J. exp. Biol. 129, 25-40 (1987) 2 5Printed in Great Britain © The Company of Biologists Limited 1987

EFFECTS OF WING CAMPANIFORM SENSILLA LESIONSON STRIDULATION IN CRICKETS

BY KARL-HEINZ SCHAFFNER* AND UWE T. KOCHf

Max-Planck-Institut fur Verhaltensphysiologie, Abteilung Huber,D-8131 Seewiesen, Federal Republic of Germany

Accepted 12 December 1986

SUMMARY

The degradations in the cricket's calling song after lesions of the cubitalcampaniform sensilla (CCS) are investigated using extracellular recording andangular movement recording techniques. In the intact male, nerve potentials fromthe CCS during the closing stroke are demonstrated. In the lesioned male, syllableshortenings and missing syllables can be traced to abnormalities in the wing motion:irregular stops ('sticking'), anomalously high closing speeds with sound emission('overspeed'), or high closing speeds without sound emission ('slipping') areobserved. Despite these defects, the activation pattern of the main opener and closermuscles remains completely unaffected. The defects are interpreted as disturbanceof a regulatory system normally maintaining proper engaging forces of the wings.

INTRODUCTION

Schaffner & Koch (1987) showed that lesions of the cubital campaniform sensilla(CCS) cause severe alterations in the song of the male cricket, and that these 'lesionsongs' are less attractive to the female. However, we did not consider which partsof the sound-generating system fail when the lesion songs occur. One possibleexplanation for missing syllables could be a lack of wing motion due to missingactivity in the wing muscles. Another possibility could be that the wings slide pasteach other without touching and thus generate no sound, or that the wings 'get stuck'at the beginning of the motion. An investigation of these possibilities will help toexplain why the CCS play such an important role in cricket sound production.

In this paper the function of the CCS is investigated further. To this end, a varietyof experimental techniques was used: extracellular recordings from the cubital nerve,recordings of the wing motion and myograms of the large opener and closer muscles.The wing motion recordings were used to analyse the sliding or sticking

•Present address: Abteilung Vergleichende Neurobiologie, Universitat Ulm, Postfach 4066,D-7900 Ulm, FRG.

f Present address: Fachbereich Biologie, Universitat Kaiserslautern, D-6750 Kaiserslautern,FRG.

Key words: motion defects, movement control, sensory feedback, extracellular recording.

26 K. -H. SCHAFFNER AND U. T . KOCH

motion, while the myograms were used to check if any abnormalities in the motoroutput pattern could be the cause of the observed disturbances.

MATERIALS AND METHODS

Extracellular recordings from the cubital nerve

Male Gryllus campestris were first selected as 'good singers' (Schaffner & Koch,1987). The animal was tethered carefully using Plastilin. The wire used for theextracellular recordings was copper or steel wire (20 or 30 jxm in diameter), insulatedwith varnish except at the tip.

Two recording sites were used. In a unipolar electrode arrangement, the activeelectrode was inserted into a small hole that had been pierced in the cubital vein nearthe CCS. The indifferent electrode was placed in the mesothorax or, in laterexperiments, between the fourth and fifth abdominal segments. In the differentialelectrode arrangement, two electrode wires were placed medial and lateral to thecubital vein. With this technique, lesions of the cubital nerve were avoided. Inaddition the cross-talk from the large wing muscles was substantially reduced.

The recording wires were usually fixed with 'insect wax' made from 66 % beeswaxand 34 % colophonium. The wires were also fixed on the anal field in order to reducethe load on the insertion site. Finally, the wires were waxed to the pronotum and ledto the preamplifiers. The wing motion was not hampered by the electrodes. Theextracellular potentials, as well as the sound signal of the calling songs were stored onan instrumentation tape recorder (Racal Store 7DS). The data were later played backon a storage oscilloscope, or, at reduced speed, on a chart recorder (SchwarzerUS266). Fifteen males were used for these recordings. The wing nerve recordingswere made in collaboration with Dr G. Kamper, whose help and advice is gratefullyacknowledged.

Recordings of wing movements during stridulation

For precise wing motion recordings, the method of inductive angular measure-ments with miniature sensing coils was used (Koch, 1980). We also used the specialtechnique of position stabilization and signal analysis by analogue computing asdescribed in Koch & Elliott (1983) and Elliott & Koch (1983). This improved systemof movement recording permits the direct display of the movement of the wingsrelative to each other and also the measurement of relative wing velocity. Theposition-sensing coils were lx2xO-2mm and consisted of 30 windings of copperwire (17^m in diameter). Mechanograms of 12 male Gryllus campestris were madebefore and after lesions of the cubital nerve.

Electromyogram recordings during stridulation

The males were carefully tethered with Plastilin leaving the pleural area of themesothorax free. The electrodes were placed in M99 (remotor coxae) and M90

Cricket stridulation 27

(subalar) following the method of Kutsch (1969). For each muscle, two electrodewires (steel, 30 ̂ m in diameter) were inserted into the upper third of the epimerum,and fixed with insect wax. The indifferent electrode was inserted into the abdomenbetween the fourth and fifth segments. Electromyogram (EMG) potentials andacoustic signals were amplified and stored on a tape recorder (Racal Store 7DS) andlater played back at reduced speed on a chart recorder (Gould). For analysis of thetiming, EMG potentials were analysed with a peak-detecting window discriminator,whereas the onset of the sound was measured using a level discriminator applied tothe envelope signal. For selected 1-min sections of the recordings, these timingsignals were stored on the RK05 disk of the PDP 11/40 computer using the digitalinputs of the LPS11 laboratory interface (Schaffner & Koch, 1987).

The crickets were kept in glass jars (8 cm in diameter, with a peat substrate) for theEMG and sound recordings. As described by Huber (1965), the males are notdisturbed in their singing behaviour by the chronically implanted electrodes. Eventhe circadian rhythmicity of singing is maintained (see Wiedenmann & Loher, 1984).EMG recordings of four G. bimaculatus males with lesions of the cubital nerve onboth sides were made.

RESULTS

Electrical activity associated with the cubital nerve

In a large proportion of the recordings, especially when the indifferent electrodewas placed in the thorax or abdomen, strong cross-talk from the main wing muscleswas observed (see Fig. 2B). However, muscle potentials have considerably slowerrise and fall times, and thus it was possible clearly to distinguish the fast nervepotentials. In addition, the muscle potentials helped in gaining precise time relation-ships between the nerve signals and the wing motion, together with the sound signal.With the electrodes inserted directly into the cubital vein, we observed the changes inthe sound pattern described by Schaffner & Koch (1987). With electrodes inserteddirectly into both cubital veins, chirps with missing syllables were observed. Thuswe assume that in these recordings the wire had damaged or destroyed the cubitalnerve and/or the CCS.

In differential recordings, extracellular nerve potentials (durations less than 1 ms)were observed during sound production (Figs 1, 2). In five animals, bursts of up to20 nerve impulses were registered, mostly correlated with the closing phase and alsomostly correlated with a somewhat deformed syllable envelope (Fig. 1). As seen inFig. 2A, we also recorded single nerve impulses during the second half of the closingstroke. These were sometimes followed by a series of smaller impulses, which can beinterpreted as a series of repetitive discharges. Thus, it is possible to record sensoryunits from the region of the cubital nerve during singing, but further studies mustshow the precise origin and time relationship of such potentials. To explain theseresults, we assume that the units recorded here react only to strong force peaks.

28 K.-H. SCHAFFNER AND U. T . KOCH

These may occur if the movement of the wings is somewhat irregular, i.e. a suddensticking of the wing could produce sharp transient force peaks (see also Discussion).

Motion pattern of intact song

Fig. 3A shows wing position and velocity, and sound envelope of a four-syllablechirp in an intact G. campestris male. This typical recording was taken from a longcontinuous song bout. The four repeated movements can be easily distinguished.Between chirps, a characteristic resting position (about two-thirds open) is assumed.The first syllable is started with a further opening motion from this resting position.The wings remain in this maximal open position for about 5-10 ms. Then the firstclosing of the wings produces the sound of the first syllable. Four opening andclosing phases can be seen. Sound is always and only produced during the closingphase. The closing speed is only about one-third of the opening speed. The timecourse and peak speed of the opening phase vary between syllables. In contrast tothis, the time course of the closing phase is remarkably constant. At the beginning of

—*—«• *|l ^—

Fig. 1. Extracellularly recorded activity from the cubital nerve correlated to sound pulsesin an otherwise intact male Gryllus campestris. The position of the electrodes on the rightwing is indicated by the asterisks in the inset. Note that groups of impulses are related tothe somewhat disturbed syllable envelopes (arrows).

Cricket stridulation 29

1 j

20 ms

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Fig. 2. Cubital nerve potentials (upper traces) and corresponding syllable envelopes(lower traces) during differential recording with the electrodes placed as shown in theinset of Fig. 1 (A), and with unipolar recording where the indifferent electrode wasplaced in the abdomen (B). Recordings are from the right wing of Gryllus campestris. InB groups of muscle potentials (cross-talk) are seen corresponding to opening and closingphases. The arrows indicate nerve potentials with much faster (>1 ms) rise and fall timestowards the end of the closing phase.

the closing phase, wing speed rises in a ramp-like fashion, and later remains at analmost constant value, which we will call the 'closing speed base value'. While themaximum opening position of the wings is the same for each syllable, the endpoint ofthe closing motion proceeds further inwards for each subsequent syllable in thechirp. This means that, starting on the same point of the file, more and more lateralteeth are used in the later syllables of the chirp. After each closing, the wings areopened again to the same maximum opening position. Thus, the systematic increasein syllable duration is caused by the wings moving further inwards in each syllable.At the end of the fourth syllable, the wings are closed furthest. Then they are moved

30 K.-H. SCHAFFNER AND U. T . KOCH

back to the interchirp resting position. To obtain a good data base of referencerecordings, wing motion and sound envelope were recorded from all experimentalanimals in the intact state. They showed a very close correspondence in the featuresdescribed above.

Motion pattern of lesion songs

After lesions of the cubital nerve proximal to the CCS, the wing movementrecordings were resumed. Examples taken from stable calling songs are presented inFig. 3B—F (same animal as Fig. 3A). In Fig. 3B, the wings do not close (arrow) afterthe opening for the second syllable. Accordingly, no sound is produced before thethird syllable, when the wing is opened somewhat further than the normal openingposition. Fig. 3C shows a motion stop after the second syllable. After the failure ofthe third syllable, there is a further opening starting at the (successful) fourth

Open A B

Close

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Close

L _JLL_IJLFig. 3. Recordings of wing movement in male Gryllus campestris with a set-up asdescribed by Elliott & Koch, 1983. Top trace, distance between right and left wing tips;middle trace, relative wing speed; bottom trace, sound envelope. White arrows indicateopening direction, black arrows closing direction. Small black arrows indicate stopsduring closing, and asterisks indicate abnormally high closing speeds. (A) Chirp of anintact male; (B-F) chirps selected from recordings of the same male after lesion of bothcubital nerves proximal to the cubital campaniform sensilla.

Cricket stridulation 31

syllable. The base value of the closing speed (about 0-7° ms"1; Koch, 1980) is onlykept for a short time. After this, the closing speed becomes very fast and rises to threetimes the opening speed. At the same time, syllable duration is markedly reduced. Inthese cases the sound envelope often has sharp peaks and other deformations.

Examples of other missing syllables are shown in Fig. 3D—F. In Fig. 3F, all foursyllables are missing. The inward movement always stops at the same position,which is approximately the interchirp resting position. Although very many combi-nations of missing and deformed syllables have been found, deformation and/or lossof the third and fourth syllable seem to occur more often.

Further examples of the variability in the movement patterns are shown in Fig. 4.The upper part shows the intact song, the lower part the songs after the lesions. Onecan clearly distinguish the alteration in the lesion song. Sometimes, sound is evenproduced during the opening phase (Fig. 4A). In lesion songs, the closing speed base

Fig. 4. Wing movement recordings from three different Gryllus campestris (A,B,C).Trace identification as in Fig. 3. Upper set of traces, intact animals; lower set of traces,the same males after lesions of cubital campaniform sensilla on both wings. Small blackarrows indicate stops of movement. Asterisk indicates sound emission during the openingstroke.

32 K.-H. SCHAFFNER AND U. T . KOCH

value is often not maintained. Whenever higher closing speeds occur together witheffective sound emission, the closing speed can be assigned to a multiple of the basalvalue (Fig. 5A,B). Several of these multiples can occur in a single syllable; the speedrecord then shows 'steps' (e.g. Fig. 5A, last syllable; Fig. 5B, penultimate syllable).As mentioned above, these increased speeds result in a strongly reduced syllableduration (sometimes less than 5 ms).

The movement recording results can be summarized as follows.(1) The plectrum slides over the file without sound production at a high speed

('slipping'). The slipping speed may be as high as three times the opening speed.Slipping can occur during the whole closing phase, which leads to a missing syllable(Fig. 5C). If slipping occurs during a part of the syllable (often near the end of theclosing phase), syllable duration is reduced accordingly.

(2) The plectrum stops its motion: it 'gets stuck' on the file. Sticking can occurin any part of the closing phase and may persist for very short times or for the wholesyllable cycle. Some sticking may also occur at the beginning of intact syllables, but itis always followed by 'normal' sound and normal speed. Often, there is a small soundemission (one-quarter of normal intensity) at the beginning of a syllable just beforesticking takes place (e.g. Fig. 3E,F).

(3) Anomalously high closing speed with sound emission ('overspeed'). Thisoften occurs after some initial sticking and leads to syllable shortening (e.g.Fig. 3B,C).

(4) In intact males, one never observes sound production during the openingphase. Even in lesioned males it occurs rarely, except where the male changespermanently to a left-over-right singing position (Elliott & Koch, 1983; Schaffner,1985).

(5) The interchirp resting position and the maximum opening position show astronger variance in lesioned songs.

O p e n A B C

Close

Fig. 5. Wing movement recordings from three animals with lesions of the cubitalcampaniform sensilla (Gryllus campestris). Trace identification as in Fig. 3. In A and B,the wing closing speed reaches multiples of the basal closing speed value (indicated bydashes) with sound emission but reduced syllable duration. In C, extremely high closingspeeds are seen (slipping) with almost no sound emission.

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34 K.-H. SCHAFFNER AND U. T. KOCH

These findings also explain why syllable shortening was found in one-sided lesionexperiments, whereas missing syllables were only prominent in two-sided lesions.

Muscular activity during stridulation

A plausible explanation for the movement anomalies could be changes in thecentrally programmed neuromotor activation pattern of the main opener and closermuscles (described by Huber, 1965; Ewing & Hoyle, 1965; Kutsch, 1969; Innen-moser, 1974; Weber, 1974; Elepfandt, 1980). We therefore made EMG recordingsof the M99 (opener) and M90 (closer) muscles in males with lesions of the cubitalnerve proximal to the CCS.

The potentials of the opener and closer muscles (M99 and M90) are unaffected bythe lesions of the cubital nerve (Fig. 6). The time pattern of the EMG potentialscorresponds very closely to the patterns reported for the intact male. The closermuscle M90 is activated 5-7 ms before the appearance of the sound. This delay iscaused by the time necessary to activate the muscles and the wing mechanics. As inthe intact male, several motor units may be activated, especially near the end of thechirp. The opener muscle M99 is activated in alternation with M90, marked byarrows in Fig. 6A. As a result of cross-talk, the trace of the opener muscle alsocontains the closer muscle signal.

The muscle potentials show a striking stability, even where the sound intensityenvelope indicates missing or mutilated syllables. This is illustrated in Fig. 6B—D,F(asterisks). Although the M90 trace shows an undisturbed four-syllable pattern, thesound envelope signal in Fig. 6B shows only three syllables: the second syllable ismissing. Fig. 6C shows a strong deviation from the usual 30 Hz syllable pattern. Thesound is generated between the second and third syllables, and the third syllable ismissing, although M90 had been activated correctly. Presumably, the wings gotstuck at the beginning of the second syllable and only closed when the peak ofmuscular power was reached, just before the opening stroke for the third syllable.Such events were recorded in 3-4 % of the chirps and must be especially unattractiveto the female (see Thorson, Weber & Huber, 1982; Schaffner & Koch, 1986). Inaddition, it can be shown that the three-syllable chirps occurring in lesion songs evenwithin long continuous singing bouts are in fact four-syllable chirps with a missingfirst or last syllable (e.g. Fig. 6F).

In order to give a more quantitative evaluation of these findings, we usedjoint—interval (J-I) histograms of the EMG and the sound envelope signals of thesame 1-min sections of stable calling song. The J—I histogram of the closer musclesignal (Fig. 7A) shows remarkable stability. The data points scatter by only ±6ms.

Fig. 7. Comparison of joint-interval histograms of a Gryllus bimaculatus male withlesions to the cubital campaniform sensilla. The same section of recording was analysedfor electromyogram (EMG) (M90) signals and for sound signals. (A) Histogram of theEMG signals; (B) histogram of the sound envelope onset (25% level). Intervaldefinitions are illustrated by the inset in A. Filled arrows, syllables missing; open arrows,syllable displacement. Note that although the sound signal shows missing and displacedsyllables, no corresponding deviations from the undisturbed pattern are observed in theEMG signal.

Cricket stridulation 35

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36 K. -H. SCHAFFNER AND U. T . KOCH

This is in good agreement with the data found in intact G. campestris (Weber, 1974).In the J-I histogram of the sound envelope signal, however, a much larger scattercan be seen, corresponding to substantial disturbances in the acoustic output of thelesion song. Although some increase in the scatter can be assigned to the normalirregularities in the onset of sound, a number of data points (filled arrows) located attwice the standard interval indicate the occurrence of missing syllables (7 out of 600data points). A further set of data points (open arrows) is closer to the average yetclearly distinguishable from the main 'cloud'. These points represent strong syllabledisplacements (see Fig. 6C) or syllable shortenings.

The irregularities found in the sound output and in the movement recordings inmales with lesions of the CCS cannot be found, therefore, at the level of musclepotentials in the main stridulatory muscles. The centrally generated pattern persistsas if the male were intact. It is not changed during even the most severe disturbancesof the sound output.

DISCUSSION

In wing movement recordings from males with lesioned cubital nerves, oneprominent feature is the enhanced closing speed, which is often associated with nosound production. In examples where sound is produced at high closing speeds, thespeed values are always multiples of the basal closing speed. These findings accordwith the 'clockwork' hypothesis (Elliott & Koch, 1985; U. T. Koch, C. J. H. Elliott,K.-H. Schaffner & H.-U. Kleindienst, in preparation), which proposes that theresonance properties of the harp control the closing speed of the wings. In the intactmale, the plectrum jumps from one file tooth to the next, and this takes the time ofone sound cycle. If the plectrum jumps over n teeth per sound cycle - that means theanimal uses every wth tooth — the closing speed must be n times the base value.Intermediate speeds, such as 1-5 times the base value, should not occur, as indeedthey do not (see Fig. 5). Syllables with closing velocities of twice the base velocitywere also observed in males with a reduced syllable duration (see Elliott & Koch,1983). In contrast, when the wings close without sound production (slipping), theharp is not engaged in speed control. Accordingly, a continuous spectrum of closingspeeds up to very high values is observed (Figs 3B—E, 5C) (see U. T. Koch, C. J. H.Elliott, K.-H. Schaffner & H.-U. Kleindienst, in preparation).

EMG recordings present the surprising result that the neuromuscular patterngenerates perfect opening and closing strokes while severe defects are seen in thesound signal. This must mean that the central pattern generator for singing,presumed to be located in the thoracic ganglia (Bentley, 1969; Kutsch & Otto, 1972),is not affected in its basic rhythmicity by the removal of influence from the CCS.These statements are based on recordings from the two most important opener andcloser muscles, but they do not exclude a CCS influence on some of the lessprominent muscles (see Schaffner, 1985).

For the hypotheses formulated below we should bear in mind the following.

Cricket stridulation 37

(i) Male crickets have special campaniform sensilla, which are located andoriented on the wing in such a way that they are able to measure thrust forces alongthe file. The extracellular recordings from the cubital nerve show song-correlatednerve potentials mostly when the file is at maximum thrust load near the end of thesyllable.

(ii) Lesions of the cubital nerve that remove the influence of the CCS cause ahigh frequency of missing syllables, significantly reduce syllable intervals andincrease their variance, and lead, in part, to drastic reductions in syllable duration.Songs modified in this way have a significantly reduced attractiveness in femalephonotaxis (Schaffner & Koch, 1987).

(iii) The alterations in the lesion songs can be traced back to changes inthe wing movement, to an increased wing closing speed with sound production(overspeed) resulting in shorter syllables, to wing closing without sound production(slipping) causing syllables to be missed or markedly shortened, and to stops inwing motion (sticking) causing missing or shortened syllables. These alterationscan affect only parts of a syllable, and/or several of them can affect the samesyllable.

(iv) In spite of these well-documented changes in the wing movement, themotoneuronal excitation pattern to the major wing opening and closing muscles inlesioned males remains unaffected by the CCS lesion.

The following hypotheses should help to explain the alterations seen in lesionsongs.

(1) Since the development of the muscular power for the closing movement isunaffected, the changes described in iii must be caused by alterations in the forcesthat are orthogonal to the file and to the wing surface. These will be labelled'engaging forces'. Engaging forces that are too high would thus result in 'sticking',while forces that are too low would either cause 'slipping' or 'overspeed'. The conceptof slipping caused by insufficient engaging force is evident. The sticking due toexcess engaging forces can only occur if the form of the file teeth and plectrum aresuch that effective locking is possible, as in a ratchet. Scanning micrographs showthat the teeth and plectrum profiles are in fact adequate to produce locking(Schaffner, 1985; G. Breutel, personal communication).

(2) Using postural muscles, which may be tonically active, or asymmetries inthe excitation of the major muscles (see Kutsch, 1969), the cricket could adjust theengaging pressure such that sliding as well as sticking are avoided, and optimumoperation of the clockwork mechanism is achieved.

This postulated control system needs two sensing elements, one measuring wingposition or velocity, such as the wing hinge stretch receptor and chordotonal organ,and the other measuring thrust along the file (closing force), such as the CCS. Theaim of this control loop would be to apply as high closing forces as possible (avoidingsliding), while keeping the wings in motion (avoiding sticking). The result of thisaction would be a maximum sound power output p, which depends on closingvelocity v and closing force f in the following way: p = f X v. Here, v need not bemeasured with precision as long as it is not zero, since the clockwork mechanism

38 K. -H. SCHAFFNER AND U. T . KOCH

regulates v automatically. In such a system, the removal of the force transducerwould cause the control loop to increase the engaging forces, since 'sliding' issignalled by 'no closing force' information. The primary result would then besticking, which would be sensed by the movement detector and cause the system toreduce engaging pressure, resulting in 'slipping'.

The hypotheses outlined above should predict disturbances if the movement-sensing elements (stretch receptor and chordotonal organ) were removed from thesystem. Moss (1971) reported no changes in the song pattern when he removedthe stretch receptor. This is not necessarily a contradictory result, since Moss left thechordotonal organ intact, which may have led to a situation similar to the one-sidedlesions of the CCS: one of the two sensory systems keeps up the system's perform-ance to a large extent. In addition, Moss (1971) looked for changes of the songpattern only at the level of the EMG signals which we have shown to be unaffectedeven during severe disturbances of the sound output.

A closer inspection of the proposed feedback system raises several questions.(1) Reaction time. Since the syllable duration is only 15 ms and the sensory

information from the CCS and the velocity sensors is spread over the syllableduration, it seems unlikely that the feedback loop could correct wing engaging forceswithin the same syllable. Rather, we assume that the sensory information is inte-grated and stored for the adjustment of engaging forces in the next cycle, in a waysimilar to the position-control system of the postcubital hair fields (Elliott, 1983).

(2) Generation of engaging forces. Preliminary experiments with an isolatedwing—thorax preparation (U. T. Koch, unpublished results) show that a torquearound the longitudinal axis of the tergal plate can generate the engaging forces. Sucha torque could be generated by the slight asymmetries in the timing between left andright closer muscles, as observed by Kutsch & Huber (1970). As in locust steeringreactions (Zarnack & Mohl, 1977), information from the sensory systems could beused to change the muscle timing and thus change the engaging forces. The results ofKutsch (1969) seem to contradict this scheme. He showed that the cricket was stillcapable of singing when all wing muscles on one side had been cut or denervated,demonstrating the very strong coupling between both sides of the thorax.

A further interesting candidate for the generation of engaging forces is M85. In thelocust, M85 has been shown to produce wing twisting leading to pronation (Pfau,1983), which may be analogous to the wing twist required to generate engagingforces. In addition, a reflex connection between campaniform wing sensilla and M85was found (Heukamp, 1983; Wendler & Heukamp, 1983). Light microscopicobservations in the cricket (Schaffner, 1985) showed that cubital nerve projectionsend in an area of the mesothoracic ganglion which is occupied by ramifications ofM85. This supports the idea that a reflex connection between M85 and the CCSmay exist. However, because of the lack of knowledge about the precise functionalmorphology of the cricket wing hinge, the ideas about the role of M85 or othermuscles in the generation of engaging forces must remain speculative.

The influences of wing sensory systems described here stabilize the sound outputof the singing cricket in such a way that sound pulses of homogeneous quality are

Cricket stridulation 39

reliably produced, thus transforming the very stable basic motor spike patterninto an equally stable sound pattern. The results of the phonotaxis experiments(Schaffner & Koch, 1987) underline the biological relevance of this control system.Male crickets without information from the cubital campaniform sensilla producefaulty calling songs and have a much reduced success in luring females for mating.

We gratefully acknowledge the support and constant interest of Professor FranzHuber. Much help was offered by our fellow scientists in Huber Abteilung. We areespecially grateful to Chris Elliott, Theo Weber, Hans-Ulrich Kleindiest and GiinterKamper for their technical support and helpful discussions.

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patterns. Z. vergl. Physiol. 62, 267-283.ELEPFANDT, A. (1980). Morphology and output coupling of wing muscle motoneurons in the field

cricket (Gryllidae, Orthoptera). Zool. jfb. Physiol. 84, 26-45.ELLIOTT, C. J. H. (1983). Wing hair plates in crickets: physiological characteristics and

connections with stridulatory motor neurones. X exp. Biol. 107, 21-47.ELLIOTT, C. J. H. & KOCH, U. T. (1983). Sensory feedback stabilizing reliable stridulation in

Gryllus campestris L. Anitn. Behav. 31, 887-902.ELLIOTT, C. J. H. & KOCH, U. T. (1985). The clockwork cricket. Naturwissenschaften 72,

150-152.EwiNG, A. & HOYLE, G. (1965). Neuronal mechanisms underlying control of sound production in

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