Scanning electron microscopic observation of the pretarsal suckers of the honey-bee ectoparasite,Varroa jacobsoni (Gamasida: Dermanyssina)

The pretarsus of the female miteVarroa jacobsoni Oudemans (1904) consists of two main parts, a cuticular basal stalk and an extrudable, membranous ambulacral pad, the caruncle. The caruncle, when fully extruded and expanded, becomes a bilobed sucker, and when deflated, the entire caruncle is retracted into the basal stalk. The basal stalk of the pretarsus with the sucker fully retracted into it resembles an inverted cone with its narrow portion attached to the apex of the tarsus. The basal stalk consists of three large plates; two lateral and one median. The proximal end of each lateral plate bears a sclerotized claw-like structure which functions to support the expanded caruncle. The median plate possesses a long, narrow ridge process connecting the basal stalk with the caruncle, and functions to control retraction and protraction of the caruncle. The morphology and function of the basal stalk suggest that the claw-like structure are the ungues; the median plate is the unguifer, and the median ridge is the tendon of the retractor/depressor muscles of the pretarsus. The significance of the pretarsal suckers to the control of the mite is also discussed.