficult to predict rainfall.

Artificial container/ tree hole mosquitoes not only make use of natural tree holes but also breed in discarded tires, rain buckets, or anything that may hold water.  The most common species in Michigan is the native Ochlerotatus triseriatus and the new exotic Ochlerotatus japonicus.  The eggs are often laid on the walls of the containers just above the water-line.  When the next rain event occurs the eggs become submerged and hatch shortly thereafter.  These species are capable of many generations per season.  One may also find that several Anopheles and Culex species may occasionally lay their eggs in these habitats.  The type of species found in the container is often dictated by the location and water quality of the container.  Oc. triseriatus and Oc. japonicus will often be found in wooded habitats, whereas Cx. pipiens will often be present in those containers with rather organic water located in an open yard setting.

DISEASES.  Many of the above mosquito species are very important disease vectors for many different arboviruses (arthropod-borne virus) here in Michigan .  These viruses are cycled by many different mosquito species within various Michigan bird and mammal populations.  Mosquito-borne encephalitis is not common annually, but because it may occur in epidemics and localized areas in certain years, it remains a true concern for human and animal health.  West Nile virus (WNV) has been the most notable as of late and is responsible for hundreds of deaths and thousands of sicknesses in the United States , since it was first detected in 1999.  Dog heartworm is common in Michigan and is transmitted by a variety of Ochlerotatus and Aedes mosquitoes. Prophylactic drugs are available from veterinarians to prevent dogs from contracting this disease. St. Louis encephalitis (SLE), eastern equine encephalitis (EEE), and different types of the California group of encephalitis also occur in Michigan on occasion. 

As mosquito control personnel, it is important to monitor and respond to disease threats.   Disease surveillance, such as mosquito sampling, wild and sentinel bird sampling, and monitoring dead bird reports, is invaluable to mosquito control programs.  Programs that incorporate one or more surveillance tool will be most effective in disease prevention.  Early detection and control strategies can greatly reduce the arbovirus infection risk to humans and animals.  Early detection concentrates resources and control measures to best address the disease threat.  Control measures taken early in a disease threat will be less costly with respect to human health and economic cost than a potential epidemic.

West Nile virus in Michigan was first detected in bird populations in 2001.  It has since been responsible for many human deaths (51 in 2002), and approximately 20-40 cases of human infection a year since 2002.  WNV has also been responsible for a large number of deaths in horses.  Michigan ’s main WNV vector is Cx. pipiens; however other species may be important.  Birds are the primary reservoirs and amplifying hosts for this disease.  Several species of Culex and Ochlerotatus have been found positive for WNV in nature.  These mosquitoes likely serve as important vectors within bird populations as well as bridge vectors in human and horse infections.  Certain species of birds, especially the Corvids (crows, ravens, and blue jays) are highly susceptible to infection and are useful as wild sentinels for West Nile virus surveillance.

St. Louis encephalitis is caused by a virus that has a "natural" transmission cycle involving several species of wild birds and mosquitoes.  Cx. pipiens is believed to be Michigan ’s main vector in birds and bridge vector in humans.  Epidemics have produced human fatality rates of 4 to 20 percent with most deaths occurring in people over 50 years of age.  In 1975 an epidemic of SLE resulted in 1,967 confirmed or probable human cases and 4 deaths here in Michigan .

Eastern equine encephalitis, like SLE has a natural transmission cycle involving different species of wild birds and mosquitoes.   In Michigan , Cq. perturbans is the main bridge vector responsible for human and horse infections.  The EEE fatality rate ranges from 50 to 70 percent in humans and in horses, 90 to 95 percent.  Unlike SLE, EEE may produce severe disease and deaths in some exotic bird species like the pheasant.  The first known Michigan resident to die of EEE was a 10-year old boy in 1980.  The most recent fatal case involved the death of a teenager in Livingston County in 2001.  In 2005, the first reported cases of EEE in whitetail deer were found in both Kent County and Montcalm County .

The status of the California group of encephalitis viruses, another group of mosquito borne viruses, is less well known in Michigan compared to other nearby states.  Jamestown Canyon virus is one of these viruses.  It is widespread in distribution and is mainly transmitted by spring Ochlerotatus mosquitoes with whitetail deer as the vertebrate host of the virus.  However, it is not a major cause of human illness and does not affect domestic animals.  LaCrosse encephalitis virus, another California group virus, occurs in Michigan and is transmitted by Aedes triseriatus mosquitoes.  LaCrosse encephalitis is a serious disease of children, but is not common in Michigan .

MOSQUITO SURVEILLANCE. Routine mosquito surveillance is essential for the planning, operation, and evaluation of any effective mosquito control program.  All control decisions should be based on as much science as possible.  Surveillance will ensure the timing and choice of all mosquito control activities will have a scientific basis.  Mosquito surveillance programs will provide a listing of local mosquitoes and the effectiveness of control strategies.  Routine surveillance yields the location of breeding habitat and identification of problem sites where control should be concentrated.  Survey data will provide vital information, such as: an increase in adult numbers within an area suggesting a need for or increased control; a dominance of one species may indicate missed breeding habitat that can be investigated; or timing treatment to catch the most number of larvae and adults within a given breeding habitat or location.  Surveillance will also detect disease activity, allowing for control measures prior to an epidemic.

Mosquito Surveillance provides:

1. Listing of mosquito species within a local area
2. Estimate of adult and larval mosquito populations
3. Insight into mosquito breeding habitat
4. Locals where control efforts are needed
5. Source of female mosquitoes for disease surveillance
6. Disease activity in birds

Mosquito egg surveys utilize an oviposition jar, a black container with a suitable substrate (paper or wood) for female mosquitoes to lay their eggs.  The ovitrap is useful for collecting information on container breeding mosquitoes.  Counting the number of eggs on the substrate can estimate the number of container mosquitoes that may hatch following the next rain, as well as the number of adult females present within the sampling area.

Larval surveys provide insight into larval mosquito population densities and effectiveness of prior larval control efforts.  A white plastic dipper is all that is needed to collect water from small containers to large swamps.  Estimates of larval density can be carried out by counting the number of mosquito larvae per dip, using a standard 1-pint dipper.  A minimum of three to five dips should be completed at each site.  Large habitats, such as a farm pond, may require three to five dips at different points around or within the habitat to best represent the resident mosquito population. The number of dips and the number of larvae per dip, along with larval stage (instar) information will give control personnel an educated guess as to emergence time and what control effort(s) to use.  Some larval habitat cannot be sampled using a standard dipper; soup ladles, turkey basters, large syringes, and manual siphon pumps can be used to collect larvae from hard to sample habitat, such as tree holes, tires, and crevices.

 Adult surveys are important to surveillance programs in part as they measure a program’s success, often measuring larviciding success or a need for additional adult control efforts.   Adult surveys will also yield information as to type of mosquito habitat within and around the surveillance area.  No program will be totally successful in eradicating all mosquitoes.  The goal should be to reduce nuisance mosquitoes and mosquito-borne disease threats to an acceptable level.

New Jersey Light Traps (NJLT) stationed at fixed locations provide mosquito personnel with valuable information about adult mosquito populations.  The trap uses a 25 Watt light bulb to attract mosquitoes.  The trap is limited in location in that it uses 110 Volt AC.  Private citizens, especially retirees, living in mosquito-prone areas welcome the stationary traps and the involvement in a successful program.

CDC Traps can be used in a variety of ways to sample different species of adult mosquitoes.  The Centers for Disease Control and Prevention (CDC) has developed a portable trap that runs off a 6-volt battery or 4 “D” cell batteries.  The commonly used CDC trap is fitted with a light source or CO₂ source, or both located at the top of the trap to attract adult mosquitoes.  As the mosquitoes approach the trap, a small fan draws them into a net which is located at the bottom of the trap.  Many mosquitoes are active during the evening and into the night so CDC traps are most often deployed at dusk and picked-up after dawn.

Gravid Traps, like oviposition, jars use a dark container (plastic tray) with an organic-water mixture as the attractant.  They are lightweight and portable and powered by a 6-volt battery.  A fan housed above the water draws the gravid females into a box or net.  These traps are very important to a mosquito control program’s disease surveillance in that they collect gravid females (blood fed females ready to lay eggs). Highly organic water used as the attractant will predominately catch Culex species, which are important vectors of WNV and SLE.

Daytime resting stations are used by adults of many species of mosquitoes; houses, barns, bridges, catch basins, foliage, and many other natural and artificial shelters may be used by daytime resting mosquitoes.  Resting stations may be visited by investigators to estimate population density.  The adult mosquitoes can be sampled using an aspirator, a device that sucks insects into a collection tube or jar.  Artificial resting stations such as a wooden box or large peat pot can be used to sample an area.  Installing artificial resting stations and visiting them periodically gathers information on mosquitoes that are not usually found by other surveillance and collection efforts.

Citizen calls provide a valuable service in informing mosquito personnel of nuisance mosquito populations.  They provide information on probable habitat and future areas to target for control.  Confirming the reported mosquito problem and addressing it will not only alleviate that citizen’s problem, but other residents within the area as well; treating a small area can benefit a larger area by addressing the source of mosquitoes.

Habitat mapping and record keeping of mosquito habitat location and application methods are invaluable to mosquito control programs.  All mosquito habitats within a given area should be mapped; this is best done by foot, but often aerial photos, government drain maps, and other sources can be utilized.  Inspecting by foot will visually confirm mosquito breeding habitat.  Records of visits to these mapped sites for treatment or surveillance should be kept, noting presence of mosquitoes and changes in the habitat.  Keeping records of habitat quality and where control is needed or taken place will help ensure an effective and efficient control program.

MOSQUITO CONTROL.  Any type of control should involve careful consideration of the biology of the mosquitoes and be based on scientific surveillance.  A response to control nuisance mosquitoes may look very different from a response to control disease-vectoring mosquitoes.  In all cases, larval mosquito control should be considered as the first option for abatement. This involves location of larval habitats, followed by their modification or treatment in such a way that the integrity of the habitat is preserved but the mosquito larvae are reduced in numbers.  By controlling larval mosquitoes, the adults may never become a problem.  Larviciding has the greatest control impact on mosquito populations because the larvae are concentrated, immobile, and accessible.

The larval habitats of spring and summer floodwater mosquitoes can be permanently eliminated through environmental sanitation and civil engineering, and should be the first thing to consider for mosquito control.  Because of the temporary nature and small size of mosquito floodwater habitats, they often can be altered to prevent mosquito production.  However, there are laws and policies regulating alterations of wetlands, and the Michigan Department of Environmental Quality, Land and Water Management Division must be consulted before these activities take place.  Indeed, professionals responsible for mosquito control are in the unique position of finding a balance between preservation of our wetlands and elimination of mosquito sources, but this balance can often be achieved with the careful planning and consultation with authorities.  Landscape planners should consider carefully the kinds of mosquito habitats they may be creating when wetlands are integrated into landscape or neighborhood designs.  However, it is entirely possible to reduce larval mosquito sources and at the same time preserve wetlands and other desirable habitats.

 Source reduction of larval mosquitoes may involve: (1) installation of catchments; (2) installation of tile leading to a catchment or drain; (3) modification of grade to permit drainage; or (4) conversion of a mosquito-producing area to a non-mosquito-producing body of water such as an ornamental pond, water hazard, or permanent wetland.  For tiling purposes, "sock" tile, which allows water entry but prevents roots and debris from clogging the tile, is very useful when dealing with woodland mosquito habitats.  Another type of source reduction is the removal of artificial habitat, such as the filling of abandoned pools or collection and shredding of abandoned tires.

Education is another important aspect of source reduction.  Communicating with mosquito control recipients individually, group settings, mass mailings, or through other means allows control programs to educate property owners in mosquito biology and their preferred habitat.  Artificial containers found in the yard setting account for a large portion of the summer mosquito population in many urban areas; educating property owners about this habitat and the importance of its removal may be just as effective as trying to treat all that habitat. This communication also offers the opportunity to educate about mosquito avoidance, with respect to peak mosquito activity, and effective repellents like those containing DEET or Picaridin.  

Often, larval mosquitoes must be controlled through the use of insecticides that are applied directly into the water where larvae occur.  In such instances, presence of larvae should be confirmed with use of a mosquito dipper and visible inspection.  There are many registered larval mosquito insecticides.  Larviciding application equipment varies depending on larvicide formulation.  Application equipment for granular or pelletized larvicide formulations include hand-cranking equipment or motorized backpack sprayers.   Liquid formulations can easily be applied with compression sprayers.

Products used for Larviciding*

 Bacterial formulations.  Two bacterial formulations are available for larviciding activity:  Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus.  Both materials cause cellular breakdown in the alkaline midgut resulting in rapid death, usually within 8 to 12 hours.  It is important to note that these formulations must be ingested by actively feeding mosquitoes so they have no effect on late 4^th instar larvae or pupae.  Bti is available in liquid, briquette, and granular formulation from commercial sources under trade names such as Vectobac^®, Aquabac^® and Teknar^®.  Bti works well in a variety of freshwater habitats. Granular formulations are particularly effective against spring mosquitoes when applied during April when the larvae are the second and third stage.  B. sphaericus probably does not have the Bti’s broad spectrum of activity, but has a longer period of larvicidal activity.  In addition, B. sphaericus works well in highly organic habitats. Because of its extended control and effectiveness in organic water, B. sphaericus is effective in treating catch basins. 

Insect growth regulators.  Methoprene, trade name Altosid^®, disrupts the larval mosquito’s normal growth pattern by artificially stunting the mosquito’s development making it impossible to reach the adult stage.  It may be used to control 2^nd, 3^rd, and 4^th instar larvae.  Treated larvae will pupate but adults will not emerge from the pupal stage; it is not toxic to existing pupal or adult stages.  This product provides effective control against spring and summer floodwater mosquitoes.  Mode of delivery includes liquid, charcoal pellet, briquette, and sand granules. 

Abate^® (Temephos) is an organophosphate material delivered as a plaster pellet, liquid, or sand granule with a relatively low toxicity.  The larvicide is effective against the floodwater mosquitoes, but is often used as a larvicide in polluted larval habitats.  This insecticide has been used by the World Health Organization to treat stored drinking water.  However, careless handling or ingestion of any organophosphate increases health risks.  As with any insecticide special attention to the label is necessary relative to site use, mixing, and application of material. 

Petroleum Hydrocarbons, with trade names Golden Bear^® and Bonide^®, are highly refined mineral oils used in larviciding/pupaciding practices.  The mineral oil covers the surface of the water and then enters the breathing tubes of the larvae/pupae as they surface, making it impossible for them to breath.  This larvicide offers effective larval control in all larval habitats.

Monomolecular films, like Agnique^® and Arosurf^®, spread across the water to decrease its surface tension making it difficult for larvae, pupae, and emerging adults to attach to the water surface, causing them to drown.  These films are effective in treating mosquito habitat without significant surface vegetation.

Adult mosquito control can also be accomplished through the application of registered insecticides.  Essentially, there are three ways to accomplish this. First, adult mosquitoes can be killed on the wing during their normal flight time (dusk and dawn) using ultra-low volume (or ULV) equipment (a type of sprayer that is hand-held, mounted on a vehicle, or fixed to aircraft) and an insecticide.  This method is sometimes called "cold fogging," although the droplet size of ULV application comprises a cloud that is technically not a fog.  This is an excellent method for controlling mosquitoes, because it allows for use of a small amount of material (generally about 1-5 fl oz per acre) in tiny droplets (12-18 microns) in a narrow band of time and space.  In Michigan , malathion (an organophosphate), sumithrin, and permethrin (both synthetic pyrethroids) work well as adulticides applied as ULV.  These insecticides present minimal risk to humans when used at the labeled dosages.  In general, malathion in a ULV formulation is more effective on warmer evenings, while pyrethroids (synergized with piperonyl butoxide) are more effective in cooler evening temperatures.

A second approach to killing adult mosquitoes is using thermal fogs.  In this technology, an insecticide is heated along with another combustible material such as kerosene or oil, thus creating a fog that moves through the air, around vegetation, among flying insects.  For mosquito control, the best time to make a thermal fog application is in the evening when thermal inversion conditions exist. A thermal inversion occurs when the warm air (heated by the earth during the day) has not yet mixed with cooler air above it.  The insecticidal fog remains most stable and near the ground under conditions of thermal inversion.  Thermal foggers can be purchased commercially in sizes small enough for backyard use to sizes large enough for widescale application.  Currently, formulations of malathion, resmethrin or permethrin are recommended, follow the label directions.

Another way to control mosquitoes is to use "harborage" or "barrier" techniques.  This involves spraying a dilution of malathion (3% concentration prepared from a 50% emulsified concentration) onto vegetation surrounding the area to be protected.  This area could be a backyard, a cemetery, a park, fairway, etc. The insecticide provides a residual of active ingredient on plant leaf surfaces, and when mosquitoes fly from the harborage areas (the woods) through this zone, they die or are repelled and do not move into the open to bite.  Equipment for harborage application varies with the size of the area to be protected, but can range from a small hand pump sprayer to a motorized backpack sprayer to a large Buffalo turbine rig.  Other barrier treatments utilize synthetic pyrethroids, such as deltamethrin and tau-fluvalinate which are available under trade names such as Suspend^® and Mavrik^®, respectively. 

Products used for ULV Adulticiding*

Pyrethrin insecticides are derivatives of a substances (pyrethrums) isolated from the flowers of the chrysanthemum.  Pyrethrins are fat-soluble and act on insects to interrupt transmission of nerve impulses.  Humans quickly breakdown pyrethrins in the body; however, insects cannot breakdown pyrethrins as easily.  Hence, there is a selective toxicity to insects.  These chemicals are combined with compounds (synergists) that increase their insecticidal activity up to 300-fold.  Pyrethroids are man made chemicals with a similar mode of action to pyrethrums, but have increased chemical stability and effectiveness.  Toxicity of these substances is nonspecific in regards to insects.  Thus proper dosage, application method and timing must be followed to minimize damage to non-targets.  Pyrethrin insecticides vary in toxicity to humans, other mammals, birds, and fish so important attention should be paid to the label when utilizing this group of adulticides. 

Pyrethrins are botanical, derivatives of pyrethrums and may be registered under various trade names such as Pyrocide^®.  Are most environmentally friendly, but are often the most expensive.

Resmethrin is a synthetic pyrethroid that may be registered under various trade names such as Scourge^®.  It is used by both ground and aerial equipment.  It is a restricted use pesticide so handlers must be certified by the Michigan Department of Agriculture.

Permethrin is a synthetic pyrethroid registered under various trade names such as Biomist^® and Permanone^®. 

Sumithrin is a synthetic pyrethroid that may be registered under various trade names such as Anvil^®.  It is applied both by ground and aerial equipment. 

Organophosphate insecticides act on the nervous tissue to prevent breakdown of a substance acetylcholine responsible for nerve conduction.  This group is nonspecific regarding toxic effects on other insects, and varies in toxicity to humans, other mammals, and fish.  To prevent damage to non target organisms it is important to read, understand, and follow the label (It Is the LAW!).  Proper dosage, application method and timing will also minimize effects on non-targets.

Malathion may be registered under various trade names such as Fyfanon^®.  Used in truck-mounted ULV machines.

Chlorpyrifos may be registered under various trade names such as MosquitoMist^®.  Used in truck-mounted ULV machines.

Naled may be registered under various trade names such as Trumpet^®.  This product is primarily applied by airplane.

Always read the insecticide label before buying, mixing, loading, applying and storing insecticides.  A few adulticides available are restricted use pesticides and must be purchased and applied under the direct supervision of a certified pesticide applicator.  All applicators should review and carry the insecticide labels with them and keep MSDSs on file or with them while conducting control activities.

Since most mosquito species are night fliers, adulticiding should generally be done after sunset.  However, some species’ peak activity may occur at a time other than sunset so treatment should be adjusted to effectively control these species.  Special attention should be paid to wind direction and speed. A change in wind direction may move the material off target, while a moderate to strong wind will cause the material to disperse too quickly, lessening its effectiveness.  Spray trucks should be driven slowly; maintaining a constant 10 mph while treating.  This assures application of the insecticide at a uniform rate.

Machines must be kept in proper working order and calibrated every 40 hours of running time.  Calibration of machines may also be needed after maintenance or after changing insecticides.  Both flow rate and droplet size should be calibrated in ULV machines and flow rate in thermal foggers.  Generally, equipment manufacturers and distributors are available to aid in calibration.  When using corrosive insecticides, machines should be flushed after each use.

There should always be a basis for adulticiding, either there is a mosquito disease threat, increased adult activity in mosquito traps, or substantiated complaint calls.  Care should be taken not to waste insecticide, expose the public to pesticides unnecessarily, and promote buildup of mosquito populations resistant to the insecticides.

 Biological Control. Many organisms have been or are being evaluated as potential biological control agents for mosquitoes. A few of these agents have been used in mosquito control for years.  The mosquito fish (Gambusia affinis) has been used by the World Health Organization and others in many parts of the world since the 1940s.  A nematode parasite (Romanomermis culicivorax) has been used with measured success, but is limited by commercial availability. The release of sterile male mosquitoes into native mosquito populations has also had some success. As mentioned above, the bacteria Bacillus thuringiensis israelensis and Bacillus sphaericus have been on the market for several years, and are some of the most historically successful biological control agents currently used.

Each biological control agent has its own unique merits and restrictions.  To use a biological control agent successfully, mosquito control personnel must have knowledge of the biology of each agent used.  Some biological control agents are limited by climatic and physical factors such as temperature, oxygen availability, and organic pollution.  Some are more effective on certain types of mosquitoes than others. Biological agents also differ in the ways in which they can be formulated, transported, stored and applied.  Cost is also a factor in any responsible control program.  Parasitic nematodes and sterile male mosquitoes, for example, can be very costly due to the laboratory rearing associated with them.  All of these factors must be considered when selecting the proper biological control agent for a specific habitat or to control a specific mosquito.

Flying predators are often cited in the popular press as means for controlling mosquitoes by predation.  However, scientific studies do not support the contentions that bats, swallows, purple martins, dragonflies, or other flying predators are effective, even though these methods might sound appealing and the animals themselves have aesthetic and intrinsic value.  One has to bear in mind that predation is a natural process that is ongoing, yet we have mosquitoes anyway, often in large numbers.  Actually, birds and bats do not include many mosquitoes in their diets, despite some claims to the contrary.  The idea that they eat thousands of mosquitoes per night comes from statements in the natural history literature indicating that these predators would have to eat this many to maintain their existence.  Outdoor, electronic bug zappers with ultraviolet lights do not control mosquitoes.  So-called "mosquito plants" do not effectively repel mosquitoes, and are not recommended for this purpose despite advertisements to this effect.  Other devices such as those advertised to repel mosquitoes by high frequency sound do not actually repel mosquitoes.

There are several sources of information on mosquitoes and their management that are appropriate for Michigan conditions.  The Michigan Department of Agriculture Michigan Mosquito Manual contains material on mosquito control activities, mosquito biology, mosquito-borne diseases such as encephalitis and dog heartworm, and organizational tips.  This and other information are available from our website on the “Publications” page.  Mosquito control districts in Bay, Midland , Saginaw or Tuscola Counties have brochures and other information available.

The Michigan Department of Agriculture certifies persons who apply insecticides for mosquito control.  The certification process requires taking two examinations, one a core exam and the other a specialty exam for mosquito control (Category 7F).  Interested parties can call their local Michigan Department of Agriculture office to schedule an examination or to get further information.  Study booklets for both of these exams are available from the Michigan State University Bulletin Office and from local County Extension Services offices.  These manuals are also available on the Saginaw County Mosquito Abatement Commission website (www.scmac.org) under “Employment”.  The Michigan Department of Agriculture’s website (www.michigan.gov/mda) has the core manual available.