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Washino’s Willow Mosquito

Washino’s Willow Pool Mosquito (Aedes washinoi) is one of 53 types of mosquitoes that occur in California.  It is an aggressive day-biting mosquito commonly found breeding in shallow ground pools and riparian sites dominated by willow or cottonwood trees.  This species has also been found breeding in areas with dense blackberry thickets.

Diseases Transmitted

Washino’s Willow Pool Mosquito does occasionally create domestic, industrial and agricultural pest problems when they are present in large numbers. Although California Encephalitis virus has been isolated from natural populations of these mosquitoes, no confirmed human cases of mosquito-borne disease has been linked to this species of mosquito.

Life Cycle

Washino’s Willow Pool Mosquitoes have four life stages: egg, larva, pupa, and adult.  The immature stages need standing water to complete their life cycle.

After an adult female lays her eggs they hatch into larvae (wrigglers), which feed on small organic particles and microorganisms in the water.  Feeding occurs when they hang from the water’s surface by the tip of their tail (siphon) or by browsing along the bottom of their habitat.  Because they are air breathing organisms they must return to the water’s surface to breathe.

About one to two weeks are required for larval development.  At the end of the larval stage, the mosquito molts and becomes the aquatic pupa (tumbler).  The pupa is active only if disturbed, for this is the resting stage where the larval form is transformed into the adult.  This takes about two days during which time feeding does not occur.  When the transformation is completed, the new adult splits the pupal skin and emerges.

Adult Daily Activity

Adults emerge during late winter and early spring and can persist through early June.  Man-made canals and natural water ways have sometimes been used by these mosquitoes as a passage way into local human developments.

Adult Flight Range

Usually stay within one mile of their breeding site.  Maximum recorded flight range 1.5 miles.

Adult Feeding

Females tend to feed during the day and at dusk.  Their preferred hosts are humans and large mammals.

Eggs and Larvae

Eggs are laid in the muddy margins adjacent to the receding water line of the larval habitat and hatch the following winter when reflooded.  Larvae usually hatch during early winter after sufficient rainfall has filled their habitat with enough water to submerge the last season and prior seasons eggs.  Additional hatches of larvae can occur if late winter and early spring rains refill drying larval sites.  Larve of this mosquito also exhibit a late fourth instar diapause and partial synchronous adult emergence similar to that observed in the Winter Salt Marsh Mosquito (Aedes squamiger)