Glossina species are tan or brown flies which range in length from 6 to 14 mm, excluding the proboscis. Members of the fusca group, which is considered phylogeneti-cally primitive, are the largest, being 9.5—14 mm long. The palpalis and morsitans group species are small to medium in size, about 6.5—11 mm long. Species in the palpalis group generally have a uniformly dark brown abdominal tergum, and the dorsal aspect of each hind tarsal segment is dark brown or black. Species in the morsitans group usually have dark segmental bands on the abdomen, and only the distal segments of the hind tarsi are darkened dorsally.

Tsetse adults are characterized by several distinctive morphological features. These include the shape of the proboscis, the position and branching of the fringe on the arista of their antenna, and the wing venation and folding pattern. The swollen, bulbous base of the proboscis that lies under the head is very different from the angled and thinner bases of the proboscises of the Stomoxyini. When the fly is not feeding, the proboscis extends directly forward between the palps in front of the head (Fig. 15.1). The proboscis (Fig. 15.3) is composed of two elongate, stylet-like mouthparts: the labrum and hypopharynx. The stylets are protected ventrally by the labium. The labellum at the tip of the labium is armed with teeth for cutting into host skin. The labrum, bounded by the hypopharynx and the labium, forms the food canal through which blood is drawn as the fly feeds (Fig. 15.3). The hypopharynx has a hollow central portion that forms the salivary canal through which saliva is secreted into the feeding site.

The three-segmented antennae arise on the frons, just below the ptilinal suture, as in muscoid flies. The first segment is very small; the second is at least 2—4 times larger than the first and generally about as long as wide; the third is very elongately oval to pea pod—shaped and bears the distinctive arista. The arista has a conspicuous fringe of hairs along its dorsal surface, and these hairs have small branch hairs, which are not found on any other aristate fly (Fig. 15.4). The large brown or reddish eyes are separated

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