• Chemical Control for West Nile Virus
• Biological Control for West Nile Virus

Before an aerial application of adulticides is carried out, it is important to assess fully the rational for carrying out the application, with due consideration of the potential risks (environmental and public health) involved in relatively wide-scale application of insecticides and the potential benefits in preventing human (and horse) illness. (See section below: "Legal and Ethical Considerations")

• Prior to the start of aerial spraying it is necessary to determine the area over which the adulticide is to be applied, the chemical to be used and the time at which the application is to be carried out for maximum efficacy.
  • Maps are required which delineate both possible target areas and areas where application should be avoided. (D72)
• Rotary wing or fixed-wing aircraft may be used.
• Small amounts of insecticide are usually applied as an Ultra-Low-Volume spray.
• Organophosphates, pyrethrins or pyrethroid-based insecticides may be used.
• Application may be repeated as required: "Two to three adulticide applications spaced 3-4 days apart may be required to significantly reduce Culex pipiens [Culex pipiens complex - Northern house mosquito] populations." (D67)
• Aerial application usually occurs as soon after dawn as possible as Culex spp. are still active at this time and the wind is generally least strong, increasing efficiency of application. (V.w42)
• Following the application of adulticides, surveillance is carried out in order to assess the effectiveness of control. 

(D67, D72, V.w42, J257.168.w1)

• The goal of adulticide use is reduction in the risk of human disease by decreasing as far as possible the number of infected adult vector mosquitoes in an area. (D67)
• Adulticiding should be used as a supplement to other methods of mosquito control: source reduction, larviciding and the use of personal protective measures. (J115.13.w1, J257.168.w3, D67, D72)
• "Adulticiding based on surveillance data is an extremely important part of any integrated mosquito management program" and aerial application is one part of such a program. (D67)
• The use of adulticides should be considered only when there is evidence from surveillance programs of enzootic WN virus at a level suggesting a high risk of human infection and also the presence of abundant adult mosquito vectors. (D72, J257.168.w1)
• The purpose of the application of adulticides is to prevent human disease by interrupting the enzootic transmission cycle or by preventing transmission to humans and domestic animals. (D67)
• The use of adulticides is most likely to be considered appropriate in areas of high human population density. (D72)
  • Use in areas of low human density may be appropriate if other vertebrates such as horses are at high risk.. (V.w42)
• Aerial spraying is appropriate for application of adulticide chemicals over large areas in a short period of time. (D67, D72)
  • "This is a critical positive attribute when large residential areas must be treated quickly." (D67)
• "Aerial application is less prone to patchy coverage than ground-based application in areas where road coverage is not adequate." (D67)
• It is important to time the application of adulticides to match the peak activity periods of the target species. (D67)
• "Aerial spraying should be used only when necessary because of geographic considerations and should be limited to the immediate area where the vector  population has been documented to exist through vector surveillance and to adjacent areas considered at risk for imminent disease transmission." (D72)
• "Control of adult mosquito populations using adulticides is usually reserved as a last resort". (J115.13.w1)

• "The EPA has determined that the insecticides labeled nationally for this type of application pose minimum risks to human health and the environment when used according to the label. Adulticides labeled for mosquito control include several organophosphates such as malathion and naled. Some natural pyrethrins, synthetic pyrethroids (permethrin, resmethrin and sumithrin) also hold adulticide labels." (D67)
• Consideration should be given when using adulticides to the potential development of resistance and ways in which the onset of resistance may be prevented. (D67)
• The views of local communities regarding the potential risks and benefits of insecticide use should be considered in decisions regarding whether or not adulticides should be applied in a given area. It is important to remember that different sectors of the population may hold strong, widely divergent, views on this topic. (D72)
• Accurate guidance, using simple methods such as flags on poles or more sophisticated methods such as GPS, produces more efficient and effective dispersal of adulticides. (W175.Nov01.WNV1)

• "Mosquito adulticides should be considered the least desirable method of control and only used when current isolations of virus and/or evidence of disease has been established." (D72)
• "If adulticides are used, either by land or aerial application, people may be exposed to them. Pesticide exposure carries some inherent risk to people." (D72)
• Adulticiding is typically less effective and less target-specific than larviciding. "Adulticiding, the application of chemicals to kill adult mosquitoes by ground or aerial applications, is usually the least efficient mosquito control technique." (D67)
• "For adult mosquito control, insecticide must drift through the habitat in which mosquitoes are flying in order to provide optimal control benefits." (D67)
• Most Culex spp. mosquitoes are nocturnal; since many applicators will not fly at night, this reduces the effectiveness of airborne applications in control efforts aimed at Culex species. (D67)
• Effectiveness can be assessed only if appropriate mosquito surveillance systems are in place to allow comparison of mosquito populations before and after the application. (D67)
• "In general, the finding of a WNV positive bird or mosquito pool does not by itself constitute evidence of an imminent threat to human health and warrant mosquito adulticiding. Adulticiding should be considered only after careful consideration of the WNV risk to human health by taking into account multiple factors, including documentation of the presence of West Nile Virus in the area, the numbers and species of the vector populations, the vectors’ physiologic age, the density and proximity of human populations, the time of year, weather conditions, physiography of and accessibility to the area where the vector is located, rapidity of response required as determined by the seriousness of the public health threat, potential impact on people and the environment, and the likelihood that vectors in nearby areas not subject to control measures will migrate from the area if not subject to control. In general, ground application of pesticides should be the preferred method of control. Aerial spraying should be used only when necessary because of geographic considerations and should be limited to the immediate area where the vector population has been documented to exist through vector surveillance and to adjacent areas considered at risk for imminent disease transmission." (D72)
• The effect of adulticides is transient (a few days) unless spraying is repeated. (J257.168.w1)
• Adulticide sprays are inappropriate for use during inclement weather conditions such as high winds, rain or fog as the chemical needs to hang in the air and in such conditions it will rapidly reach the ground and be inactive against the mosquitoes. In cold conditions (below 55-60°F) aerially applied sprays lose efficacy because mosquitoes are slower and spend more time resting in areas where the chemical mist is less likely to reach such as in leaf litter. (D72)
• Adulticide use may be inappropriate in areas of low human population density (D72); unless other vertebrates such as equines are at high risk. (V.w42)
• Aerial spraying, applying insecticide over a large area, is a non-selective means of applying such chemicals. (D71)

• Aircraft and spraying equipment capable of applying the mosquito adulticide chemical at the correct rate and droplet size.
  • Commercial companies such as Clarke Environmental Mosquito Management, based in Chicago, possess appropriate aircraft.
  • The U.S. Air Force has a special unit with appropriate C-130 airplanes equipped to conduct large area emergency adulticide application. (V.w42)
• Appropriate adulticide chemical (organophosphates, pyrethrins or pyrethroid-based insecticides).
• GPS equipment if possible to guide aircraft accurately and monitor spray track. (D67, W175.Nov01.WNV1)

• Considerable expertise regarding epidemiology and control of vector-borne diseases is required in order to determine whether and where aerial application of adulticides is required. 
• Experienced pilots are required to carry our aerial spraying.
• Training is required in the safe handling and use of the insecticide to be used.

• Aerial application of adulticides is expensive due to the equipment (aircraft and sprayers) and personnel (appropriately trained pilots) required.
• The cost of aerial application may be less than that for ground-based application of mosquito adulticides if application to large areas is required. (D67)

• The potential environmental impact of mosquito adulticides must be considered. This may be direct (action of the insecticidal substance on non-target species) or indirect, e.g. reduced food availability for species which normally feed on mosquitoes or other affected species, reduced availability of affected insects for plant pollination.
  • "The use of insecticides for mosquito control is accompanied by risks to non-target organisms and ecosystem function. Direct toxicity is the primary concern, and it may be reflected in fish or wildlife kills or in episodes of non-lethal effects which render exposed organisms susceptible to other sources of morbidity or mortality." (D72)
• Potential risks to human health, including impact on the operator and on the human population of the area sprayed: "If adulticides are used, either by land or aerial application, people may be exposed to them. Pesticide exposure carries some inherent risk to people." (D72)
• Chemicals used in aerial application of adulticides must be licensed for such use: "Material choice for ground or aerially applied mosquito control in public health emergency situations is limited by EPA restrictions on the pesticide label and applicable state and local regulations." (D67)
• Federal and state legislation must be complied with in any use of insecticides. Application of insecticides must be approved by state agencies.
• It is important to ensure that the public are notified of when and where adulticides are being applied. (D72)
  • State and local (e.g. county, city, mosquito control district) requirements regarding notification of the public prior to the use of insecticidal sprays must be complied with.