Mosquito Information

Pinal County Environmental Health's Vector Control Program maintains a specific focus on mosquito-borne disease prevention. We continually conduct mosquito monitoring throughout the county, looking for specific mosquito species that are competent vectors for human diseases such as West Nile Virus. We provide guidance to private residents, homeowners associations, business owners, and utilities to prevent mosquito breeding on their property. Our focus is on source reduction of mosquito breeding and biological control of mosquito populations where applicable. Further abatement activities, such as the application of larvicide or fogging for adult mosquitoes, may be considered if warranted via surveillance.

We recommend that individuals be prudent and protect themselves from mosquito bites. The first line of defense would be to avoid outdoor activities during times when mosquitoes are present. If being outdoors cannot be avoided, it is highly recommended that you wear pants and long sleeves and use an appropriate EPA-approved mosquito repellant.

People should be aware of the different types of mosquitoes and which ones are most likely to carry the West Nile virus. Mosquito abatement programs focus on those species of mosquitoes that cause disease.

Permanent (Stagnant) Water Mosquitoes

 Permanent (Stagnant) water mosquitoes are the most important vector for West Nile Virus:

  • These are found in places that hold water for long periods of time, such as stagnant ponds and abandoned green swimming pools. They are seldom seen in the daytime when they rest in shrubbery and other cool sheltered places. They are active and biting during nighttime hours, indoors and outdoors. Even though they are at rest during the daytime, they will rise up and bite if disturbed.
  • Common types of permanent water mosquitoes found in Pinal County include:
    • Culex tarsalis
      • This is the most important mosquito of arboviruses in western North America. Larval habitat is usually among surface water pools that are frequently surrounded by grasses and annual vegetation and agricultural tailwater
    • Culex quinquefasciatus
      • The southern house mosquito is found throughout the southern half of the United States. This mosquito prefers to lay eggs in small pools of water and can utilize water that is polluted with organic material

Floodwater (Intermittent Water) Mosquitoes

Floodwater (Intermittent Water) mosquitoes are nuisance mosquitoes. They are rarely infected with West Nile Virus, and they have not been deemed a public health threat:

  • Floodwater mosquitoes typically appear (sometimes in significant numbers) a couple of days after rains and flooding.
  • Monsoon rains and flood irrigation contribute to the floodwater mosquito population.
  • Common types of floodwater mosquitoes found in Pinal County include:
    • Psorophora columbiae
      • The females are furious biters day or night. Females lay their eggs on damp soil in depressions subject to flooding by rainfall. The larval period is relatively short, usually requiring 3 to 5 days. This mosquito can be found in areas with flat sheets of water, usually 3 to 6 inches deep. Psorophora columbiae prefers habitats with direct sunlight. She can be found in pastures, lawns, golf courses, and open fields.
    • Aedes vexans
      • Virtually any transient water can support Aedes vexans larvae, but rain pools in un-shaded areas produce the largest broods. The species is most common in grassy pools that border trees or shrubs. In most cases, floodwater habitats will be dominated by this abundant mid-season mosquito

View Arizona Mosquito Information (PDF) for more information on mosquitoes in Arizona.