Hamilton County environmental health director discusses managing mosquitoes

The onset of warm weather leads many to eagerly prepare for cookouts, pool parties, and other outdoor fun. However, every rose has its thorn, and such festivities are often accompanied by culcidae – the scientific name for mosquitoes. Hamilton County’s resident expert discusses how you can minimize and mitigate the Queen City’s ubiquitous summer pest.

Jeremy Hessel, the director of the environmental health division at Hamilton County’s Department of Public Health, has worked there for 25 years, beginning as a general inspector. The 13-employee department administers numerous public health functions, from examining its restaurants, pools, and other public facilities for code violations, as well as preventing infestations of pests such as mosquitoes.

According to Hessel, the general mosquito population has remained constant but can fluctuate based on annual variations in precipitation and temperature. Whenever there are greater opportunities for stagnant pools of water and warm, humid air, there’s an opportunity for mosquitoes to breed. He said he hadn’t read any research that specifically correlated climate change with an uptick in mosquito populations, but noted that any factors that would lengthen their breeding season, which typically spans from May to October, or rainfall would be likely to increase their presence.

“Rain can flush out stagnating bodies of water that reduces their population,” he said. “But, when rainy periods are prolonged over several days, it creates more opportunities for pools of water that give mosquitoes more chance to breed.”

Hessel said minimal stagnant water is needed to give mosquitoes a chance to thrive: “A bottlecap tossed on the sidewalk is enough for mosquitoes to produce their larvae.”

The red welts on the skin and the persistent itch that mosquito bites create are annoying, but they also carry the risk of transmitting the Zika and West Nile viruses, as well as encephalitis. According to data from the Ohio Department of Health (ODH), Hamilton County has averaged approximately 0.4 West Nile virus cases per 100,000 residents per year from 2002 to 2023, translating to about three cases on average per year during that period. Hamilton County wasn’t among the 10 counties that reported a total of 14 statewide West Nile incidents in 2024. ODH data indicated a statewide rate of 0.4 cases per 100,000 per year for the 22-year period, which would equate to between 40 and 50 reported annual cases, indicating a decline.

Prevention is important in minimizing mosquito-induced issues. Hessel said that they bite most aggressively during morning and afternoon hours. The Hamilton County Public Health Dept. recommends light-colored clothing with long sleeves and using an insect repellent containing DEET, Picardin, or other ingredients listed here.

To minimize the health risk around the home, Hessel’s department summarized its tips as "drain, dunk and protect."

• Drain: Eliminate standing water collecting in pools, birdbaths, playsets, wheelbarrows, old tires, gutters, and other vessels. Block mosquitoes from these areas by draining, sanitizing, filling, or covering them.
• Dunk: Buy larvicide or "dunks” to kill mosquito larvae in standing water that cannot be drained. These inexpensive, environmentally safe products kill mosquitoes before they become adults that fly and bite. They’re available as liquids, granules or briquets, and can be purchased in home improvement or hardware stores.
• Protect: Avoid being outside (pets too) during peak mosquito times (dusk and dawn), especially in humid spaces. Wear light-colored, loose-fitting clothing, and apply mosquito repellents. Install or repair door and window screens to keep the bugs outside.

Hessel’s department will respond to complaints of mosquito infestations by applying larvicide to large areas of standing water, but that eradicating adult mosquitoes was the domain of private contractors. He wasn’t sure of the exact formulation, but noted that they were developed to harm only mosquitoes without creating toxic residue that would impact other species or negatively affect nearby structures.

“The label is the law,” Hessel said. “It’s designed to not be harmful to plants or other animals, but a product has to be used in accordance with specs.”

He also mentioned gutters as another potential mosquito-breeding problem area that’s often overlooked. Gutters and downspouts clogged with leaves and debris will trap water and create a rich environment for their larvae to grow and hatch. Thus, he suggested cleaning them consistently during “skeeter” season.

In addition to protecting against mosquitoes, Hessel noted that the recommended repellent and loose clothing also protect against ticks and other biting pests, providing additional protection against pest-born illness.