DES MOINES — The city of Des Moines has discontinued its mosquito spraying, monitoring, testing and complaint hotline over budget concerns as the Iowa State Mosquito Surveillance program reports the lowest mosquito numbers in a decade across the state. Mosquito numbers are expected to rise due to recent heavy rainfall and flooding, the surveillance program said.

Ryan Smith, the principal investigator at the Iowa State Mosquito Surveillance program and an associate professor in the ISU Department of Entomology, said the current trap recordings are the lowest since 2016. The program operates approximately 100 mosquito traps across the state and has captured about 12,000 mosquitoes so far this season. In previous years, traps had captured 100,000 mosquitoes by this point in the season, and Iowa State University data attributes the decline to a dry spring.

Smith said it was somewhat surprising to see such low numbers this late in the season, noting that in some past years, more than 100,000 mosquitoes had already been collected by now.

Recent extreme weather now points in the other direction. Smith said flooding creates stagnant water where dormant eggs laid during earlier flooding events can hatch when water levels rise again. He explained that any kind of flooding does create stagnant water, and some of these mosquitoes will actually lie dormant in some of these areas that were laid maybe the last time when there was some flooding, and so the next time that water level rises again, these mosquito eggs can actually hatch out. He added that given the significant rain that had occurred and the amount of standing water, there was likely to be an increase in mosquitoes in the next week or so.

As the state-level numbers remain low, the city of Des Moines has pulled back its own local mosquito program. Budget concerns led the city to stop spraying for mosquitoes, discontinue monitoring and testing of the local mosquito population, and shut down the hotline for mosquito-related complaints. According to the city of Des Moines website, mosquito control spray has no residual effect and only kills mosquitoes on contact, and mosquitoes tend to return 24 to 48 hours after spraying. Unreliable weather conditions can also affect how well spraying works, and the spray does not prevent mosquitoes from breeding even under perfect conditions.

Within the region, Polk County Public Works performs mosquito spraying on an as-needed basis. Mosquito repellent remains recommended in sprayed spaces, especially in the early morning and late evening. Residents are advised to clear gutters and drain sources of stagnant water, such as old tires and rainwater receptacles, and to change water in birdbaths and pet dishes every two days to prevent them from becoming breeding grounds.

For homeowners seeking additional control, several treatment types exist. Barrier mosquito treatments involve applying chemical treatments directly onto surfaces to form a protective barrier, killing adult mosquitoes on contact and lasting two to four weeks. Larvicide treatments target mosquito larvae in standing water using bacteria to stop them from hatching; those treatments typically last about 30 days and work only in standing water. Mosquito misting systems spray insecticide mist at scheduled times, often targeting dawn or dusk emergence.

The pause in Des Moines comes as the state's surveillance network documents historically low mosquito activity — roughly 12,000 mosquitoes across 100 traps, compared with 100,000 by this point in prior years. With recent flooding now expected to drive an increase in mosquitoes, the absence of city-level monitoring and a public complaint hotline means the local program will not track where populations are rebounding or test for viruses.

Beyond Iowa, a bill was introduced in the New York State Legislature this session to lay the groundwork for comprehensive mosquito surveillance, reflecting broader questions about how municipalities fund and maintain monitoring programs as budgets tighten.