Wolfgang Rössler

Functional morphology and development of tibial organs in the legs I, II and III of the bushcricketEphippiger ephippiger (Insecta, Ensifera)

SummaryThe anatomy of the complex tibial organs in the pro-, meso- and metathoracic legs of adults and larvae of the bushcricketEphippiger ephippiger is described comparatively. The subgenual organ and the intermediate organ are differentiated in the same way in legs I, II and III; the anatomy of the crista acustica and the tracheal morphology are significantly different. The final number of scolopidia in the tibial organ of each leg is present at the time of hatching. In the subgenual organ, the number of scolopidia is the same in all legs; in the intermediate organ, and especially in the crista acustica, the number of scolopidia decreases from leg I to legs II and III. In the first larval instar, the morphology of the tibia, the course of the trachea and the anatomy of accessory structures are developed in the same way in each leg. The specific differentiations forming the auditory receptor organ in leg I, such as the acoustic trachea, the tympana and tympanal cavities, develop step by step in subsequent instars. The auditory threshold recorded from the tympanal nerve in the prothoracic leg of adults is remarkably lower than in the meso- and metathoracic legs. Morphometrical analyses of structures that are suggested to play a role in stimulus transduction on scolopidia of the crista acustica reveal significant differences in the three legs.

Postembryonic development of the complex tibial organ in the foreleg of the bushcricket Ephippiger ephippiger (Orthoptera, Tettigoniidae)

SummaryThe postembryonic development of the morphology and anatomy of the complex tibial organ in the foreleg of the bushcricket Ephippiger ephippiger is described. All the receptor cells are present in the subgenual organ, the intermediate organ and the crista acustica in the 1st larval instar. Generally, even in the 1st instar, the arrangement of the scolopidia in the three organs resembles the adult structure. The acoustic trachea, the tympana, the tympanal covers and the acoustic spiracle develop step by step in subsequent instars. The acoustic trachea resembles the adult structure for the first time in the 4th instar, although its volume is still small. The auditory threshold curves recorded from the tympanal nerve in instars 4, 5 and 6 show the same frequency maxima as those in the adult. The overall sensitivity significantly increases after the final moult. The dimensions of structures that lie within the crista acustica and that are probably involved in stimulus transduction and in frequency tuning have been analysed. The dorsal wall of the anterior trachea, the tectorial membrane and the cap cells have similar dimensions, especially in the last three instars and in adults.

Structure of atympanate tibial organs in legs of the cave-living ensifera, Troglophilus neglectus (Gryllacridoidea, Raphidophoridae)

Troglophilus neglectus (Gryllacridoidea, Raphidophoridae) is a nocturnal Ensifera which can be found in caves of Slovenia. The anatomy of the tibial organs in the fore‐, mid‐, and hindlegs, as well as the external morphology of the proximal fore‐tibia and the prothoracic tracheal system, is described comparatively. In the prothorax and in the forelegs, no sound‐conducting structures such as an acoustic trachea, enlarged spiracles, or tympana are developed. A group of 8–10 campaniform sensillae is located in the dorsal cuticle of the proximal tibia. In each leg, the tibial organ complex is built up by two scolopale organs, the subgenual organ and the intermediate organ; the structure and the number of scolopidia is similar in each leg. No structure resembling the crista acoustica is found. The subgenual organ contains around 30 scolopidia; the intermediate organ is subdivided into a proximal part containing 8‐9 scolopidia and a distal part with 5–6 scolopidia. The two groups of scolopidia are not directly connected to the tracheal system. The tibial organs in the forelegs are insensitive to airborne sound, and they appear to be more primitive compared to those found in members of the Tettigoniidae and the Gwllidae. The results indicate that the complex tibial organs in all legs of T. neglectus are primarily vibrosensitive.

Functional morphology of bushcricket ears: comparison between two species belonging to the Phaneropterinae and Decticinae (Insecta, Ensifera)

SummaryThe morphology of the complex tibial organs in the forelegs of two bushcricket species belonging to the Phaneropterinae and Decticinae (Tettigoniidae) is described comparatively. In both species the tibial organs are made up of the subgenual organ, the intermediate organ and the crista acustica; the latter are parts of the tympanal organs and serve as auditory receptors. The very thin tympana in the forelegs ofPholidoptera griseoaptera (Decticinae) are protected by tympanal covers whereas inLeptophyes punctatissima (Phaneropterinae) the tympana are thicker and fully exposed. The overall auditory sensitivity ofL. punctatissima is lower and the sensitivity maximum of the hearing threshold lies at higher frequencies compared toP. griseoaptera. The number of scolopidia in the three scolopale organs and the dimensions of parts of the sound conducting system differs in the two species. In the crista acustica ofL. punctatissima a higher number of scolopidia is distributed in a smaller range than inP. griseoaptera; the scolopidia are especially concentrated in the distal part. Morphometrical analyses indicate that the dimensions of the spiracles, the acoustic trachea and the tympana determine the overall auditory sensitivity and that the arrangement of the scolopidia and the dimensions of structures in the crista acustica affect the frequency tuning of the hearing threshold.

Complex tibial organs in fore-, mid-, and hindlegs of the bushcricket Gampsocleis gratiosa (Tettigoniidae): comparison of morphology of the organs

The structure of the complex tibial organs in the fore‐, mid‐, and hindlegs of the East Asian bushcricket Gampsocleis gratiosa (Tettigoniidae, Decticinae) is described comparatively. In each leg the tibial organs consist of three scolopale organs: the subgenual organ, the intermediate organ, and the crista acoustica. Only in the forelegs are the tibial organs differentiated as tympanal organs, and sound transmitting structures (acoustic trachea, tympana, and tympanal covers) are present. The morphology of the tracheae in the mid‐ and hindlegs is significantly different from that found in the forelegs. The number of scolopidia in the subgenual organ is highest in the midleg and lowest in the foreleg; in the intermediate organ the number is also highest in the midleg, and the fore‐ and hindleg contain 40% fewer scolopidia. In the crista acoustica, the number of scolopidia decreases from, the fore‐ to the mid‐ and hindlegs. The morphology and the dimensions of the scolopidia and the attachment structures within the crista acoustica of the mid‐ and hindlegs differ strongly from those in the foreleg. The results indicate that, in addition to the presence of a sound transmitting system, the specific differentiations within the crista acoustica are important for the high auditory sensitivity of the tibial organs in the forelegs.

Omega AGA toxin IVA blocks high-voltage-activated calcium channel currents in cultured pars intercerebralis neurosecretory cells of adult locusta migratoria

Using the whole cell patch-clamp technique, calcium (Ca) channel currents from cultured medial neurosecretory cells (MNSCs) of Locusta migratoria (Rössler and Bickmeyer, 1993) were investigated. The calcium channel blocker omega AGA toxin IVA (AGA IVA) blocks a fraction of these calcium channel currents in approximately 30% of MNSCs, without a shift in the I-V relationship. The block can be at least partially reversed by strong depolarizing voltage pulses as described for vertebrate neurones from Mintz et al. (1992). The existence of probably more than three calcium channel types in insects is discussed.

Morphology of the tibial organs of acrididae: Comparison of subgenual and distal organs in fore-, mid-, and hindlegs of Schistocerca gregaria (Acrididae, Catantopinae) and Locusta migratoria (Acrididae, Oedipodinae)

The structure of the complex tibial organs in the fore‐, mid‐, and hindlegs of two grasshopper species, Schistocerca gregaria (Acrididae, Catantopinae) and Locusta migratoria (Acrididae, Oedipodinae), is described. In each leg the tibial organs consist of two scolopale organs: the subgenual organ and the distal organ. Both organs are located in the hemolymph channel. The subgenual organ has a sail‐like structure, and its scolopidia are oriented perpendicular to the long axis of the leg. The number of scolopidia in the subgenual organs is lower in Locusta migratoria than in Schistocerca gregaria. The scolopidia of the distal organ are clearly spearated from those of the subgenual organ and lie parallel with the long axis of the legs. They insert distally on an attachment plate that lies in the hemolymph channel. The subgenual organs and the distal organs are smaller in the hindlegs than in the fore‐ and midlegs, and this difference is especially pronounced in Locusta migratoria. The complex tibial organ of Locusta and Schistocerca is very similar in structure and cellular composition with that of Periplaneta (Blattidae). In tettigoniids and gryllids the distal organ is differentiated into an intermediate organ and the crista acoustica.

Comparative Investigation on the Morphology and Physiology of the Auditory Receptor Organs of Seven Species of Bushcrickets

Seven species of bushcrickets were investigated morphologically and physiologically in order to find out adaptations of the receiver system to the parameters of the conspecific song. The following species were used: Decticus verrucivorus (D.v.), Decticus albifrons (D.a.) and Psorodonotus illyricus (P.i.); Tettigonia cantans (T.c.) and Tettigonia viridissima (T.v); Ephippiger ephippiger (E.e.), Mygalopsis marki (M.m.). Despite of partly great differences in the time-amplitude patterns and the frequency content of the different stridulatory songs, the hearing organs of the forelegs of the seven species have in some respects very similar properties. For instance, the audible range is nearly the same for all the seven species although there are differences in the morphology and the number of receptor cells between the tympanal organs of the different species. The audible range of all the seven species lies between 2 to 70 kHz which could be revealed by single cell recordings of all the auditory receptor cells (Kalmring et al. 1990).

Similar structural dimensions in bushcricket auditory organs in spite of different foreleg size: Consequences for auditory tuning

The bushcricket species Decticus albifrons, Decticus verrucivorus and Pholidoptera griseoaptera (Tettigoniidae) belong to the same subfamily (Decticinae) but differ significantly in body size. In spite of the great differences in the dimensions of the forelegs, where the auditory organs are located, the most sensitive range of the hearing threshold lies between 6 and 25 kHz in each case. Only in the frequency range from 2 to 5 kHz and above 25 kHz, significant differences are present. The anatomy of the auditory receptor organs was compared quantitatively, using the techniques of semi-thin sectioning and computer-guided morphometry. The overall number of scolopidia and the length of the crista acustica differs in the three species, but the relative distribution of scolopidia along the crista acustica is very similar. Additionally, the scolopidia and their attachment structures (tectorial membrane, dorsal tracheal wall, cap cells) are of equal size at equivalent relative positions along the crista acustica. The results indicate that the constant relations and dimensions of corresponding structures within the cristae acusticae of the three species are responsible for the similarities in the tuning of the auditory thresholds.