Mechanics of blood-feeding in black flies (Diptera, simuliidae)

The structure and interrelationships of the mouthparts and of the food canal and its accessory cephalic structures of the females of Simulium venustum are described through microscopic observations. The mouthparts that enter the would during feeding are the mandibles, maxillary laciniae, hypopharynx, and labrum and collectively form a "syntrophium." The labium and labellar lobes, which do not enter the wound, ensheathe the syntrophium distally and must be retracted to allow biting. We present an interpretation of mouthpart function during biting that emphasizes how biting steps are accomplished and what sensory structures are used to monitor the process. Four phases of biting are identified: (1) initial penetration of the skin effected by the mandibles; (2) consolidation of mouthpart position involving anchoring the syntrophium into the wound by means of the barbed laciniae; (3) diet sampling and active feeding-food (blood) is pumped by three groups of muscles forming two functional pumps, one located in the cibarium, the other in the pharynx. These pumps are separated from each other and from surrounding regions of the food canal by valve muscles making the pumping process a complex and highly coordinated series of muscular contractions; and (4) mouthpart disengagement involving removal of the laciniae, thus releasing the syntrophium from the wound.