Variability of vibratory signals and mate choice selectivity in the southern green stink bug.

The southern green stink bug, Nezara viridula, has a complex mate recognition system that implicates chemical and acoustic signals. To localise a sexual partner acoustically, a male and female alternate between the male courtship song (MCrS) and the female calling song type 1 (FCS1). Although previous research has revealed that both signals show geographical variability, until now no studies have explored the form of this variability. We analysed the temporal and spectral characteristics of MCrS and FCS1 pulse trains of males and females from a French and a Guadeloupe population. Pulse train duration of the MCrS varied within and between populations. Likewise, spectral and temporal parameters of FCS1 varied within and between the two populations. Although females did not show any behavioural responses to pre-recorded MCrS, males responded to pre-recorded FCS1 by emitting a higher number of MCrS per minute. Furthermore, males modulated the repetition rate of their MCrS pulse trains to match those of the FCS1. All males responded to FCS1 from French and Guadeloupe females despite the temporal differences in these songs; however, they responded with a shorter latency and a higher rate of MCrS/FCS1 pulse trains to the songs of females from their own population. In choice experiments with two alternatives, responses to FCS1 were inhibited when males received a simultaneous female call from another Pentatomidae sympatric species, Acrosternum hilare. We conclude that, although males prefer FCS1 from their own population, they recognise FCS1 from French and Guadeloupe N. viridula females as species-specific female calls. Variability of vibratory signals might play a role in mate choice.

Directional sensitivity of wind-sensitive giant interneurons in the cave cricket Troglophilus neglectus.

Unlike the situation in most cockroach and cricket species studied so far, the wind-sensitive cerci of the cave cricket Troglophilus neglectus Krauss (Rhaphidophoridae, Orthoptera) are not oriented parallel to the body axis but perpendicular to it. The effects of this difference on the morphology, and directional sensitivity of cercal giant interneurons (GIs), were investigated. In order to test the hypothesis that the 90 degrees change in cercal orientation causes a corresponding shift in directional sensitivity of GIs, their responses in both the horizontal and vertical planes were tested. One ventral and four dorsal GIs (corresponding to GIs 9-1a and 9-2a, 9-3a, 10-2a, 10-3a of gryllid crickets) were identified. The ventral GI 9-1a of Troglophilus differed somewhat from its cricket homologue in its dendritic arborisation and its directional sensitivity in the horizontal plane. The morphology and horizontal directionality of the dorsal GIs closely resembled that of their counterparts in gryllids. In the vertical plane, the directionality of all GIs tested was similar. They were all excited mainly by wind puffs from the axon-ipsilateral quadrant. The results suggest that directional sensitivity to air currents in the horizontal plane is maintained despite the altered orientation of the cerci. This is presumably due to compensatory modifications in the directional pReferences of the filiform hairs.

Songs of Holcostethus strictus (Fabricius): a different repertoire among landbugs (Heteroptera: Pentatomidae).

Songs emitted during mating by male and female Holcostethus strictus were recorded as substrate vibrations. Spectra of the vibrational signals have a dominant frequency peak between 100 and 260 Hz and in this respect reflect the general characteristic of the family Pentatomidae. Songs of H. strictus differ from the song repertoire of the southern green stink bug Nezara viridula (L.) (Pentatomidae) in many respects. The female calling and courtship songs differ in echeme and phrase duration. The male calling song is composed of spectrally different subunits. The male courtship song is characterised by three types of spectrally and temporally different echemes. The male copulatory song is composed of echemes of two types, which constitute a phrase of less regular temporal structure. In H. strictus, males start to sing first and female songs are less complex than in N. viridula. The female calling song is evoked by male calling and does not trigger male response. The female and male courtship song phrases are superimposed on one another and we have not observed any obvious regularity in their exchange. The possible role of different songs in H. strictus is discussed and compared with that in other pentatomide landbug species.

Temporal and spectral properties of the songs of the southern green stink bug Nezara viridula (L.) from Slovenia.

Substrate born songs of the southern green stinkbug Nezara viridula (L.) from Slovenia were recorded and analysed. The male calling song is composed of narrow-band regularly repeated single pulses and of broad-band frequency modulated pulses grouped into pulse trains. The female calling song is characterised by broad-band pulsed and narrow-band non-pulsed pulse trains. A frequency modulated pre-pulse precedes the narrow-band pulse train. A frequency-modulated post-pulse usually follows the pulse train of the male courtship song. The male calling song triggers broad-band pulse trains of the female courtship song. The female also produces a repelling low-frequency vibration that inhibits male calling and courtship. The male rival song is characterised by prolonged pulses with a typical frequency modulation.

Green stink bug Nezara viridula detects differences in amplitude between courtship song vibrations at stem and petiolus.

Green stink bug Nezara viridula courtship songs are transmitted through plants as substrate vibrations. The amplitude of the vibrations is different at different distances from the source of vibration and at different locations on the plant. Amplitudes of the local vibration were measured on stem and petioli of the bean plant (Phaseolus vulgaris) with a Laser-Doppler vibrometer. Differences of the amplitudes of vibration between adjacent points around the nodes were large enough to release differential nerve activities of vibration receptor cells of different legs. There was no correlation between the signal amplitude and the distance from the singing bug, however; the differences in amplitudes of vibrations between the stem and the adjacent petioli of leaves potentially permitted direction finding in the green stink bug males.

Vibratory songs of hybrids from Brazilian and Slovenian populations of the green stink bug Nezara viridula.

Males and females of the green stink bug Nezara viridula produce species and sex specific vibrational signals. The songs of bugs from geographically isolated population differ in their temporal characteristics. Hybrids were produced between the bugs from Brazilian and Slovenian populations in order to examine the levels of genetic inheritance of their vibratory songs. Hybrid males and females produced songs which are distinctly different from parental songs and these differences can be attributable to genetic factor. The results show that in some parameters the hybrid songs are intermediate between the parental types. Several song parameters are apparently sex-linked. It remains to be established whether observed genetically determined differences in vibratory songs also indicate that cryptic species exist within the taxon N. viridula.

Vibrational directionality in the southern green stink bug, Nezara viridula (L.), is mediated by female song.

We tested the hypothesis that male southern green stink bugs, Nezara viridula (L.), use substrate-borne songs to locate females. We recorded the responses of bugs on plants to the vibrations caused by a prerecorded female song and by an artificial sound. The female song caused males to walk, to respond with the calling and courtship songs and to approach the source of the song with characteristic search behaviour at junctions between branches on the plants. At a junction, a searching male stopped, stretched his legs and antennae and compared the vibratory signals on the two branches, with different combinations of legs and antennae. The males then left the junction and approached the source of the vibration. Males located the loudspeaker significantly more frequently in the presence than in the absence of vibratory stimuli on cyperus, Cyperus alternifolius L., and beans, Phaseolus vulgaris L. Vibrational directionality was also elicited by artificial pure tones whose spectral and temporal parameters were similar to those of natural female song. Females showed no reaction to vibratory stimulation and no vibrational directionality. We discuss possible mechanisms underlying vibrational directionality in the light of expected signal changes during transmission through plants. Copyright 1999 The Association for the Study of Animal Behaviour.

Mechanoreceptors in insects: Johnston's organ in Nezara viridula (L) (Pentatomidae, Heteroptera).

Behavioural observations of Nezara viridula suggested that the antennae could be involved in detecting the substrate vibrations important in intraspecific communication of these insects. Therefore the vibrosensitive properties of Johnston's organ, a mechanoreceptor sensitive to the movements of the antennal flagellum relative to pedicel, were investigated. Vibrational stimuli were applied to the proximal flagellar segment where activity in the antennal nerve was recorded via a tapered tungsten electrode inserted into the second antennal segment where Johnston's organ is located. Sensory cells of Johnston's organ scolopidia respond to low frequency substrate vibrations (below 200 Hz). Both fast and slowly adapting receptor cells are present. However, the sensitivity of Johnston's organ to substrate vibrations in Nezara viridula is much lower than that of vibroreceptors in their legs which are known to be involved in intraspecific vibrational communication.

Differences in vibratory sound communication between a Slovenian and an Australian population of Nezara viridula (L.) (Heteroptera: Pentatomidae).

Sound communication, by means of substrate-borne vibrations, was recorded and analysed from a Slovenian and Australian population of the pentatomid landbug, Nezara viridula. Mate location and short-range courtship in N. viridula involves the recognition of such species-specific signals and responding appropriately to them. Temporal parameters of all N. viridula song types differed considerably between males and females of the two populations. In particular, the female calling song, which enables Slovenian male bugs to locate the female on a host plant, was significantly different. The song repertoire from a Slovenian and Australian population and the species status of N. viridula are discussed.

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. © 1995 Wiley-Liss, Inc.