Mosquito General Information

The Responsibility for Mosquito Control

Everyone is responsible for eliminating and preventing mosquito breeding on their property. Chapter 111, Regulation 2 of the Maricopa County Health Code states:

All mosquitoes must have water to complete their life cycle. Stagnant water left from monsoon rains can increase mosquito activity. Rain and irrigation water can produce hundreds of thousands of mosquitoes if larva are allowed to stand as little as three days. In areas where ponding cannot be prevented, the water can be treated within 24 to 48 hours to kill the developing mosquitoes before the biting adults can start emerging. Here are a few tips from Maricopa County's Vector Control program on what you can do to eliminate mosquito breeding.
	Drain animal watering troughs, bird baths, pet watering dishes, etc. weekly.
	Repair water leaks, sprinkler systems or coolers that cause water to pond.
	Remove vegetation and floating debris in and around ponds and stagnant swimming pools to limit breeding potential. Also, you may want to consider adding mosquito-eating fish called gambusias. The fish are available free of charge from the Vector Control office. Just call at (602) 506-0700 to schedule a pickup time.
	Fill in low spots, control the irrigation in your yard or pastures, and drain standing water from buckets and other containers that can collect water on your property.

Mosquitoes in Maricopa County

Mosquitoes have a serious impact on the health, comfort, and economic welfare of people. Some species transmit diseases to man and animals.  In Maricopa County, there is particular concern with mosquito-borne encephalitis (sleeping sickness).   Large numbers of mosquitoes interfere with outdoor work and recreation, cause livestock to lose weight, and lower property values.

There are 2 main types of mosquitoes in Maricopa County:

1. STAGNANT WATER MOSQUITOES
   (Culex mosquitoes)
   • Importance
     

     Culex tarsalis: This is the most important mosquito of arboviruses in westrern North America. Responsible for maintenance , amplification and epidemic transmission of Western Equine, and St Louis viruses in irrigated and riparian habitats.  Also capable of transitting: Venezuelan Equine, Japanese Encephalitis, Murray Valley, West Nile and many others.  Larval habitat is usually among surface water pools that are frequently surrounded by grasses and annual vegetation and agricultural tail water. Larval development 7 days to 4 weeks depending on temperature and food supply.  Females feed mostly on birds shortly after sunset.  Flight range up to 17 miles.

     Culex quinquefasiatus: The southern house mosquito is found throughout the southern half of the United States. Its Latin name refers to five lines that can be seen on the length of the body. This mosquito prefers to lay eggs in small pools of water, and can utilize water that is polluted with organic material. This mosquito enters houses readily, hence its common name. It can be an annoying pest at night, not only because of its bite but also because of its high-pitched buzz. The southern house mosquito can transmit nematodes which cause dog heartworm and viruses causing encephalitis.

   • Typical Breeding Sites
     Tin cans, old tires, decorative ponds, bird baths, horse troughs, overgrown ditches, unmaintained swimming pools, open septic tanks, sewage and industrial waste ponds.
   • Breeding Site Selection
     Eggs are laid in cluster directly on the surface of standing water. Continuous reproduction cycles as long as water stands and conditions remain favorable.
   • Adult Habits
     Seldom seen in daytime, rests in shrubbery and other cool sheltered places. Active and biting during nighttime hours, indoors and out. Rests in open weeds and grass during daytime, but will rise up and bite if disturbed.


2. INTERMITTENT WATER MOSQUITOES (Flood water mosquitoes)
   • Importance

     Aedes vexans: One of the most widespread pest mosquitoes in the world. In North America, it is common in southern Canada and is found throughout the United States, with the exception of Hawaii. They are vicious biters and are responsible for most mosquito nuisance complaints. They are known vectors of Western Equine and St. Louis Encephalitis. They can also be vectors in dog heartworm.

     Psorophora columbiae: Also known as the Dark Ricefield Mosquito. The females are furious biters in day or night. Hosts include any warm blooded animal; however bovine blood seems to be preferred. Well documented studies of cattle have shown severe losses in weight gain and milk production resulting from the bloodfeeding activity of this mosquito. Certainly, Psorophora columbiae causes extreme annoyance to people. The mosquito is a known vector of encephalitis. It is a widespread pest from Florida, where it is known as the 'glades mosquito," to New York. Scattered populations exist across the United States westward to California. The species is found in Mexico, Central America, the Caribbean and South America to Argentina. Psorophora columbiae reaches its greatest abundance in the rice growing areas of the southwestern U. S. where astronomical numbers, similar in magnitude to the production of saltmarsh mosquitoes, may occur. Psorophora columbiae is a large dark mosquito with white or yellowish markings. The tarsi and proboscis are dark brown and banded with white scales. The hind femora have an apical white band and white knee spots. The first segment of the hind tarsus is brown with a white ring in the middle. The wings are speckled dark brown and white.

   • Typical Breeding Sites

     Irrigation or rainwater that ponds and stands for more than three days, such as over-irrigated or poorly leveled yards and pastures, tail-water ponds, desert ponds, stock tanks, backed up washes and flood control drainage areas.

   • Breeding Site Selection

     Eggs are laid on soil in areas where water has ponded, where they will lay dormant until flooded by water from the next rain or irrigation. Only one generation is produced per flooding.

   • Adult Habits

     Most active at sundown when they attack man and animals in swarms.

   AEDES AEGYPTI MOSQUITOES:

   An exotic species of mosquito known as Aedes aegypti has recently been found in Tempe. This mosquito, while not native to Arizona, has been spreading into many populated areas of southern Arizona. Aedes aegypti is capable of transmitting diseases such as dengue fever and yellow fever. This mosquito thrives in urban and suburban neighborhoods because backyard containers and clutter (tires, buckets, water cans, etc.) offer ideal breeding conditions for them.

   Life Cycle and Information on Aedes Aegypti Mosquitoes:

   Oviposition: Takes place in the afternoon in dark-colored water containing organic material (e.g., decaying leaves) in dark-colored containers with wide openings. Containers located in the shade are preferred. Females lay their eggs singly on the sides of the container at the water line in batches of 30-50. Egg laying occurs over a period of several days.

   Eggs: Exposure to high humidity at the water line for 2-3 days is required for larvae to hatch from their eggs. However, if the eggs dry out before this development period, they will collapse and the embryos will die. If they remain unhatched above the water line, and the level of humidity is sufficient to permit larval-embryo development, eggs become "cured." This means they are resistant to desiccation and can survive for upwards of six or more months. They can also survive short periods of subfreezing weather. Later, when exposed to water, the eggs will hatch within a day or perhaps even within minutes. The eggs do not all hatch with a single inundation, however. Instead, they hatch in progressively smaller numbers through a succession of inundations.

   Larvae: The 4 larval stages (instars) take 5-10 days for development (some texts say 5-7 days).

   Pupae: Transformation from the pupal stage to the adult stage generally takes 2-3 days. Under the most favorable climatic and environmental conditions, the entire immature or aquatic cycle (i.e., from egg to adult) can occur in as little as 10 days.

   Adults: The life span for adult mosquitoes is between 2 weeks to a month or more.

   Flight Range: Usually 50-100 meters. Ranges have also been expressed as 100 feet to 100 yards, and 25 to 500 yards. However, new studies are indicating that this mosquito may be capable of flying longer distances - as far as 850 meters or half a mile or so (see P. Reiter et al., "Short Report: Dispersal of Aedes Aegypti in an Urban Area After Blood Feeding as Demonstrated by Rubidium-Marked Eggs," American Journal of Tropical Medicine Hygiene 52(2):177-179, 1995).