Anatomy of membranous mouthpart cuticles and their roles in feeding in black flies (Diptera: Simuliidae)

Abstract The nature and extent of the cuticular membranes of the mouthparts of females of Simuiium venustum are described. These membranes are arranged into four groups: (1) cuticular membranes of the labium/hypopharynx; (2) membranes of the apical labrum; (3) those of basal portions of the mandibles and laciniae; and (4) the labral flaps within the syntrophial food canal. From their external and internal structure it is concluded that membranes of the first three groups go through inflation/deflation cycles directly related to the food‐pumping rhythm. It is further concluded that these membranes line the inner and outer syntrophial and proboscis surfaces, acting as pressure seals both to prevent blood loss from the wound and air entry into the food canal during feeding. The labral flaps within the food canal appear to act as one‐way valves, keeping blood from leaking out between the mouthparts during the pumping downstroke but allowing pooled blood to enter during the upstroke.