Mosquito Taxonomy and Species Complexes

In malaria entomology, anopheline species are grouped according to morphological criteria and related taxonomic information. Much of modern-day taxonomy addresses problems associated with species complexes, that is groups of morphologically indistinguishable species that are genetically different and that may differ greatly in vectorial potential. The limits of the traditional morphological approaches to species identification became apparent in Europe with the puzzling observation of “anophelism without malaria”: certain areas with low densities of An. maculipennis had malaria transmission, while other areas with an abundance of An. maculipennis had no malaria transmission at all. This observation subsequently led to the discovery of the An. maculipennis complex.

There are more than 20 recognized species complexes in the genus Anopheles, many of which include malaria vectors (Coluzzi, 1988). A variety of methods are available for discriminating among species—the gold standard relies on cytogenetics—but none are simple or as yet, practical for routine use in the field.

The identification of vectors that belong to species complexes has long been a stumbling block in malaria epidemiology and control. The failure to recognize sibling species can mean that vector species are mistaken for nonvector species, and vice versa. The results of field studies that evaluate larval ecology, seasonal biting rates, host preference, infection rates, resting habits, and malaria control efforts may be misleading if morphologically defined “species” actually are a mixture of two or three species. In Africa, for example, sibling mosquito species living in the same area respond differently to insecticides, presenting formidable obstacles to vector control operations.

Parasite Transmission

There are distinct groups of mosquito vectors associated with almost every major type of malaria (see Chapter 10). Very often, the single greatest source of variation within these regions is the mosquito itself. The variation among species, feeding habits, seasonality, abundance, and vectorial capacity all help determine how malaria is transmitted to and expressed in individuals and populations.

Field Studies

The principles and methods used for sampling anopheline mosquitoes have been the same for the past 25 years, and are described in detail by the

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