Design of insect unguitractor apparatus.

The structure of the unguitractor system of insect legs was studied using scanning and transmission electron microscopy. On the base of serial semithin sections, the 3-D reconstruction of structures of the terminal tarsomere was obtained and the arrangement of different types of cuticle was demonstrated. The membrane connects all structures of the system and divides the terminal parts of the claw flexor muscle into the external (unguitractor plate) (UT) and inner (tendon) ones. Elastic nonlayered cuticle located between the claws and the posterior wall of the terminal tarsomere is interpreted as a claw-returning string. Cuticle surrounding the apodeme of the posterior wall of the terminal tarsomere contains large porous canals. The anterior part of the terminal tarsomere has an invagination that forms a plate facing toward the UT. This plate comprises the UT anteriorly and laterally and contains a microtrichia field (MF) on its distal part. The surface of the UT has a complex microstructure providing fixation to the MF of the corresponding surface of the anterior wall of the terminal tarsomere. Microtrichia of the UT and MF are directed to opposite directions and provide anchorage of the UT whenever the flexor claw muscle contracts. The microsculpture of UT and MF for representatives of Odonata, Coleoptera, Hemiptera, Hymenoptera, and Diptera was compared. It is suggested that small insects, which are able to walk quickly on thin rods, usually have wide microplates on the UT plate to provide quicker fixation-release of the UT in the contact area. Insects using the legs to produce hollows in the soil usually have a large UT with well-developed microtrichia on its surface to produce strong friction forces in the contact area for a long period of time. © 1996 Wiley-Liss, Inc.