Structure and function of the cibarial armature in Simuliidae

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Abstract
Cibarial armature morphology in adult female blackflies (Diptera: Simuliidae) is described using scanning electron microscopy. Three distinct types of armature are recognized, comprising those with teeth, e.g. Simulium ochraceum, S. ornatum, S. veracruzanum and S. vorax, those with spicules, e.g. Austrosimulium bancrofti, S. damnosum, S. exiguum, S. metallicum and S. neavei; and those lacking these projections, e.g. Prosimulium rufipes and S. lineatum. Whereas the armature is poorly developed in vectors of human onchocerciasis such as S. damnosum, S. exiguum, S. metallicum and S. neavei, the well-developed armature in S. ochraceum, S. veracruzanum and S. vorax does not prevent these species becoming infected with Onchocerca spp. (Nematoda: Onchocercidae). Hence the armature is not primarily a mechanism to counteract microfilaria superinfection. Since cibarial armatures are more developed in the haematophagous females than in the males of certain Families of flies, e.g. Ceratopogonidae, Culicidae, Phlebotominae and Simuliidae in the sub-order Nematocera, evidently the armature has evolved in response to the blood-feeding habit. As the suction of imbibed blood by the cibarial pump may require a valve mechanism to prevent back-flow, it is suggested that the armature is primarily for this purpose. Secondarily, the cibarial armature presents a damaging barrier against ingested microfilariae.