Suborder Anoplura

These are the sucking lice. Adults are 0.5-3.0 mm long and have a somewhat flattened body; they are yellowish white to pale brown, and wingless. The head is conical, slender, and distinctfrom the thorax; the proboscis and sucking mouthparts project forward. The thorax is relatively small and fused; the legs are strongly developed, and have a one-segmented tarsus and a large claw. Immature stages are similar to the adults, but less sclerotized and with a reduced number of setae. These insects are obligate parasites ofmammals, and remain on the host during their entire life. Sucking lice are generally host-specific, and many are restricted to one animal species. There are several generations per year. Eggs are firmly attached to the hairs of the host, or in the case of Pediculus humanus, to the clothing of the host. The number of eggs per female is about 30. Eggs hatch in about 10 days and larval development is completed in about 20 days, depending on environmental conditions. The three nymph stages maintain contactwith the host. Food for the adults and immatures consists of blood of the host.

Legs end in a tibial thumb and tarsal claw, which adapt these insects to clinging on to hair or coarse fibers. The shape of the Pediculus claw has some epidemiological significance. In the USA the prevalence ofhead infestation of lice is 35 times higher among caucasians than among the black portion of the population. A major contributory factor is thoughtto be the adaptation of the claw to grasp to the predominant hair type in the host population. Caucasian hair is round in cross-section, whereas Afro-Caribbean hair is flattened oval. The claw ofPediculus may have difficulty grasping the hair ofnon-Caucasians. Coevolu-tion of lice and their mammal hosts is evident by the distribution and host-specificity of current species. Chimpanzees, New World (westernhemisphere) monkeys, gibbons, and great apes have a species of Pediculus, and gorillas have a separate species of pubic louse, Phthirus gorillae. It seems that the host preferences of these lice associated with primate hosts antedate the divergence of the ape and anthropoid stocks. The early domestication of the pig and its close association with humans is evident by the feeding habits of the sucking louse Haematopinus suis, which includes pig and humans.

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