"Mosquitoes may be an annoyance, particularly in wet years. But they are a part of the natural environment and a food source for a variety of other animals," said Jim Leach, a U.S. Fish and Wildlife Service refuge supervisor who oversees National Wildlife Refuge activities in Indiana, Ohio, Michigan and Wisconsin. "More importantly, the insecticides currently used to control mosquitoes can have a devastating impact on other insects, particularly aquatic insects, which are utilized by fish, amphibians and aquatic birds like ducklings as important food sources."
Because National Wildlife Refuge managers strive to manage their refuges as naturally as possible, Midwestern refuge policies do not allow the use of mosquito treatments on refuge lands except in cases involving threats to human health, such as the transmission of a mosquito-borne illness. Even so, refuge managers still cooperate with local mosquito control authorities to monitor mosquito populations on refuge lands. Managers also take on the annual chore of removing old tires, barrels and other debris deposited on refuge lands by high spring water levels and runoff from adjacent private lands. Such debris may serve as artificial breeding sites for "container breeding" mosquito species, many of which are potential carriers of human disease.
It can be difficult to identify one mosquito from another, but for scientists, species identification is an important distinction. While there are many different species of mosquitoes, relatively few actually have the potential to transmit disease to humans. Of the mosquito species which plague Midwesterners, research indicates that the treehole or container-breeding mosquito (Ochlerotatus triseriatus) is most likely to transmit LaCrosse encephalitis, a rare but potentially fatal disease which has been found in the Midwest.
Many species of mosquitoes targeted for control by local mosquito abatement agencies (through the application of insecticides, most commonly methoprene and Bacillus thuringiensis israelensis (Bti)) are not known to be carriers of human disease. But controlling even these nuisance mosquitoes does carry a biological price.
A multi-year scientific study conducted in Minnesota found the use of methoprene and Bti significantly reduced non-target aquatic insect populations along with mosquitoes. Additionally, questions on the long-term impact of these pesticides on aquatic birds such as ducks and other marsh birds remain unanswered. For these reasons, federal wildlife officials hesitate to implement chemical mosquito control measures on refuges; opting instead to take a conservative approach, with an eye toward the long-term health of these public lands.
"In cases where refuge or waterfowl production lands are contributing to a human health threat, we will certainly work with local officials to do whatever is necessary to address that threat," said Leach, adding there is no evidence refuge lands pose any greater threat to human health than other wetlands. "But lacking human health concerns, were going to let the natural processes at work on refuge lands continue without human intervention."
Despite the buggy forecast, Leach encourages potential refuge visitors to take advantage of spring and summer activities offered at National Wildlife Refuges. "Spring is one of the best times for wildlife viewing, especially for migratory birds and young mammals, " he said.
To minimize mosquito annoyance, refuge officials advise visitors to wear long-sleeved shirts and pants and apply insect repellent before venturing into areas where mosquitoes may occur.
