The Anopheles mosquitoes are one of about 41 genera of mosquitoes that occur worldwide. Of the nearly 3,500 mosquito species, about 430 are Anopheles. The only country or region that does not have Anopheles mosquitoes is Antarctica. Anopheles mosquitoes complete four distinctly different stages during their development – egg, larva, pupa and adult. The egg, larval and pupal stages take place in water while the adult stage is able to fly and move to other locations.
Adult female mosquitoes lay about 50 to 200 eggs at a time. Unlike other mosquito species who lay eggs in groups that are “glued” together (egg rafts), Anopheles eggs are laid individually and float on surface of the water. Eggs may hatch within 2–3 days after being laid but can take up to three weeks in cooler climates. The larvae get air through special organs on their body and must come to the water’s surface to breathe. Larvae spend much of their time feeding on algae, bacteria and other aquatic microorganisms. Once the larvae have completed four instars (stages), the pupae develop. Pupae also must go to the surface of the water and breath through a pair of organs known as respiratory trumpets. After about 2-3 days, the pupal stage is completed and the adult mosquito emerges.
Anopheles adult males obtain their nourishment from plant nectar and other sources of sugar. Adult females also feed on sugars, but must take a blood meal before they can produce fully developed eggs. After taking a blood meal, the female will find a protected resting site and wait until she can digest the blood and for her eggs to fully develop. When ready, she will lay her eggs on a water source and fly away to search out another blood meal.
While Anopheles mosquitoes look like other mosquitoes, there are four easy to see differences between Anopheles and other mosquitoes. First, the Anopheles mosquitoes have a pair of mouthpart palps that are about the same length as the proboscis. Second, the female Anopheles mosquito lays individual eggs on the water’s surface, not egg rafts. Third, Anopheles mosquito larvae orient their body parallel to the water’s surface when taking in air, unlike others who orient more or less perpendicular to the water’s surface. Fourth, Anopheles female adults position themselves at about a 45 degree angle to the host’s skin when taking a blood meal, unlike most other mosquitoes that assume more of a parallel position with the host’s skin when feeding.
Anopheles mosquitoes are one of the most important disease vectors among the insect world, earning this reputation as the result of being vectors of malaria. Worldwide, malaria deaths number up to about 1 million each year. Malaria mainly arises in lesser-developed tropical and subtropical parts of the world, and most of those who die are young children who have not yet developed immunity to malaria and pregnant women whose immunity heath in general is compromised by their pregnancy. While malaria takes “center stage” when it comes to disease transmission, anopheles mosquitoes may also transmit filariasis and some arboviral diseases.
Each year small numbers of malaria are reported in the United States. These cases primarily result from travellers returning to the U.S. from malaria endemic areas of the world. However, there is a risk for malaria to re-emerge in our country due to the abundance of competent Anopheles vectors, especially in the South.