Morphology

Triatomines range in length from 5 to 45 mm, with the majority of species falling in the range of 2028 mm. Most species are black or dark brown, often with contrasting patterns of yellow, orange, or red, notably on the connexivum (the prominent abdominal margin at the junction of the dorsal and ventral plates) (Fig. 5.2).

The head of an adult triatomine is constricted posteriorly to form a distinct neck behind the paired ocelli. Prominent hemispherical compound eyes are situated just in front of the ocelli. The region in front of the eyes is cylindrical to conical, hence the name "cone-nosed" bugs. The antennae are filiform and four-segmented. The beak, or rostrum, is three-segmented and is formed by the labium, which encloses the stylet-like mouthparts. These stylets are modified portions of the maxillae and mandibles that lie within a dorsal channel of the rostrum and are grooved to form a food canal and a salivary canal. When the bug is not feeding, the straight rostrum is held under, and nearly parallel to, the head (Fig. 5.3). In many nontriatomine reduviids, the rostrum is curved and strongly sclerotized.

The dorsal portions of the thorax include a collar, or neck, a somewhat triangular pronotum, and a scutellum. The undersurface of the pro thorax (prosternum) has a stridulatory groove that has fine transverse sculpturing. When the tip of the rostrum is moved anteriorly to posteriorly in this groove, sound is produced, the function of which is mainly defensive.

The fore wings, or hemelytra, have a leathery basal portion (corium and base of the clavus) and an apical membranous portion (apical clavus and membrane) typical of most heteropterans. The membrane is dusky in most species, but it may be spotted or darkened only along the wing veins. The wing veins of the membrane form two elongated closed cells. The hind wings are completely membranous (Fig. 5.1). The hind wings are rarely absent but may be greatiy shortened in some species. The relatively slender legs are used for walking. In addition to paired simple claws on each tarsus that allow the bug to crawl over rough surfaces, many species have a spongy structure, the fossula, at the apex of the tibia on one or more pairs of legs. The fossu-lae have adhesive setae on their surfaces that enable the bugs to climb on smooth surfaces, such as leaves and glass.

The triatomine abdomen is 11 -segmented, often pointed or lobed in the female, but smoothly rounded in the male. In many species, around the periphery of the abdomen, both dorsally and ventrally, are segmental plates (connexival plates) connected to the abdominal segments by intersegmental membranes. These membranes allow for expansion of the abdomen during engorgement. The membranes in different species are folded on themselves in various ways, allowing the plates and membranes to expand in accordion fashion during feeding.

Major Triatomine Vectors of Trypanosoma- cruzi and Their Geographic Distribution

Species

Geographic range

Rhodnius prolixus

Southern Mexico, Guatemala, El Salvador, Honduras, Nicaragua,

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