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 larval 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 an incandescent 25 watt light bulb to attract mosquitoes. The trap is limited in location in that it uses 110 volt AC. Homeowners, 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. When baited with CO2 only, it collects exclusively female mosquitoes often in large numbers compared to light only traps.
• Gravid Traps, like oviposition jars, use a dark container (plastic tray) with an organic-water mixture as the attractant. They are lightweight, 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 WN 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.