AMES, IA – Despite a slow start following several dry years, mosquito populations in Iowa have ramped up this season, according to Ryan Smith, associate professor of plant pathology, entomology and microbiology at Iowa State University.
“Regular rains and flooding in some areas of the state are providing good breeding conditions much later into the summer,” he said.
Smith leads the Iowa Mosquito Surveillance Program, which has been running since the 1960s. It is one of the country’s most active, long-running programs, and one of the few led by an academic institution. Visitors to the surveillance program’s website can view mosquito population trends by year, by county, by the sites where traps are located and see the most often observed species. Currently, the program monitors about 100 traps in 15 counties.
Through July 31 of this year, 110,547 mosquitoes were counted in Iowa, with Polk and Black Hawk counties reporting the highest numbers. This is higher than the end-of-year totals for the past five years in the state (see graph). By comparison, during the wet year of 2018, 184,000 mosquitoes were counted over the season.
With mosquitoes on the rise, Smith advises the best defense is to avoid the insects, which are generally most active at dawn and dusk. If you are outside during those times, he encourages wearing protective clothing or using repellents.
A group effort
Trapping and identifying mosquito types is a group effort. A small cadre of Iowa State staff scientists and students working in Smith’s Lab count, sort and identify approximately 100,000 mosquitoes that are typical over the course of a season. They coordinate with partners in the Iowa Department of Health and Human Services (IDHHS) and its county health officials who lead trapping efforts, and the State Hygienic Laboratory at the University of Iowa, which tests a subset of mosquitoes (Culex species) for West Nile virus (WNV). Funding for the program comes from IDHHS through allocations from the Centers for Disease Control and Prevention.
The mosquito surveillance program uses different types of traps, depending on a variety of factors. The most frequently used New Jersey Light traps that monitor mosquito abundance also catch other bugs, and thus, require painstaking sorting. Other traps, such as CDC light traps or gravid traps, respectively, require dry ice or water-based attractants to better target mosquitoes and preserve them in a condition that enables easier identification and WNV testing.
“The program is important to help track mosquitoes in the state, their abundance and where they are found, which can be valuable for our understanding of the seasonal risks of mosquito-borne disease transmission,” Smith said.
The information collected helps guide a variety of public health responses that include working with homeowners in an area to reduce attractive breeding locations and guiding use of insecticide treatments and public health advisories about hot spots where extra precautions should be taken to avoid mosquitoes.
55+ types of mosquitoes
More than 50 types of mosquitoes have been found in Iowa. Some carry disease. Others don’t. Mosquitoes most often prey on birds and other wildlife or even livestock, with females sucking blood needed to produce eggs. When mosquitoes bite humans, they sometimes transmit diseases in the process.
Fortunately for Iowans, the state’s most common mosquito, Aedes vexans, is not a carrier of human disease. Species that pose more risks to humans include types of Aedes and Culex mosquitoes that can carry West Nile virus or other mosquito-borne diseases. WNV can be deadly to a small percentage of those exposed, especially the elderly or those with compromised immune systems. Fortunately, most people who contract WNV will experience mild or no symptoms, so its occurrence is likely underreported, according to Smith.
Thus far in 2024, 19 mosquito samples have tested positive for WNV, and one human case reported (in Harrison County). In 2023, 96 mosquito samples tested positive for WNV, and 17 human cases were identified.
“This year, we’re finding relatively high numbers of Culex tarsalis, typically found in agricultural and irrigated areas. Their presence can really be a problem, especially in northwest Iowa, a known hot spot for this type of WNV-carrying mosquito,” Smith said.
Some years, Iowa’s mosquito tracking program looks for specific species -- often coordinated with national tracking efforts.
That includes studying native Anopheles species, which have the potential to transmit malaria. A new report in the Journal of Medical Entomology, co-authored by Smith and colleagues Christopher Lee and Mark Leonard in the Department of Plant Pathology, Entomology and Microbiology at Iowa State, reports on the abundance and dynamics of Anopheles species in Iowa over the last 20 years to provide insights on the implications for public health.
A 2022 paper by Smith and others in Scientific Reports reported on the spread of the invasive Aedes albopictus mosquito known to carry Zika virus. The team concluded the mosquito is becoming established in Iowa due to warmer winter temperatures.
Though occurrences of both malaria and Zika so far in the state are travel-related, resulting from infections acquired in regions where the diseases are more widespread, the presence of these mosquito species increases the potential for future public health risks.
To learn more about the state’s mosquito tracking program and see examples of traps used for monitoring, watch this video, created by the College of Agriculture and Life Sciences at Iowa State and Iowa State University Extension and Outreach.
Contacts
Ryan Smith, Department of Plant Pathology and Entomology, 515-294-8828, smithr@iastate.edu
Ann Y. Robinson, Agriculture and Life Sciences Communications, 515-294-3066, ayr@iastate.edu