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Components of a Local Program

No one method alone can provide enough information to assess the risk of disease transmission in an area; instead, it is necessary to rely on a combination of methods.  Surveillance and subsequent monitoring of mosquito populations should be the first step and is an essential component of any proactive mosquito control program.  Surveillance involves identifying likely problem areas within your local area.  Monitoring involves routine and regular assesment of what is occurring in those specific areas.

In addition to surveillance and monitoring of adult and larval mosquito populations, it is also necessary to survey and monitor for evidence of viral agents.  Local mosquito control programs can request the assistance of state personnel in setting up the most efficient surveillance and monitoring program for specific areas.  

Surveillance and Monitoring Techniques: 

Citizen Complaints

At the very least, any pro-active mosquito control program should have a citizen-complaint line available and maintain careful records of any complaints received. See the link for a sample ‘complaint log’. Records should include the location of the complaint as well as other pertinent information (nature and extent of the problem, including frequency of bites, how long this has been a problem, and the time of day most bites occur).

• Usual or unusual:  If the citizens indicate that this is an unusual occurrence, investigators can look for changes that may have occurred recently, providing a clue to the source of the breeding zone. If this is a continual or re-occurring problem, investigations can lead to identification of a zone that would benefit from larval control methods.
• Map Complaints:  Either through the use of paper maps or one of the many free internet mapping services available, mosquito control personnel can look for clusters of complaints that may provide clues to a problem breeding area nearby. Mapping can indicate if there is a cluster of complaints in one area that then warrant further investigation.
• Time of Day: If the bites occur during the day, investigators can look for potential breeding sites for Ae. albopictus, recommending a ‘tip and toss’ approach. Spraying may not be desireable or effective in these instances.

Mosquito Population Counts

In addition to citizen complaints, the pro-active mosquito control program should do surveillance for the number of mosquitoes in a given area.  Instead of relying on anectodal information, keeping track of the number of mosquitoes in one or more areas over time can give the control program manager valuable information about the nature and scope of the problem in similar areas.   Preferably, the control program will set traps on a routine basis and keep records of the number of mosquitoes caught in the trap. Separating the adult mosquitoes into male and female can give the control program manager an idea if there is a new brood coming off within the next few days. Since males typically hatch first, a higher number of males in the trap is an indication that the females, which bite, are soon to hatch.

Identification of the mosquitoes in the trap to genus or species will provide additional information about the diversity in the area and can greatly help to identify the source of the problem areas. A New Jersey trap is permanently mounted in an area, and requires electricity.  CDC light traps are battery operated and require either dry ice or carbon dioxide gas cannisters.  Gravid traps attract females about to lay eggs and require liquid, typically water to which grass clippings or leaves have been added and allowed to ferment.  This process encourages the growth of bacteria which is the food source for the hatching larvae.

Although not recommended because of the risk of disease transmission, an alternative method is to conduct landing counts, counting the number of mosqutioes that alight in a specified period of time.

By maintaining careful records of the number of adult mosquitoes present in a routine manner, the control program manager can easily discern whether the mosquito population in an area is unusual and further investigation or a change in program is required.  In addition, any of the methods outlined above will provide the program control manager with evidence to request expansion of their program or justification after a natural disaster as required by FEMA officials (Federal Emergency Management Association).

Larval Population Counts

A more targeted approach is to sample mosquito larvae in the water, before they hatch. By surveying for representative pools of standing water, the program control manager can more effectively anticipate when adult mosquito populations are more likely to cause problems for the citizenry. The simplest method is to use a small white plastic cup or a specially designed dipper to collect and count the number of mosquito larvae per dip.  As with adult mosquitoes, identification of genus and species can further assist the program control manager in assessing the severity of the problem. Another approach is to raise the larvae to adult hood in a rearing trap, either purchased or home-made, and identifying the adults to genus and/or species.

Monitoring

Surveillance expands into monitoring when records are kept over time and analyzed to identify patterns not only in the numbers of mosquitoes, but in their seasonal distribution.  Once mosquito or larval identification skills have been acquired, species diversity can also be revealing of the nature and scope of the mosquito population under consideration. 

Surveillance for Virus

In addition to monitoring mosquito populations, it is important to monitor for the presence of virus. Passive surveillance methods include keeping records of virus diagnoses in the local veterinary population as well as humans. North Carolina has participated in the use of sentinel flocks for over 20 years.  In addition, the local program can request that trapped mosquitoes be tested for the presence of virus.  Please contact your local Public Health Pest Management representative for more information.