Shannon Fiecke of the Shakopee Valley News reports:

Minnesota’s No. 1 pest isn’t visiting us quite as early as usual, but it will be arriving in greater numbers.

The cold, wet weather the state has brought both bad and good news for mosquito season. While it has created a great deal of breeding ground for mosquitoes to grow the cool temperature has also slowed the larvae development process, providing a greater window for larvae to be killed before they can hatch into adults.

“We have had a cool spring and a pretty wet spring — and it’s not over yet,” said Mike McLean, a public information officer with the Metropolitan Mosquito Control District. “With these rains, the ground is getting fairly saturated, we’re starting to see some good production.”

Most years, mosquitoes have begun appearing in large numbers by about Memorial Day, but the metropolitan area is probably a week to 10 days behind, with significant hatches coming in recent days.

People will notice a greater abundance of mosquitoes this season, but it will actually be more of a return to normal. The last two to three years were pretty dry, McLean said, which kept the population low.

Warm days last May sped larvae growth, whereas the cooler weather this year has given the district a longer period to treat larvae before they can hatch.

The district’s starts the eradication process by dropping granules or pellets that contain a natural soil bacterium or growth regulator into waterlogged areas, such as wetlands and roadside ditches, either by helicopter or foot. The bio-rational control materials specifically disrupt the growth of mosquito larvae, and are said to pose no risk to human or animal health.

By treating larvae, the district estimates it reduces the adult mosquito population by about 75 percent, McLean said. The district focuses on areas known to harbor human-biting mosquitoes, targeting about 14 of 50 species found in Minnesota.

Once mosquitoes do hatch, the district treats areas with forms of Pyrethroid, a material similar to a natural botanical insecticide that has a low toxicity to mammals (including humans), but a great toxicity to certain insects and bees.

The same group of chemicals is found in dog-flea collars and is used to treat children’s head lice, McLean said.

The adult-control material is released in two different forms, either being transported by truck of backpack.

An aerial mist is released by truck in neighborhoods at dusk during certain weather conditions, when mosquitoes will be at their peak appearance. The fine fog is fast-acting but short-lived, only killing mosquitoes present at the time.

While the material sprayed isn’t terribly toxic to humans, the district still encourages people to close windows when they hear trucks roaming the streets.

The district is careful where it sprays, keeping a registry of hives and establishing setbacks from waterways because the chemical can also hurt fish.

Another form of Pyrethroid, called Permethrin, is applied by foot in targeted areas, such as the edges of parks or ball fields that are surrounded by woods. The oil-like substance is applied to vegetation, sort of like paint, killing mosquitoes on contact, and also acting as a long-term barrier, repelling future mosquitoes.

The district takes requests for mosquito control from both individuals and organizations, prioritizing treatment for big public events, but also considering areas that have generated lots of complaints. McLean said.

While the district focuses on treating areas that will provide the most benefit to the public, individuals can also hire private companies to treat their own property.

McLean cautioned people to make sure their contractor is licensed through the state Department of Agriculture, or, if property owners apply their own insecticide, to carefully read the product label.

JAPANESE MOSQUITO

Last year, the district announced it had found larvae of the Japanese rock pool mosquito in northern Scott County. The nonnative species is capable of transmitting the West Nile virus and encephalitis. The farthest north the mosquito was spotted before was central Michigan.
It appears efforts to get rid of the mosquito in Scott County were successful, as there have not been any larvae or adults found since in the area; however, larvae has been discovered in an area of Dakota County.

"This is fairly typical of what other communities in other parts of the country have experienced," McLean said. “You find it one year, get rid of it; it pops up somewhere else the next year, you get rid of it. Pretty soon it starts coming in more places than anyone can handle, and then it's established."

This was the pattern in Iowa.

“Minnesota is not out of its habitat range,” he said.

Shannon Fiecke is a staff writer for the Shakopee Valley News. She can be reached at sfiecke@swpub.com.