FRICTIONAL SURFACES OF THE ELYTRA-TO-BODY ARRESTING MECHANISM IN TENEBRIONID BEETLES (COLEOPTERA, TENEBRIONIDAE) - DESIGN OF CO-OPTED FIELDS OF MICROTRICHIA AND CUTICLE ULTRASTRUCTURE

In beetles, the system responsible for an attachment of forewings (ely tra) to the thorax consists of interlocking fields of microtrichia (MT ) located between thorax and body and between left and right elytra. T he present study provides comparative data about microtrichia design o n the thorax and elytra in three species of tenebrionid beetles (Tribo lium castaneum, Tenebrio molitor, Zophobas rugipes) (Coleoptera: Teneb rionidae), which are different in their size. The length, width, densi ty and directionality of microtrichia in 13 MT fields (4 on the thorax , 1 on the abdomen, 7 on the elytra, and 1 on the costal Vein of the h indwing) were quantified. (1) Parameters studied are dependent on the dimension of an insect. The length of the microtrichia of most fields compared increases with an increase in body size. The MT width in the majority of fields increases with an increase in the elytra length. Th e MT density decreases with an increase in the elytra length. (2) Both width and length of microtrichia increase with an increase in the dis tance between single MT. The density of outgrowths increases with an i ncrease in their length and width. (3) The fields oriented along the s ame spatial axis constitute functional groups responsible for a partic ular direction. Go-opted fields can be oriented in the same or opposit e directions. (4) The design of MT correlates in co-opted surfaces. Th ere are 3 field groups, which were stated as functionally correspondin g to one another: the medial, anterio-lateral, and posterio-lateral. T he lengths and widths of microtrichia from fields of these functional groups were quite similar in corresponding fields. Length-to-width rat ios of MT in elytral fields were usually weakly correlated with those of thoracic fields. The distances between microtrichia on the elytra s urface directly depended on those of the thorax. Distance-to-width rat io of MT of one surface slightly increased with an increase in this pa rameter on the co-opted surface. The MT densities on co-opted fields w ere usually quite different. (5) The ultrastructure of the cuticle sug gests differences in the material properties of the cuticle between MT fields. The thoracic fields usually consist of elastic cuticle, where as elytral fields are much harder. Usually, a MT held of elastic cutic le corresponds to the held composed of hard cuticles. The study also p rovides information about the ultrastructure of epidermal cells and ab out the design of pore channels, which are presumably responsible for production and transport of an adhesive secretion into the area of con tact between lateral fields. Sensory organs monitoring contact between co-opted binding sites were also studied. The results of this study m ay aid in understanding the morphological basis of cuticular microscul ptures acting as frictional devices. (C) 1998 Elsevier Science Ltd. Al l rights reserved.