Mosquito of the Month: Anopheles quadrimaculatus – Common Malaria Mosquito

Malaria was eliminated from the United States by 1951. Elimination means it is gone, right? Forever? Well, not exactly.

Also known as the Common Malaria Mosquito, Anopheles quadrimaculatus is distributed throughout the eastern United States, often occurring in huge numbers in the southeastern states, especially along the Gulf of Mexico. This fact reinforces the importance of strong surveillance and disease testing programs in areas where the species inhabits. It is not unusual for VDCI’s surveillance traps set in the Mississippi Delta region to collect over 7,000 mosquitoes in one night, of which 99% are likely to be this species.

Female Anopheles mosquitoes lay their eggs individually on the surface of freshwater pools, preferring ponds and lakes with large amounts of vegetation, including rice fields. The eggs have floats on each side, keeping them on the water’s surface. Larvae hatch out usually within two or three days. Unlike the mosquito species previously featured in this series, Anopheles larvae lack a breathing siphon at the end of their abdomen. They rest parallel to the water’s surface and take in oxygen through palmate hairs along the abdomen. Like other mosquitoes, the pupae are active but do not feed. The entire life cycle – from egg to larva to pupa to adult – can take as little as five days when temperatures are warm mid-season, but usually requires one to two weeks for development. Adults usually live for a couple of weeks.

For a mosquito with such a deadly history for humans in North America, it is a rather frail species, with long spindly legs and a thin body. The species name, quadrimaculatus, means “four-spotted” in Latin, referring to the pattern of scales on their wings that cluster into four distinct patches, easily visible without magnification. Genetic studies have determined that this is actually a species complex – a group of at least five species that are genetically distinct, but similar enough in appearance that we cannot tell them apart morphologically with a standard dissecting microscope. Apparently, they can tell each other apart, but we do not know exactly how.

So, with such high numbers of Common Malaria Mosquitoes in some parts of the U.S., why isn’t malaria a more common vector-borne disease here? There are probably many reasons. First, a person with the Plasmodium parasite must be bitten by an Anopheles mosquito. Then, the mosquito needs to live long enough for the parasite to develop into an infective stage. Finally, the mosquito needs to bite another human to pass the parasite along. In many parts of the country where these mosquitoes are common, most houses have screened windows and many are air-conditioned. Many communities also have large-scale mosquito surveillance and control programs in place to reduce the populations to levels where disease transmission is less likely. Small localized transmission could occur, but large-scale epidemics are much less likely today.