Credit: Photos: MMCD
Catch-basin maps help St. Paul's Metropolitan Mosquito Control District organize and monitor mosquito breeding sites.
A Metropolitan Mosquito Control District employee tracks levels of mosquito larvae in natural wetland.
Winter and early spring are ideal times to evaluate past mosquito control efforts, or to develop or fine-tune a program. Mosquitoes ruin outdoor activities and chase away potential revenue; they also carry life-threatening diseases. For example, West Nile virus has caught the nation's attention since the first human case in North America was reported in 1999. Other mosquito-transmitted diseases include St. Louis encephalitis, Western equine encephalitis, dengue, and canine heartworm.
The good news: It's possible for a public works department to create and implement an effective control strategy. Armed with a basic understanding of habitat and biology—and with help from mosquito control products—you can develop a sound plan.Taking Steps
Step 1: Plan. Begin by devising a plan that considers the extent of your problems and the resources needed to carry out the solution. An integrated plan combines education, monitoring, inspection, mapping of breeding sites, eliminating unnecessary standing water, and treatment. There are many ways to exploit the mosquitoes' own biology and behavior, and to use cost-effective, carefully timed product applications.
Step 2: Organize. Every good program begins with a good organization. People, funding, equipment, and planning are essential. Once the organization and plan have been established, the next step is to monitor populations and identify prime breeding sites. Monitoring larval and adult populations is essential to accurately estimate the need for—and effectiveness of—control measures, and determining where you should concentrate your control efforts. Monitoring methods include:Landing counts, which record the number of adults that land on an unprotected arm over a certain period of timeLight traps that catch adult mosquitoesDip counts, which record the average number of larvae and pupae located on the surface of a body of water.
In Illinois, the Northwest Mosquito Abatement District (NWMAD) focuses most of its effort on annual surveys to locate, map, and inspect areas that foster mosquito production, said NWMAD Director Mike Szyska. “The topography of the district, which covers about 240 square miles of northwest Cook County, is quite diversified,” he said.
Mapping and identification of breeding sites is essential. “Our mosquito season is shorter than other areas of the country, but the intensity of mosquito development is significant,” said Jim Stark, public affairs coordinator for the Metropolitan Mosquito Control District (MMCD), which provides services to 2.7 million people in the Minneapolis-St. Paul area. This district is one of the largest by land size in the United States, and one of the best funded. “We also have a high density of wetlands in the area, including more than 50,000 identified areas in which mosquitoes develop, ranging from small areas such as freeway ditches to 100-acre swamps,” said Stark.
Step 3: Reduce the breeding sites or larval habitat. Because water is the critical element in mosquito development, managing standing-water sites is essential. Reducing breeding sites can be as simple as clearing a gutter or removing old tires, or as major as reworking landscaping and ditching in marshlands to improve drainage.Choose Your Weapons
Control programs once relied solely on targeting adult mosquitoes with products called adulticides. The best example of this is fogging, in existence since the 1940s and still a component of control programs. However, in recent years, there have been significant developments in products that reduce reliance on fogging by controlling mosquitoes before they become biting adults.
Biological methods of controlling mosquitoes also have been used with some success. However, there are logistical concerns with their use. The MMCD experimented with use of Gambusia affinis, a fish that feeds on larval mosquitoes. “Gambusia affinis are not a native species in Minnesota, and having to reintroduce them to areas that would completely dry down or freeze during the winter was not practical,” said Stark.
While the fish used in Minnesota can be an integrated component, the most commonly used products—larvicides—address the long term. The average female mosquito lays 200 eggs in her lifetime, so it only takes a few females missed by fogging to perpetuate the problem.