The Western Malaria Mosquito (Anopheles freeborni) is one of 53 types of mosquitoes that occur in California. It is the primary vector of malaria in the Western United States. It is also sometimes called a rice mosquito because it often develops in the water of rice fields.
This species is a medium-sized mosquito with dull brown to black coloration. The two sense organs on the head of the female, known as the palpi, are about as long as the proboscis (beak) and give the appearance of a head with three beaks. The outer half of the wings have four to five spots which are easily seen with the naked eye. Males resemble the females, but have bushy antennae, and claspers on the tip of their abdomen.
This species occurs in the Western United States north to Southwestern Canada and south into Mexico. It extends to the southeast as far as El Paso, Texas, but is probably most abundant in the great Central Valley of California. It has been found from elevations below sea level and as high as 7,000 feet.
The adult population reaches its peak in August and September. During the fall, Western Malaria Mosquitoes undergo a unique biological behavior in preparation for hibernation. In the central valley, large numbers of adults congregate in open shelters in September and later disperse in a fall migratory flight. Migrating adults have been found in communities up to five miles from their point of origin. A segment of the population also migrates as far as ten miles into the adjacent foothills up to an elevation of about 400 feet. The females are most active at dusk and will readily enter houses.
Adults have been known to travel up to ten miles from their breeding habitat.
Adult males do not bite, but feed on plant juices and nectar. Females may also feed on plant juices, but usually must have a blood meal in order to develop their eggs. Preferred hosts are large mammals, although this mosquito will readily bite humans when given the opportunity.
An adult female lays about 200 eggs, individually, on the surface of the water which float until they hatch in about two days. The female usually seeks out clear pools in full sunlight with emergent vegetation and/or green algae for laying her eggs. Sources include rice fields, rainwater pools, margins of lakes and streams, grassy irrigation ditches, agricultural tail-water ditches, and farm pond reservoirs.
Females hibernate during the winter months and again disperse from their hibernating sites in February or March, becoming persistent biters for several weeks.