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WESTERN MALARIA MOSQUITO
GENERAL INFORMATION | 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. | |
Adult Daily Activity: 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. | | |
Adult Flight Range: Adults have been known to travel up to ten miles from their breeding habitat. | | |
Adult Feeding: 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. | | |
Eggs and Larvae: 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. | | | | | | Hibernation: Females hibernate during the winter months and again disperse from their hibernating sites in February or March, becoming persistent biters for several weeks. | | | | | |
DISEASES TRANSMITTED Anopheline Mosquitoes are the only group of mosquitoes capable of transmitting malaria. Four species of Anopheles are found in California, but only two are considered
effective carriers of malaria, they are Anopheles freeborni and Anopheles punctipennis. Anopheles freeborni is currently considered to be the most important vector species. California has been virtually free of malaria due to intensive mosquito control activities and modern drugs which have suppressed this disease. However, malaria could be re-introduced into a local community by an individual returning from overseas with the malaria parasites in their bloodstream. In such an event, mosquito abatement and public health officials would take rapid action to prevent an epidemic.
California does have a few dozen introduced cases of malaria each year
(see California Department of Health Services,
Morbidity
Tables), Western Equine Encephalitis and St. Louis Encephalitis viruses have also been isolated from this species in nature. Economic losses due to the persistent biting habits of this species have been documented. Man's activities are often curtailed where large numbers of this mosquito are present. WESTERN MALARIA MOSQUITO LIFE CYCLE | Western Malaria Mosquitoes have four life stages: egg, larva, pupa, and adult. The first three stages of the Western Malaria mosquito (egg-larva-pupa) are spent in the water. The eggs hatch into larvae (wrigglers which then feed on small organic particles and micro-organisms in the water. Western Malaria Mosquito larvae are usually found lying parallel to and at the water's surface. The larval stage usually averages 15 days. 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 three days, during which time feeding does not occur. When the transformation is completed, the new adult splits the pupal skin and emerges. Under optimum conditions development from egg to adult takes about three weeks. However, all mosquito developmental times are dependent on the temperature
and nutrients of the water in which they develop. |
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CONTROL METHODS | | Where possible, the best approach is to prevent mosquitoes from breeding by eliminating or modifying the breeding sites. Techniques such as filling, pumping, ditching, draining, or reshaping of sources may be used. In some cases recirculation of the water is effective.
Close coordination with your local mosquito abatement district and
environmental regulatory authorities is recommended. |
RESIDENTS SHOULD | If you have a mosquito problem call your local Mosquito Abatement District to identify the problem. That is the first step in identifying what type of mosquito is being dealt with. | Use insect repellents if it is necessary when in an area where this mosquito is found. Read and follow the directions carefully! |
PERSONAL PROTECTION FROM MOSQUITOES | | FIRST AID FOR MOSQUITO BITES | q Reduce outdoor activities during peak feeding periods. | q Wash bite with soap and water. | q Wear long pants and long sleeved shirts. | q Apply anti-itch medication. | q Apply insect repellent. | q Apply cold cloth for swelling. | | q Watch for secondary infections. |
For more information on Western Malaria Mosquitoes contact: Napa County Mosquito Abatement District |
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