Mosquito Control

1451 Peters Mountain Road, Dauphin, PA 17018 Phone: 717-921-8100

Program Coordinator: Eric A. Naguski email: enaguski@dauphinc.org

Mosquito Control

Control of mosquito larvae is accomplished through proper water and land use management, in conjunction with the EPA-approved larvicide program, when required. Larvicides come in four basic types, each possessing a different mode of action. Stomach poisons must be ingested; Bacillius thuringiensis israelensis (or B.t.i.) and Bacillus sphaericus (B.s.)are live bacterial spores that produce a toxin when it comes in contact with the chemicals in the mosquitoes’ gut. Growth regulators include methoprene, which is a hormone that prevents the larvae from eventually molting to an adult. Surface films inhibitors include ®Agnique MMF, which reduces the surface tension of the water, making it impossible for the larvae to attach their breathing tubes at the surface, thus drowning them. Others may physically obstruct the breathing apparatus of the larvae, in effect suffocating them.

Because these larvicides are to be used in sensitive aquatic environments, they are specifically designed to minimize their impact on non-target organisms. They must be applied, by law, only to a predefined target site following guidelines that are specified on the label. To ensure its effectiveness, the application rate for each larvicide is calculated on the basis of its toxicity profile and degradation characteristics. The Dauphin County mosquito control program uses four larvicides: B.t.i., B.s., Methoprene, and ®Agnique MMF.

Mosquito Control Strategies in Dauphin County

Dauphin County West Nile Virus Control Program will consider, when practical, alternatives to biological and chemical pesticides. Among these alternatives source reduction will be the primary goal. If alternatives to pesticide use are not available, the lowest effective amount of pesticide product per application and the optimum frequency of applications necessary to control the pest will occur, by choosing the lowest effective application rate for a specific pesticide, in a specific mosquito breeding habitat, under specific environmental conditions. Prior to the application of pesticides, Dauphin County Conservation District will evaluate the following management options, considering impact to water quality, impact to non-target organisms and pest resistance:

a. No action

b. Prevention

c. Source Reduction

d. Education

e. Biological control agents

f. Pesticides

*It is important to consider how each of these techniques can be employed in mosquito management. A-F must be considered, but might not be practical when managing mosquitoes for human disease.

*Another important consideration is the use of surveillance to document thresholds and efficacy of applications. Specific information on thresholds can be found here. Other considerations should include species, vegetation density and previous application dose.

There are many areas within Dauphin County that provide suitable habitats for mosquito reproduction. Those areas can be subdivided and classified as follows:

1.Floodwater breeding sites

2.Container breeding mosquito sites

3.Wastewater treatment facilities

4.Permanent water breeding sites

5.Catch basins (stormwater structures)

Each of these habitats produces specific mosquito species and has specific habitat characteristics that require different mosquito control strategies and pesticides. Ultimately the elimination of breeding sites and public education are the ultimate tool for mosquito population size reductions, so recommendations to property owners to do so will be the primary goal of the Dauphin County West Nile Virus Control program in our efforts to lower the risk of human acquisition of mosquito-borne disease. In those instances where it is impossible to eliminate the habitat, pesticides will be used following a triggering event. Those triggering events will most often be in the form of mosquito surveillance (both larval and adult), or stemming from citizen complaints. Table 1 shows the Dauphin County pest management area descriptions and the recommendations of the Dauphin County West Nile Virus Control Program and the pesticides used in the specific habitat types in Dauphin County.

Table 1. Dauphin County Pesticide Application Site Descriptions

Site Name	Triggering Event	Mosquito species	Recommendations	Pesticides that may be used if recommendations cannot be met
Dauphin County Floodwater Mosquito Breeding sites	Larval mosquito surveillance following a rain event	Aedes, Ochlerotatus, and Psorophora spp.	Proper maintenance of stormwater BMP structures, enact and enforce local mosquito breeding codes	Bacillus thurengiensis var. israeliensi; Methoprene, Poly (oxy-1,2-ethanediyl), α-(C16-20 branched and linear alkyl)-ω-hydroxy (100%) monomolecular film
Dauphin County Container Breeding Mosquito sites	Larval mosquito surveillance	Aedes albopictus, Aedes triseriatus, Culex pipiens, Culex restuans	Elimination of breeding habitats; enact and enforce local mosquito breeding codes	Bacillus thurengiensis var. israeliensi; Bacillus sphaericus; Methoprene; Poly (oxy-1,2-ethanediyl), α-(C16-20 branched and linear alkyl)-ω-hydroxy (100%) monomolecular film
Dauphin County Wastewater Treatment Facilities	Larval mosquito surveillance	Culex pipiens, Culex restuans, Culex salinarius, Anopheles punctipennis, Anopheles quadrimaculatus	Eliminate/cover off-line tanks, make sure all tanks are circulating water at a sufficient velocity to prevent mosquito activity, enact and enforce local mosquito breeding codes	Bacillus thurengiensis var. israeliensi; Bacillus sphaericus; Methoprene; Poly (oxy-1,2-ethanediyl), α-(C16-20 branched and linear alkyl)-ω-hydroxy (100%) monomolecular film
Permanent Water Mosquito Breeding Sites	Larval mosquito surveillance	Culex pipiens, Culex restuans, Culex salinarius, Anopheles punctipennis, Anopheles quadrimaculatus, Culiseta melanura	Eliminate habitat, enact and enforce local mosquito breeding codes	Bacillus thurengiensis var. israeliensi; Bacillus sphaericus; Methoprene; Poly (oxy-1,2-ethanediyl), α-(C16-20 branched and linear alkyl)-ω-hydroxy (100%) monomolecular film
Urban and Suburban Catch Basins in Dauphin County	Larval Mosquito Surveillance, prophylactic treatments	Culex pipiens, Culex restuans, Aedes albopictus, Aedes triseriatus	maintain catch basins, enact and enforce local mosquito breeding codes	Bacillus thurengiensis var. israeliensi; Bacillus sphaericus; Methoprene; Poly (oxy-1,2-ethanediyl), α-(C16-20 branched and linear alkyl)-ω-hydroxy (100%) monomolecular film
Urban, Suburban Residential and Agricultural Areas in Dauphin County	High numbers of adult mosquitoes in traps and/or positive test results from adult samples collected in a specific area	Culex pipiens, Culex restuans, Culex salinarius, Ochlerotatus spp., Aedes spp., Psorophora spp.	eliminate larval breeding areas, larval mosquito control	permethrin; prallethrin; sumithrin; pyrethrins; piperonyl butoxide

Product Choice and Dose

General considerations - Products are chosen based on the mosquito species, life stage of the mosquito and the application habitat. Pretreatments in areas that are expected to hold water throughout the season are an important tool in suppressing mosquitoes throughout the year. Careful measurement of the treatment area must be made in order to apply the correct amount of pesticide needed to achieve efficacious mortality in the mosquito population.

Table 2 shows the pesticides used in specific habitats by the Dauphin County Mosquito Control program.

Table 2. Mosquito Control Products used by the Dauphin County WNV Control Program

(Clicking here will take you to a webpage with the label and MSDS for the products used by the Dauphin County Mosquito Control Program.)

Product	Target	Habitat	Dose
Vecto Bac, Teknar, Mosquito Dunks	Larval Mosquito	Floodwater, containers, catch basins, Wastewater Treatment Facilities	1-20lbs/Acre
Vectolex	Larval Mosquito	Organic water, catch basins	1-20lbs/Acre
Altosid	Larval Mosquito	Floodwater, containers, catch basins, Wastewater Treatment Facilities	5-20lbs/ Acre
Agnique (Monomolecular film)	Pupae	Water Surface	1 squirt/50 sq. feet
Duet	Adult Mosquito	Air Column	0.41 – 1.23 fl oz/acre
Anvil 2+2	Adult Mosquito	Air Column	1.081 to 3.245 fl.oz. of the undiluted spray per acre
BioMist 3+15	Adult Mosquito	Air Column	.75-3oz/Acre
Flit 10EC	Adult Mosquito	Foliage	6oz/gal

* If action thresholds have been exceeded and the mosquito population is unable to be controlled through source reduction, application of pesticides is warranted. If pesticides are chosen to control mosquitoes, the primary method is through the use of biological pesticides. B. thuringiensis israelensis and B. sphaericus are important tools mosquito control professionals have at their disposal. B. thuringiensis israelensis and B. sphaericus will kill larval mosquitoes within 24 hours of application. B. thuringiensis israelensis has no residual effect, while B. sphaericus has a residual effect because of the spore’s thicker cell wall. Both bacteriological strains have excellent environmental profiles and do not impact non-target species. Another important tool for the control of larval mosquitoes is Methoprene. Methoprene is an environmentally safe product and has a proven track record of excellent results. Methoprene is a hormone disrupter; therefore larvae must be reared out to adults in order to judge the final efficacy of the application.

None of the aforementioned products in this section will impact mosquito pupae. When pupae are present, monomolecular films must be used to achieve mosquito control. These films have the potential to impact other aquatic organisms using surface tension.

The final tool available to a mosquito control professional is the use of chemicals to control an adult mosquito population. When adult mosquito thresholds are exceeded, steps need to be taken to reduce the population. Application methods include barrier and ultra-low volume aerosolized treatments. Products chosen for these uses are applied by their respective label.

Thresholds

The Dauphin County West Nile Virus Control Program has developed mosquito surveillance thresholds that will dictate what, if any, mosquito control will take place in a given area. These thresholds must be surpassed before any adult mosquito control activities are taken. All final decisions concerning adult mosquito control in Dauphin County will be made by the Dauphin County West Nile Virus Control Program Coordinator, taking into consideration mosquito and disease surveillance results, human population dynamics, environmental factors, and budgetary concerns. There may be, at times when even though our surveillance efforts show high numbers of target mosquitoes in an area, that due to one or all of these other factors, adult mosquito control will not be possible. This decision will be made by the coordinator.

A. Disease Vectoring Mosquitoes

Mosquitoes implicated in the transmission of West Nile Virus include: Culex pipiens, Culex restuans, Culex salinarius, Aedes vexans and Ochlerotatus trivittatus. Other diseases such as Eastern Equine Encephalitis and Lacrosse Encephalitis should be considered if an area has habitats that respectively maintain populations of Culiseta melanura and Coquillettidia perturbans or Ochlerotatus triseriatus.

Thresholds have been established for each of these species and take into consideration the potential vectoring capacity of non-diseased and diseased mosquitoes.

>500 Culex restuans mosquitoes found in any single gravid trap prior to the detection of West Nile virus

>300 Culex pipiens mosquitoes found in any single gravid trap prior to the detection of West Nile virus

>150 Culex mosquitoes found in any single gravid trap after the detection of West Nile Virus in the County

>75 Culex mosquitoes found in any single WNV infected oviposition trap

>25 Culex mosquitoes found in any single WNV infected host seeking trap

>25 Culex mosquitoes found in any single WNV infected trap after the report of a human or horse case of WNV.

B. Nuisance Mosquitoes

Dauphin County has a variety of different mosquito species that have the potential to be a nuisance for residents. These species include: Aedes vexans, Aedes albopictus, Psorophora ferox, Psorophora ciliata, Psorophora columbiae, Ochlerotatus canadensis, Ochlerotatus stimulans, Ochlerotatus trivittatus, Ochlerotatus sticticus and Coquillettidia perturbans. Thresholds must be established for the treatment of these mosquitoes

>100 Nuisance mosquitoes collected as a result of routine host seeking mosquito surveillance

>50 Nuisance mosquitoes collected as a result of a complaint

>50 Nuisance mosquitoes found infected with a transmissible human disease

C. Larval Mosquito Thresholds

1. Treatments of larval mosquito habitat may be conducted in areas that are found to contain an average of at least 1 larva per dip (using a standard 12 oz. dipper). Actual treatments will be based on local demographics, mosquito species present, and other historic and current conditions.

2. The storm water system may be treated in selected areas of the county where vector species have been found or there is a history of arbovirus activity.

3. A limited number of known, historic breeding sites may be treated because after a major rain event there is insufficient time to inspect and treat all larval sites within the county.

D. Frequently Asked Questions about Adult Mosquito Control

1. Should I wash toys and other items in the yard at the time of the application?

While you can, if you wish, it is not necessary to wash items in your yard after the application. Due to low application rates, any exposure from contact with these surfaces would be low and pose negligible risks.

2. Should I cover the pool before the application?

No, residue in a pool would be low and also diluted by the water in the pool.

3. Should I close the windows and turn off my air conditioner?

The ULV vapor disperses readily, and little movement of the material into open windows with screens is expected. However, individuals with upper respiratory problems, such as asthma, may react to ULV applications. Closing windows and turning off air conditioners is recommended for those with upper respiratory problems.

4. How long should I wait before I let my pet out?

When the chemical is applied at the labeled rates there are wide margins of safety for humans, dogs, cats and other mammals. Indoor pets may be "let-out" immediately following the application. Outdoor pets may be left outdoors.

5. How long should I wait before allowing the children to enter the yard?

The ULV vapor disperses very quickly after the application. Individuals with respiratory problems may react to ULV application. People with these health issues may want to wait an hour before resuming outdoor activities in treated areas.

6. How do I get on your no-spray list?

Call the Dauphin County West Nile Virus Control Program office at 717-921-8100