Season by Season: How Mosquito Control Varies Across the U.S.

Changing weather patterns are stretching mosquito seasons and reshaping how mosquito abatement districts approach control throughout the year. The research organization Climate Central conducted a study of major US cities and regions to examine how shifting weather patterns have specifically affected the length of the mosquito season. The study assessed weather trends between 1979 and 2022, and found that 173 of 242 cities studied have a longer annual mosquito season, by an average of 16 more "mosquito days" – defined as those days having average relative humidity of 42% or higher and an average daily temperature range between 50 and 95 degrees.

As weather shifts continue to alter traditional mosquito timelines across the United States, mosquito abatement districts (MADs) and public health officials (PHOs) must stay flexible, proactive, and regionally focused. Seasonality now varies more dramatically from one region to the next, affecting everything from when to begin treatment to which products to apply.

Understanding your local mosquito season is the first step in creating an effective, community-specific control plan.

Regional Mosquito Patterns: What You Need to Know

Southern U.S. (e.g., Texas, Florida, Louisiana)

Warmer climates mean mosquito activity can begin as early as February and persist into late fall. For the Southeast in particular, the study estimated 218 total mosquito days in a given season, accounting for approximately 60% of the year. These regions often require year-round surveillance and treatment, with an emphasis on pre-treatment and long-residual larvicides to limit early-season outbreaks.

Midwest and Northeast (e.g., Illinois, New York, Pennsylvania)

Mosquito season typically begins in late spring and extends into September or October. According to the study, State College, Pennsylvania (33 more days) and Cleveland, Ohio (27 more days) are among the cities in these regions with the most significant growth in mosquito days per season. Increasing rainfall and warmer fall temperatures have extended the season, making mid-to-late season adulticide treatments more critical than ever.

Western U.S. (e.g., California, Arizona, Utah)

Among cities experiencing an increase in mosquito days, three of the top four are located in the Western U.S. Santa Maria, California, is first, with 43 more days, followed by San Francisco, which is second, with 42 more days, and Seattle-Tacoma, which is fourth, with 32 more days. While dry conditions can suppress some mosquito activity, irrigation and urban environments still present risks. Drought conditions can also increase the spread of disease as mosquitoes and hosts are concentrated around limited water sources. Surveillance is crucial for detecting early spikes, particularly following summer storms or periods of high heat.

Controlling Mosquitoes as Seasons Shift

With longer mosquito seasons and fluctuating climate conditions, a multi-phase control strategy is essential. The right larvicide, timed correctly, can provide pre-treatment flexibility and residual power to suppress mosquito populations across a variety of habitats.

Product Highlights:

Duplex-G™ Larvicide

  • As one of the most effective tools in combating mosquito larvae in both typical and post-storm conditions, Duplex-G™ delivers dual-active control through (S)-methoprene and Bti. Its Active Booster Release Technology offers quick knockdown and extended protection—making it ideal for both early and peak-season applications.
  • Whether you're planning for spring rainfall or responding to a late-summer disease spike, this product provides fast-acting and long-lasting results. It's also environmentally compatible and minimizes impact on non-target species—an important consideration for communities with sensitive ecosystems.

Altosid® P35

  • Altosid® P35 is a granular larvicide that provides up to 35 days of residual control in continuously wet conditions. With dual encapsulation technology and pre-treatment capabilities up to 15 days before flooding, it activates on contact with water to prevent adult mosquito emergence. Its uniform spherical design ensures smooth calibration and application by air or ground.
  • Ideal for flood-prone environments and extended wet seasons, Altosid® P35 offers reliable, long-lasting mosquito control when consistent water presence is a challenge. Its durable formulation helps ensure protection even in the most persistent breeding conditions.

Altosid XR-G® Ultra

  • Altosid XR-G® Ultra delivers up to 28 days of residual control using a clean, carbon-free (S)-methoprene granule. It's ideal for pre-treatment of floodwater habitats and is designed for easy, consistent application across crop and non-crop sites. Public health professionals trust this flexible, long-lasting solution for effective larval control.
  • Perfect for sites requiring clean, targeted applications, Altosid XR-G® Ultra is equipment-friendly and formulated for precision, helping districts cover broad areas efficiently without clogging or overapplying, especially valuable in sensitive or mixed-use environments.

Zenivex®

  • All Zenivex® mosquito adulticide formulations are ready-to-use for ground or aerial application, require no aquatic setbacks and have crop approval so you can spray throughout urban and rural settings.
  • Zenivex® E20 and Zenivex® E4 are ready-to-use fomulations as well as oil-dilutable for use in Ultra Low Volume (ULV) applications, while Aqua Zenivex™ E20 has the efficacy and positive toxicity profile of Zenivex® products, in a water-dilutable formulation.

The Reduced Risk Advantage

When mosquito populations get out of control, your community is at risk. That’s why Central Life Sciences created the Zenivex® product line, a trio of innovative solutions designed to help stop an outbreak in its tracks and protect the public health. These EPA classified reduced risk adulticides provide quick, permanent knockdown and reliable control of adult mosquito populations in any labeled mosquito habitat.

The Importance of Layered Control

Seasonality may vary, but one thing remains constant: the need for integrated mosquito management.

  • Maintain ongoing surveillance and community education to understand local mosquito population pressure and ensure a well-informed public
  • Begin with larvicide applications early in the season and continue them throughout the season
  • Include adulticide use mid-to-late season to address peak populations and disease risk

Stay Ready, Stay Regional

No two mosquito seasons are exactly alike. By tailoring your control efforts to your region's unique seasonality and using products from Central Life Sciences, MADs and PHOs can stay ahead of disease transmission and protect public health from spring through fall.

Do you need help selecting the right solution for your region? Contact a sales representative near you!