Acoustic defence in an insect: characteristics of defensive stridulation and differences between the sexes in the tettigoniid Poecilimon ornatus (Schmidt 1850)

Many insects exhibit secondary defence mechanisms upon contact with a predator, such as defensive sound production or regurgitation of gut contents. In the tettigoniid Poecilimon ornatus, both males and females are capable of sound production and of regurgitation. However, wing stridulatory structures for intraspecific acoustic communication evolved independently in males and females, and may result in different defence sounds. Here we investigate in P. ornatus whether secondary defence behaviours, in particular defence sounds, show sex-specific differences. The male defence sound differs significantly from the male calling song in that it has a longer syllable duration and a higher number of impulses per syllable. In females, the defence sound syllables are also significantly longer than the syllables of their response song to the male calling song. In addition, the acoustic disturbance stridulation differs notably between females and males as both sexes exhibit different temporal patterns of the defence sound. Furthermore, males use defence sounds more often than females. The higher proportion of male disturbance stridulation is consistent with a male-biased predation risk during calling and phonotactic behaviour. The temporal structures of the female and male defence sounds support a deimatic function of the startling sound in both females and males, rather than an adaptation for a particular temporal pattern. Independently of the clear differences in sound defence, no difference in regurgitation of gut content occurs between the sexes.     

Structure and evolution of stridulatory mechanisms in New Zealand wetas (Orthoptera : Stenopelmatidae)

Four types of stridulatory mechanisms were found in 35 species (7 genera) of New Zealand wetas (Orthoptera : Stenopelmatidae). These include: (1) tergo-femoral; (2) tergo-tergal; (3) mandbbuao-mandibular; and (4) pleuro-coxal. These fell into 12 groups, based upon shape, density and pattern of tergal and femoral pegs, number of terga bearing pegs and presence of mandibular tusks bearing stridulatory tubercles. The plesiomorphic condition, consisting of spinose peg patches on 3 or more abdominal tergites rubbed by bands of pegs on the femur, is found in Hemiandrus spp. Apomorphically-derived tergal files have arisen separately in 3 other genera. In Hemideina, (2 species groups) well-formed files are very similar among species. In Deinacrida, (4 species groups), the trend is toward file reduction into one or 2 massive tergal ridges, and embellished femoral pegs. In the tusked wetas (2 gen., 2 spp.), one species has a crude file of many broken ridges. Stridulatory structures on mandibular tusks of both New Zealand species are unique, although the tusks appear to have their origin in African stenopelmatids. The plesiomorphic condition appears to have been deployed originally for defense stridulation (inter-specific communication). Additional intea-specific stridulatory communication developed in Hemideina and Deinacrida, using the apomorphic file and peg mechanisms. Here, the stridulation is associated with defense, calling, mating and disturbance behaviors.     

Consistency of females’ stridulatory behaviour during inter‐sexual interactions in spiders

In a sexual context, it is expected that females base their choice of mate on the behaviours that males perform during courtship, as such behaviours are associated with the male's mate quality. Stridulation is one form of female communication in arthropods, for example, spiders. In spiders, stridulation during sexual interactions is relatively common in some groups but mainly restricted to males. In the pholcid spider Holocnemus pluchei (Pholcidae), both sexes have stridulatory organs. The aims of the present work were to: (a) determine possible differences in the frequency of occurrence of stridulation between females during inter‐sexual interactions, (b) establish female consistency in stridulation along repeated interactions and (c) analyse if female stridulation is associated with certain male behaviours during pre‐copulatory courtship and with male size. Female H. pluchei showed highly repeatable differences in their frequency of stridulation across consecutive encounters with males (ICC = 0.64). However, only a modest level of repeatability was detected in total time females spent stridulating across trials (ICC = 0.19). Females’ mean stridulatory behaviour did not change across ten consecutive trials spread across 20 days, and their behaviour was apparently unaffected by male persistence of copulatory attempted and/or size. These results imply that the frequency of female stridulatory behaviour is a trait that is highly characteristic of each individual. Finally, our work opens the door to determine whether behavioural consistency manifests in other ecological contexts and their functional implications.     

The complex stridulatory behavior of the cricket Eneoptera guyanensis Chopard (Orthoptera: Grylloidea: Eneopterinae)

Crickets produce stridulated sounds by rubbing their forewings together. The calling song of the cricket species Eneoptera guyanensis Chopard, 1931 alternates two song sections, at low and high dominant frequencies, corresponding to two distinct sections of the stridulatory file. In the present study we address the complex acoustic behavior of E. guyanensis by integrating information on the peculiar morphology of the stridulatory file, the acoustic analysis of its calling song and the forewing movements during sound production. The results show that even if E. guyanensis matches the normal cricket functioning for syllable production, the stridulation involves two different closing movements, corresponding to two types of syllables, allowing the plectrum to hit alternately each differentiated section of the file. Transition syllables combine high and low frequencies and are emitted by a complete forewing closure over the whole file. The double-teeth section of the stridulatory file may be used as a multiplier for the song frequency because of the morphological multiplication due to the double teeth, but also because of an increase of wing velocity when this file section is used. According to available phylogenetic and acoustic data, this complex stridulation may have evolved in a two-step process.     

Stridulation and Courtship Behaviour of Four Endemic Pill-Millipedes, <Emphasis Type="Italic">Arthrosphaera</Emphasis> spp. (Sphaerotheriida: Arthrosphaeridae) of the Western Ghats of India

Mating behaviour of four species of pill-millipedes under genus Arthrosphaera Pocock (Arthrosphaera dalyi Pocock and Arthrosphaera disticta Pocock, Arthrosphaera fumosa Pocock and Arthrosphaera magna Attems) endemic to the Western Ghats of Southern India was analyzed in mesocosms. Stridulation is a classical communication signal in males as well as females for mate selection. Conglobation (or volvation) is a mechanism of defence to protect from disturbance or avoid predation. If male touches female or vice versa they conglobate. To avoid disparity among individuals of the same species, volvating pill-millipedes evolved stridulation behaviour for communication. The male broadcasts appropriate signal to female through stridulation to advertise its interest in mating. The females test the male’s fitness by conglobation and suitable male uncoils the partner through stridulation signals. Male with its pygidium successfully uncoils the female and attains suitable orientation for courtship. Male pairs with female ventro–ventro contact in opposite direction to deposit sperm into the vulva of female. The duration of mating varies from species to species and usually a lapse from 3 to 30 min. Vibration generated by stridulation is species-specific and its perception mechanism in pill-millipedes is yet to be clearly understood. Present study emphasized the structure of stridulatory organs, mechanism of stridulation and pattern of mating behaviour in four species of pill-millipedes.     

Calling behavior in bushcrickets of the genusPoecilimon with differing communication systems (Orthoptera: Tettigonioidea,Phaneropteridae)

In bushcricket communication systems males have to signal acoustically to attract females. The calling activity, however, not only may increase mating success, but also may result in costs in terms of energy and predation risks. In this study the calling activity of males and its timing during the day were analyzed for several species of the genus Poecilimon,representing two different communication systems. In species with mute females that approach the males phonotactically, calling was restricted to darkness and syllable rates were high. In species where females respond acoustically to male song and thus can induce the male to approach them phonotactically, males called during both day and night or during the day only, and syllable rates were low. After mating, male acoustic activity dropped to a very low level but was restored during the following 2 to 3 days, a time period longer than the minimal male mating interval. The results are discussed with regard to possible energetic limitations, the risk of attracting predators and parasitoids, and the spermatophore production of males.     

Pharmacological brain stimulation releases elaborate stridulatory behaviour in gomphocerine grasshoppers – conclusions for the organization of the central nervous control

Grasshoppers produce a variety of sounds generated by complex movements of the hindlegs. Stridulation, performed in the context of partner finding, mating and rivalry, can be released by pressure injection of cholinergic agonists into the protocerebrum. Particularly stimulation with muscarinic agonists induced long-lasting stridulation that resembled the natural behaviour to an astonishing degree, not only with respect to their temporal structure and right/left coordination, but also to changes in the song sequences according to the progress of courtship stridulation, even including accessory movements of other parts of the body. According to the complexity of their stridulatory behaviour ten gomphocerine species were chosen for this comparative study. The results indicate that the protocerebrum fulfils two important tasks in the control of stridulation: (1) it integrates sensory input relevant to stridulation that represents a certain behavioural situation and internal state of arousal, and (2) it selectively activates and deactivates the thoracic networks that generate the appropriate movement and sound patterns. With the knowledge of the natural behaviour and the accessibility to pharmacological and electrophysiological studies, the cephalic control system for stridulation in grasshoppers appears to be a suitable model for how the brain selects and controls appropriate behaviours for a given situation.     

Signalling and Sexual Conflict: Female Spiders Use Stridulation to Inform Males of Sexual Receptivity

The use of acoustic signals by males during courtship and mating is well known. Nevertheless, their association with female unwillingness to mate is much less studied. In spiders, stridulation during sexual interactions is relatively common in some groups, but mainly restricted to males. In the pholcid spider Holocnemus pluchei, both sexes have stridulatory organs. The aims of the present work were (1) to establish whether female stridulation occurs during intra‐ and inter‐sexual interactions, (2) to determine whether female reproductive status affects the likelihood that she will stridulate and (3) to determine whether female stridulation is influenced by male sexual behaviour. We found that female stridulation usually occurs both during intrasexual interactions and, most frequently, during intersexual interactions. Females with more previous matings stridulated more frequently. Stridulation intensity was higher in females that did not accept new copulations compared with those that copulated. Female stridulation did not vary in elaborated and non‐elaborated courtship. Thus, females use stridulation to communicate levels of sexual receptivity. It is also possible that females use stridulation to indirectly assess male ability to persist and persuade.     

Unusual abdomino-alary,defensive stridulatory mechanism in the bushcricket Pantecphylus cerambycinus (Orthoptera,Tettigonioidea, Pseudophyllidae)

The bushcricket Pantecphylus cerambycinus has two types of stridulatory mechanisms and acoustical signals. The elytro-elytral mechanism typical for tettigonioid bushcrickets is used to produce a narrow-band calling song (peak frequency 15 kHz). An abdomino-alary mechanism is used for disturbance stridulation. Its stridulatory file is situated on the hind edge of the abdominal tergites and consists of 50-70 parallel ridges, covering the whole width of the tergite. The broad-band sound (peak frequency 10 kHz) is produced by the contact between the file and ribs situated on the upper side of the hindwings which are folded in such a way that their upper side is directed toward the tergites. Defensive stridulation in bushcrickets is reviewed here, and its function and evolution discussed in the context of predator avoidance strategies. © 1996 Wiley-Liss, Inc.     

Variance in female responses to the fine structure of male song in the field cricket, Gryllus integer

Although female mating preferences are a focus of current controversy,little detailed information exists on female preferences withinnatural populations. In the field cricket Gryllus integer, malecalls attract sexually receptive females, and females preferentiallymove toward male calls with longer calling bouts (periods ofcalling containing no pause greater than 0.10 s in real time).This study investigated female preferences for other variablesof the male song, including syllable period, chirp pause, andnumber of syllables per chirp. Male song was measured in thefield to determine mean values for each variable in nature.Female preferences were determined using a locomotor-compensatordevice, on which females ran in response to sequential playbacksof synthesized male song. Mean female preferences correspondedroughly to mean male song variables. Nonetheless, females variedgreatly in their responses to synthesized calls differing insyllable period, syllable number, and chirp pause. Moreover,individual females who were more selective for any one variablealso tended to be more selective for others. These results showthat females may differ from one another in their mating preferencesand degrees of selectivity, even within a single population.     

Stridulatory pattern generation in acridid grasshoppers: metathoracic interneurons in Stenobothrus rubicundus (Germar 1817)

Stridulation was elicited in tethered gomphocerine grasshoppers of the species Stenobothrus rubicundus in order to identify interneurons of the stridulation pattern generator, and describe their morphological and physiological properties. Nine types of such neurons could be found and characterized; eight of those could additionally be compared to corresponding neuron types previously known from other species. As shown in detail for one selected type, the neurons of the stridulation pattern generator are very similar in their anatomical appearance, and possess similar physiological qualities at least in two species with similar stridulation patterns. Stridulation interneurons of species with largely different stridulatory motor patterns have a similar morphology, but show a different activation timing throughout the stridulation. Nevertheless, special properties such as resetting or initiation capability of certain stridulation interneurons seem to be conserved throughout the species. The results suggest that the stridulation pattern generator of different species consists of a uniform set of interneurons that change their activity pattern to produce species-specific song movements.     

Abdominal ventilatory pattern in crickets depends on the stridulatory motor pattern

Abstract. Ventilatory motor patterns were recorded from abdominal muscles in crickets, Gryllus campestris L.and Teleogryllus commodus (Walker), at rest and during three types of stridulatory motor activity; calling, courtship and aggressive song.
Increases in ventilatory period were almost exclusively due to an increase of the pause between expiratory bursts, whereas abdominal ventilatory bursts remained constant at 200 ms.Ventilatory patterns depended on the stridulatory motor pattern and indicated that the same basic respiratory oscillator exists in both cricket species.
In G.campestris there was a strict 1:1 coupling between chirps and ventilatory bursts.In T.commodus such a relationship was also observed for the chirp part of the songs, but less strictly for the trill part of the calling song and not for the courtship song.In both species the onset of the ventilatory burst was within ± 100 ms of a stridulatory chirp.Ventilatory burst lasted longer the earlier they began before a stridulatory chirp.This suggests strongly that the stridulatory motor pattern terminates the expiratory burst, and thus influences the ventilatory motor pattern.     

Temperature coupling in cricket acoustic communication

Acoustic communication in Gryllus firmus is temperature-coupled: temperature induces parallel changes in male calling song temporal pattern, and in female preference for song. Temperature effects on song production and recognition networks were localized by selectively warming head or thorax or both head and thorax of intact crickets, then eliciting aggression song production (males) or phonotaxis to synthetic calling song (females). Because male song is produced by a thoracic central pattern generator (CPG), and because head ganglia are necessary for female song recognition, measurements of female phonotaxis under such conditions may be used to test the following competing hypotheses about organization of the song recognition network: 1. A set of neurons homologous to the male song CPG exist in the female, and are used as a template that determines preferred values of song temporal parameters for song pattern recognition (the common neural elements hypothesis), and 2. temporal pattern preference is determined entirely within the head ganglia. Neither selective warming of the head nor of the thorax was effective in changing female song preference, but simultaneous warming of head and thorax shifted preference toward a faster song in most preparations, as did warming the whole animal by raising ambient temperature. These results suggest that phonotactic preference for song temporal pattern is plurisegmentally determined in field crickets. Selective warming experiments during aggression song production in males revealed that syllable period is influenced but not completely determined by thoracic temperature; head temperature is irrelevant. The song CPG appears to receive some rate-setting information from outside the thoracic central nervous system.     

Colony Wide Behavioral Contexts of Stridulation in Imported Fire Ants (Solenopsis invicta Buren)

Red imported fire ants, Solenopsis invicta, possess stridulatory organs and stridulate in a variety of contexts. We used a stethoscope mounted microphone to study stridulation at the colony level in the context of emigration, disturbance, and excavation. In conjunction with preliminary observations of nest and foraging activities, our results suggest stridulation serves multiple functions in S. invicta. Stridulation was not significantly increased in colonies during responses to disturbance, and only marginally during colony emigration. Colonies involved in excavation, however, exhibited a significant increase in stridulatory activity. Four possible explanations for the function of stridulation in this context are discussed in relation to the stridulatory behavior of individuals, solitary wasps, and published literature on formicid stridulation.     

Recognition of sex in the acoustic communication of the grasshopper Chorthippus biguttulus (Orthoptera, Acrididae)

Many gomphocerine grasshoppers communicate acoustically: a male's calling song is answered by a female which is approached phonotactically by the male. Signals and recognition mechanisms were investigated in Chorthippus biguttulus with regard to the cues which allow sex discrimination. (1) The stridulatory files on the hindfemur of both sexes are homologous in that they are derived from the same row of bristles, but convergent with respect to the “pegs”. In males the pegs are derived from the bristles, and in females from the wall of the bristle's cup. (2) Male and female songs are generated by similar, probably homologous motor programs, but differ in the duration, intensity, “gappyness” of syllables, risetime of pulses, and the frequency spectra. The hindleg co-ordination during stridulation and the resulting temporal song patterns are less variable in males than in females. (3) For both sexes, recognition of a mate's signal depends on species-specific syllable structure. For males it is essential that the female syllables consist of distinct short pulses, whereas females reject “gappy” syllables. Males strongly prefer “ramped” pulses, females respond to syllables irrespective of steeply or slowly rising ramps. Males react only to the low-frequency component, whereas females prefer spectra containing both, low and high frequency components. Accepted: 20 November 1996     

Auditory information processing in stridulating grasshoppers: tympanic membrane vibrations and neurophysiology

During stridulation in the gomphocerine grasshopper Omocestus viridulus the leg movements, sound pattern and either summed auditory nerve activity or single interneuron activity were recorded. Simultaneous laser interferometric and vibrometric measurements of the displacement and velocity of the tympanic membrane were performed at the pyriform vesicle (d-receptor group). Slow displacements of the tympanic membrane occur in phase with the ventilatory and stridulatory rhythm and reach 10 m_peak-peak and 1–3 m_peak-peak in amplitude, respectively. Additionally, the tympanic membrane oscillates maximally in the range 5–10 kHz. These high-frequency oscillations are due to sound production and motor activity and correspond in amplitude to oscillations evoked by sound pressures of 90-dB SPL. They activate the auditory receptors during most of the stridulatory cycle even during mute stridulation. Only at the lower reversal point of the leg movement are membrane vibrations and receptor activity at a minimum. As a consequence the response of receptors and interneurons to auditory stimuli are generally impaired and an auditory response of receptors and interneurons can be elicited only during a short period at the lower reversal point. Although in this phase of the stridulatory cycle auditory sensitivity is present, males do not show phonotactic responses towards female songs during ongoing own stridulation.     

Locomotory and stridulatory circadian rhythms in the cricket, Teleogryllus commodus

Male crickets of the species Teleogryllus commodus express circadian rhythms in both their stridulatory and locomotory behaviours. Both forms of activity show the same free-running period (τ) in either DD (23·4 hr) or LL (25·1 hr). Although some overlap is seen between periods of locomotion and stridulation, the majority of each activity is found in different phases of the circadian cycle: locomotion occurs mainly in the subjective day and stridulation in the subjective night. Entraining LD cycles with photoperiods of 12 hr produce exogenous effects that can obscure endogenous components of the rhythms. Red light (λ>600 nm) causes the period to lengthen and RD cycles can entrain both rhythms. Single white light pulses of 2 or 6 hr did not produce significant phase shifts, but did cause τ to shorten when given in the subjective night. The significance of these observations is discussed. Given the results obtained to date, it is not likely that each rhythm is under the control of a separate circadian pacemaker.