Mosquito Management
Integrated Mosquito Management
Surveillance
and IdentificationHome
Mosquito Management
Integrated Mosquito Management
Surveillance
and Identification
The following is taken wholly from Chapter 3 (Mosquito Surveillance and Environmental Monitoring) in the Florida Mosquito Control White Paper developed by the Florida Coordinating Council on Mosquito Control. 1998. Florida Mosquito Control: The state of the mission as defined by mosquito controllers, regulators, and environmental managers. University of Florida; Vero Beach, FL, USA
This chapter discusses the importance and legal obligations regarding mosquito and nvironmental surveillance systems. Included are discussions of how to develop, design, and implement surveillance systems and commonly used methods to inventory breeding sites, collect immature and adult mosquitoes, and environmental parameters.
Mosquito surveillance is a prerequisite to an effective, efficient, and environmentally sound mosquito control program. Surveillance is used to define the nature and extent of the mosquito problem and to gauge daily mosquito control operations. It provides a basis for evaluating the effectiveness of control operations, the data needed to comply with state rules and regulations regarding the justification for treatments, and a basis for evaluating the potential for transmission of mosquito-borne diseases.
Surveillance is most effective when combined with an ongoing program for monitoring meteorological, astronomical and environmental factors that may influence mosquito population change: For example, rainfall and ground water levels, temperature, relative humidity, wind direction and velocity, tidal changes, lunar cycles, storm water and wastewater management, and land use patterns.
The objectives of this chapter on mosquito surveillance and environmental monitoring are to characterize environmental surveillance systems and to provide a general review of Florida mosquito control programs. (Programs that monitor the transmission of mosquito-borne encephalitis virus are described in Chapter 8.)
Ideally, the structure of a surveillance system should be based on the needs of the mosquito control program. Moreover, these needs should define the components of the control program as well as the budget required to implement them. In fact, the process often is reversed. Control programs are funded at a specific level, generally without a needs-assessment process. The program director is then required to meet all mosquito control needs within the constraints of a fixed budget. When funding for this process is inadequate, the result is incomplete surveillance and reliance upon control methods that work well but which may be undesirable or less effective than other more expensive methods.
The steps in developing a surveillance program as part of an overall mosquito control effort are:
• Define the mosquito problem(s)
• Define the parameters on which the control program is based
• Identify appropriate survey methods as decision-making aids regarding where and when to implement control
There are more than 75 mosquito species in Florida; individual counties may have 40 species. Fewer than two dozen species throughout Florida are important enough as pests or vectors to warrant control. However, in a given locality, this number is usually less than five. The first step in determining which mosquito must be monitored is to determine which species cause problems. Control efforts can be justified when a mosquito poses a nuisance or is an economic or health-related pest or vector. A nuisance mosquito bothers people, typically in and around homes or in recreational areas. An economically important mosquito reduces property values, slows economic development of an area, reduces tourism, or adversely affects livestock and poultry production.
One definition of a health-related mosquito problem is the ability of a mosquito to transmit infectious disease. In Florida, this definition includes only mosquitoes that spread dog heartworm, St. Louis encephalitis (SLE), and eastern equine encephalitis (EEE). However, nearby in the Caribbean and Central America, other mosquito-transmitted diseases are common (e.g., dengue, malaria). Any mosquito that bites or annoys people can be considered a health problem, particularly for individuals who are allergic to mosquito bite or suffer from entomophobia, (i.e., a fear of insects).
A list of important mosquito species can be compiled from a review of the literature for species that bite humans or which may vector disease in the area of concern. Once the target species have been identified, the affected area is surveyed for the presence of these species. The survey should be conducted as needed and should include the collection of adult mosquitoes and larvae. Information from the survey can be used to determine the abundance and seasonal distribution of each species and its relative importance as a target for control efforts. Because mosquito collection methods differ in their effectiveness for sampling different species, more than one collection method may need to be used to accurately determine the seasonality and abundance of all the species in an area. Comparing the numbers of a single mosquito species collected in different types of traps can be misleading and should be avoided.
Once the list of potential target mosquito species has been compiled, two additional questions must be answered:
• Which species, in fact, cause problems?
• How do we determine where and when each species will cause a problem?
As noted earlier, the answers depend on the mosquito species, the available budget, and the proposed means of mosquito control. In Florida, temporal and spatial changes in mosquito populations and the problems that mosquitoes cause are measured by monitoring three factors: Telephone requests for mosquito control services, adult mosquito population, and immature mosquito populations. Not all mosquito control programs in the state monitor every component, however. Each of these three elements is discussed below.
One method for ascertaining a nuisance mosquito problem is through telephone service requests. Most Florida mosquito control programs have a telephone number citizens can call to request mosquito control services. Service requests generally are related to specific mosquito species or groups of similarly behaved species, although the mosquitoes that cause service requests vary considerably from one area to the next. In most cases, service requests are an acceptable basis for meeting state requirements for monitoring mosquito problems to justify control. An exception can be made in environmentally sensitive areas or in areas where there is some objection to pesticide application. Telephone service requests always should be verified as to their validity.
Service requests are handled in a variety of ways. Most programs record the information on data sheets, although some record them using computer programs linked to a General Information System (GIS). The data sheets typically are used for one or two days for determining where control activities must be concentrated. Typically, an inspector will be sent to verify the service request in areas not indicated as having a mosquito problem by other surveillance techniques. In some cases, changes in the numbers of calls from one day to the next are used to evaluate the effectiveness of control operations, particularly aerial adulticiding. If the cause of the service request is a container-breeding mosquito species, such as the Asian tiger mosquito (Aedes albopictus), Ae. aegypti, or certain Culex species, inspectors may be sent to the caller's address to identify the mosquito species and to assist with the correction of a selfgenerated problem. If the request results from floodwater mosquitoes (saltwater or freshwater) or permanent water mosquitoes such as Anopheles, Coquillettidia or Mansonia, the caller usually is informed regarding what will be done to correct the problem. Whenever the call is from a new or unexpected location, an inspector is sent to determine if a new breeding site is involved.
Perhaps 90% of the mosquito control programs in Florida use one or more methods to measure adult mosquito populations before a control decision is made. The two methods used most often are Landing Rates and Mechanical Traps. The purpose of monitoring adult mosquitoes is:
• To determine where adults are most numerous
• To substantiate telephone service request claims of a mosquito problem
• To provide data that satisfies Florida Statutes (F.S.) as a basis for applying adulticides
• To determine the effectiveness of source reduction, larviciding, and adulticiding control methods
Florida Administrative Code 5E-13.036 dealing with mosquito surveillance is concerned only with the monitoring of adults. According to these statutes, before adulticides can be applied, a monitoring program must detect an increase in the population above a predetermined baseline, collect more than twenty-five mosquitoes in a single trap night, or collect more than five mosquitoes per hour of operation. The rules do not specify the type or number of traps or the species or sex of the mosquitoes, but they make illegal the application of adulticides when mosquitoes are not present. This rule was initiated in the mid-1980s and, for the first time, forced many mosquito control programs to use mosquito surveillance to justify spraying. And, while many of these programs had a monitoring network (most frequently New Jersey Light Traps [NJLT]), collections of mosquitoes usually were not identified at the site of collection or in a timely manner and were not used for daily control decisions.
Landing rates are a frequently used method for measuring adult mosquito activity. The technique comprises a count of the number of mosquitoes that land on a person in a given amount of time. Landing rates are effective for monitoring salt-marsh mosquitoes, which bite during the early morning and during the day. Landing rates also are useful for evaluating activity in day-biting, container-breeding (including bromeliad) mosquitoes, which are common around homes.
The specific method used to determine landing rate varies among programs. Important variables are the time of day at which observations are made, the duration of observations, the portion of the subject's body observed for landing mosquitoes, the number of body sites examined, and the number of human subjects used. It is not important that specific procedures for assessing landing rate differ between programs. As long as the same protocol is observed at a given site, it will reflect the biting population at that site on that date. It is also important that the same individual assess biting rates at the same site from one date to the next.
The New Jersey Light Trap (NJLT) was first used in a statewide program in the mid-1950s by the Florida Board of Health mosquito control program. Local programs would operate the traps and send the collections to Jacksonville for identification. Later mosquito identification became the responsibility of the local programs. At that time, many programs that lacked expertise in mosquito identification stopped trapping. Because NJLTs, which require 110 VAC power, have been operating in the same locations for decades, the historical monitoring data have been valuable for documenting the long-term changes in mosquito populations in certain parts of the state. While NJLTs are usually operated overnight, the number of trap sites and the frequency of trapping vary among mosquito control programs. Currently, there are no rules of thumb, established standards, or state rules that apply to the design used for placing or operating NJLTs.
Many programs, even some that use NJLTs as their primary survey tool, use Center for Disease Control light traps (CDC) to monitor adult mosquitoes. The CDC trap is a miniature version of the NJLT that operates on six volts DC and can be used anywhere. It costs less to purchase than the NJLT, does not require permanent installation, and collects primarily mosquitoes. Although there are several manufacturers of CDC traps, they can be handmade by local mosquito control programs for about one-fourth the retail cost. This has resulted in a proliferation of different designs for the trap. It is not important that all control programs use the same CDC trap design as long as the same model of trap is used within a program. Some mosquito control programs use carbon dioxide (either dry ice or bottled gas) or octenol as a supplement for the CDC trap. Some control programs operate CDC traps for a few hours a night, and others operate them overnight. The main reasons for these variations are budget related, rather than entomological. As with the NJLTs, there is no standard design for placing or operating CDC traps.
Two programs in Florida use methods other than light traps as their principal adult mosquito surveillance tool. Pasco County Mosquito Control District (MCD) uses permanently located unbaited suction traps. Lee County MCD uses truck traps. A truck trap is a large screened funnel attached to the top of a pickup truck. Unlike the NJLT and CDC traps, suction and truck traps sample all airborne mosquitoes, which provides a better measure of mosquito density but does not measure the biting mosquito population. Lee County MCD has operated truck traps for more than 30 years. The data have been very useful for making control decisions for salt-marsh mosquitoes. In addition, Lee County MCD uses a network of CDC traps to monitor mosquito populations. Pasco County MCD uses CDC traps to identify localized mosquito problems.
Typically the application of larvicides in locations where source reduction is not an option is preferred to adulticiding. This procedure minimizes the area treated and the amount of chemicals used.
If the design of the mosquito control program includes source reduction or application of larvicides, both a mosquito-breeding site inventory (electronic and/or hard copy) and a larval surveillance system should be in place. The mosquito-breeding site inventory is a permanent collection of descriptions of all breeding sites. A larval surveillance system describes the numbers of mosquitoes breeding at each site. Inventory and survey data can provide a record of mosquito breeding over time, whereas data in the larval surveillance program are useful for one or two days.
As part of a comprehensive effort, a mosquito control program will have maps that show the location of all the mosquito-breeding sites in its jurisdiction. These maps are used to develop and maintain a program for the surveillance of larvae and the application of larvicides. The maps are an up-to-date record of the breeding sites within the jurisdiction of the control program.
The map inventory must be updated on a routine basis. As new residential or commercial developments are created, the characteristics of mosquito-breeding sites may change. In turn, the species composition of mosquitoes produced at each site may change.
Deciding which characteristics of the breeding site should be recorded in an inventory is difficult. Instantaneous measurements of rapidly or frequently changing variables, such as water depth, water temperature, and presence or absence of predators or parasites, may be useful to help determine if treatments are needed, but should be included in a mosquito-breeding site inventory.
While the field work portion of the initial inventory is time consuming, creating and maintaining hard-copy maps of breeding sites is even more difficult. It is highly desirable to use a computerbased mapping system for this purpose if possible; currently, several such methods are available.
An advantage of a computerized mapping system is the ease with which data can be extracted and compiled.
The number of devices and procedures that have been developed to sample mosquito eggs, larvae, and pupae is extensive (Service 1993). Unfortunately, little effort has been placed on the standardization of popular methods. Each mosquito control program has its own version of the different sampling methods, which makes the comparison of data between programs difficult.
There are many techniques for sampling populations of mosquito eggs, but these methods are seldom used on an ongoing basis or as a primary surveillance system. Sampling for mosquito eggs is too labor-intensive for practical purposes, and it is usually easier and simpler to sample larvae. One exception to the above is the use of ovitraps, which are used to monitor the distribution of the Asian tiger mosquito, Ae. albopictus, and Ae. aegypti, in Florida. Using a network of highly attractive ovitraps to monitor this species is easier than searching for the small containers in which this species oviposits.
Mosquito larvae and pupae can be collected with dippers, nets, aquatic light traps, suction devices, and container-evacuation methods. The most commonly used apparatus is the dipper. The term "standard pint dipper" is used in the scientific literature, but in practice, there is no standard dipper or standardized dipping techniques. The dipper can be used as a survey tool simply to determine the presence of larvae. However, standardized sampling methods are required if mosquito densities are to be quantified. Such a method usually involves taking additional dipper samples of a specified quantity from designated areas in the counting habitat and then counting the larvae in each dip. Most control programs use some measure of larval density as a basis for control action.
To maximize the usefulness of mosquito surveillance data, it is important to monitor certain environmental parameters such as rainfall. Tide levels in coastal areas are monitored using charts and tide gauges. Tidal activity and rainfall dictate when high marsh sites will be flooded and when they will need to be inspected for mosquito larvae. The tide gauges may also reflect changes in the water level caused by rainfall and wind that may cause mosquito production in salt marshes and mangrove forests. Rain gauges are important in both coastal and inland counties -- in fact, anywhere mosquito production is being monitored. Data from these instruments can be supplemented with data from the Natural National Weather Service and local weather watchers.
Because rainfall in Florida is highly localized, it is important to collect rainfall data from many locations. Knowledge of weather patterns is important during aerial or ground application of mosquito adulticides. High winds, low temperatures, rainfall, and high humidity can affect activity, as well as the dispersal of the adulticide.
Service, M.W. 1993. Mosquito ecology: field sampling methods, 2nd ed. London and New York: Elsevier Applied Science, 988 pp.