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.

Larvicides—which kill mosquitoes before they can develop into biting, breeding adults—comprise the preferred method for preventing future problems and health risks. Stark estimates the MMCD devotes 85% of its resources to larviciding; Szyska estimates 90% of his district's resources are spent on larviciding.

For any larviciding program to be successful, problem breeding sites must be identified and treated. Larvicides such as Altosid, from Schaumburg, Ill.-based Wellmark International, come in several forms to meet specific needs, such as larval habitat, manpower and equipment availabilities, and budget:

  • Briquettes and ingots provide consistent, slow-release control to areas where constant maintenance is impractical, such as catch basins, woodland pools, animal drinking troughs, retention basins, and roadside ditches. They may be hand-applied by operators on foot or from moving vehicles (saving time and money), and they come in two residual lengths, offering as much as 150 days of control.
  • Liquids come in two concentrations. They are ideal for synchronous broods of mosquitoes that commonly occur in a flood-water habitat, such as tidal marsh and retention overflow. They can also be used to make a sand granule for sites that contain heavy vegetation.
  • Pellets offer slow-dissolving, extended control (up to 30 days) for hard-to-treat sites such as marshes, rice fields, mangrove swamps, tire piles, ditches, and other water-holding containers.
  • Granules are ideal for large tracts of land, such as pastures and salt marsh. The small particle size ensures even distribution, but granules also lend themselves to treating small pockets of water common around households such as birdbaths and gutters.
  • The NWMAD employs college students each summer to distribute larvicides in backyard catch basins, sewer grates, flood-water areas, residential areas with standing water, ditches, and culverts. “We use Altosid pellets, ingots, and briquettes because of their residual and long-lasting control, which saves money, labor costs, and continues to provide control even after our summer crews depart to go back to school,” said Szyska.

    Start Talking

    Stark and his MMCD colleagues work closely with the local public works officials to share resources for mapping, cleaning, treating, and working to control the local mosquito population. “Currently MMCD provides all the control, but we hope in the future public works staffs may be able to assist with some treatments,” he said. “This may be most important in areas that are difficult to access, or may even be under lock and key. It's all about making the best use of public resources.”

    District and local public works officials have established a dialogue regarding mosquito control. For example, the district delays larviciding efforts until after the city cleans its catch basins. If the city plans road construction or other activities that would block access to catch basins, the district schedules treatments prior to road closures. “The dialogue is important, because West Nile virus won't go away,” said Stark.

    — VanGundy is an entomologist with Wellmark International.

    For more information, visit the American Mosquito Control Association Web site at