Observations on the honey bee tracheal mite Acarapis woodi (Acari: Tarsonemidae) using low-temperature scanning electron microscopy.

Observations were made of cryo-preserved honey bee tracheal mites Acarapis woodi (Rennie) using scanning electron microscopy. We describe various new morphological attributes of A. woodi based on the ability of the cryo-technique to capture live mites in natural positions and observe the Low-Temperature Scanning Electron Microscopy (LT-SEM) photographs under a 3-D viewer. Most striking was the observation that each leg has the ability to independently twist its segments with the ambulacrum rotating a minimum of 180 degrees during locomotion; this is a more sophisticated form of locomotion than has been proposed for the Acari. Adult daughter mites are known to be the dispersal instar moving from the tracheal tube to the thoracic hairs of the bee and then transferring to a new bee. We hypothesize that adult tarsal claws and setae on the legs play a role in attachment to hairs during dispersal. However, our evidence is that none of the life stases use their tarsal claws within the tracheal tubes. Larvae were observed to be 'freely moving' within the tracheal system, their tarsal claws rendered inoperative due to an enlarged swollen pulvillar pad. The solenidia of leg I are now known to have striations and the famulus is bifurcated. The bifurcated famulus, solenidial striations, and segmentation of leg IV of females may have taxonomic implications in the family Tarsonemidae. The body and leg setae of adults appear to be used as a tactile tool to sense the amount of space within the tracheal tubes; most of the setae are oriented distally and may help the mite to measure the space or radius of the tracheal tubes. The modified caudal region of the male revealed remnants of the h1 and h2 setae and a smooth clean surface, void of a film, supporting that pharate nymphs are not attached in this species.