Abstract:

Objective   To observe the ultra-structure of the legs and external genitalia of Demodex folliculorum(D.f.) and Demodex brevis(D.b.) using environmental scanning electron microscopy（ESEM）， and to study the value of the difference of these structures for systematics. Methods  Samples of the two species of mites were collected by special scrapers and pliers from the foreheads of adults. After being cleaned and picked up with the micro-manipulative technique within one hour， the living mites were observed and photographed under ESEM. Results  Ultra-structures of the legs and external genitalia of Human Demodex were clearly observed under ESEM. There were differences between the two species not only in the shape and number of the tarsal claws, but also in the position and shape of the external genitalia. Legs of D.f. were sturdier than those of D.b., composed of one bifid claw and one trifid claw, which were blunt on each dactylus, and claw spurs and femoral spurs could obviously be found; the external genitalia of male D.f. lay dorsally in the central position of four dorsal podosomal setae, and the penis looked like a head of Chinese writing brush which could stretch out from and draw back to a longitudinal genital orifice; the longitudinal vulva of D.f. was located ventrally in an intermediate position between the fourth pair of legs, and the vulva together with a curved ruga in front of it looked like an anchor. Legs of D.b. were slender, and claws on dactylus were spiculate and different in number and shape, but no claw spur and no femoral spur were found; the longitudinal vulva of D.b. was ventrally behind the level of the 4th pair of legs，and the vulva plus the curved folds in the front and back looked like a “工". Fifty D.b. were observed but no penis was found. Conclusion  Without any special pretreatment, the ultrastructures of samples of human Demodex are lifelike under ESEM. Differences between D.f. and D.b. in the ultra-structures of the legs and external genitalia could be important for the systematics of human Demodex.

Key words: Genitalia； Ultrastructure； Environmental scanning electron microscopy