Ultrastructure of the thoracic dorso-medial field (TDM) in the elytra-to-body arresting mechanism in Tenebrionid Beetles (Coleoptera: Tenebrionidae).

Beetles with flying ability lock their elytra (forewings) to the thorax or/and abdomen using complex locking devices. These structures are often supplemented with microtrichia fields of the inner surface of the elytra and adjacent parts of the pterothorax. The present study provides information about the ultrastructure of microtrichia of the dorso-medial fields of the thorax (TDM) in tenebrionid beetles (Tribolium castaneum, Zophobas rugipes). Epidermal cells located under the TDM field contain large electron-lucent vesicles connected to rough endoplasmic reticulum. Microtrichia and underlying cuticle of the TDM have a high density of pore channels, which are responsible for transport of an epidermal secretion onto the TDM surface. In order to show the presence of the secretion on the cuticle surface, TDM fields of air-dried specimens were compared with those in specimens after two treatments, such as (1) dehydration in ethanol and acetone, and (2) dental-wax-cast technique applied to living beetles. This revealed the presence of the nonvolatile film on the intact microtrichial surface. Possible functions of this film are suggested to be (1) the increase of adhesive forces in the contact area and (2) providing soft coupling and release of two corresponding parts of the elytra-locking device. J. Morphol. 240:101-113, 1999. © 1999 Wiley-Liss, Inc.