Tree wetas (Hemideina crassicruris) (Orthoptera: Stenopelmatidae) of Stephens Island,Cook Strait

Abstract

Tree wetas (Hemideina crassicruris) were studied in kohekohe (Dysoxylum spectabile) forest on Stephens Island, Cook Strait, between 5 and 17 January 1978. Mark and recapture observations suggested a population density of at least 5300 wetas ha^?1 and a biomass of 42 kg ha^?1. Activity of wetas increased with temperature and humidity. Tuataras are important predators on Stephens Island and probably deter wetas from moving onto the forest floor. The enlarged head and jaws of male wetas are associated with head-on fights for occupancy of galleries. Single, adult males occupy galleries with a harem of up to 9 females. Stridulation was associated with agonistic encounters and was most frequent shortly before dawn. Seventeen percent of males and 42% of females were damaged. Moulting, copulation, and oviposition were observed, and females carried up to 96 mature eggs. Stephens Island tree wetas reach larger sizes overall, and males have relatively larger heads, than in other populations of the Cook Strait region. The number and size of galleries and the presence or absence of predators may be important determinants of weta population density, sex ratio, harem formation, and activity on the ground.     

Novel use of hair sensilla in acoustic stridulation by New Zealand giant wetas (Orthoptera: Anostostomatidae)

Sound production in New Zealand giant wetas (Orthoptera: Anostostomatidae) includes a femoro-abdominal mechanism, a ticking sound when alarmed (mechanism unknown) and, in two species (Deinacrida rugosa and Deinacrida parva), a tergo-tergal mechanism on the dorsal overlapping surfaces of abdominal tergites. The tergo-tergal mechanism consists of bilaterally paired patches of short curved spines on the dorsal anterior margins of tergites II–V, rubbed by opposing patches of articulated hair sensilla on the underside of each overlapping tergite. The latter are extremely robust, modified mechanoreceptors inserted at an acute angle onto raised bases which greatly restrict movement. They rub sideways against the underlying spines and produce sound during telescopic abdominal contraction which accompanies defence leg kicking stridulation. Movement analysis showed that the abdominal tergites contract asynchronously during stridulation. Sound is produced during both phases of telescoping. Femoro-abdominal sound comprises loud clicks of broadband sound principally below 10 kHz; tergo-tergal sound is a softer hiss spreading broadly from 10 kHz to the ultrasonic above 20 kHz. We propose that the tergo-tergal mechanism may have evolved under predation pressure by the ground gleaning short tailed bat endemic to New Zealand. The use of mechanosensory hair sensilla for sound production is rare in arthropods.     

Communication by substratum vibration in the New Zealand tree weta, Hemideina femorata (Stenopelmatidae: Orthoptera)

The propagation of vibrations along the trunk and branches of a manuka tree, generated in response to the impact of a steel ball-bearing on the trunk, was measured with an accelerometer. The impact generated bending waves which travelled along the trunk and into the branches. Close to the point of impact the waveform was dominated by a damped oscillation at 518 Hz; as the bending wave progressed away from the point of impact the frequency of the dominant waveform increased. Beyond 200 cm the waveform became increasingly complex and a smallamplitude, high-frequency component progressively preceded the main wave. Branching points also induced complex waveforms, particularly where branches lay at a large angle to the trunk. Stridulating wetas also generated bending waves in the tree at a frequency close to that generated by the ball-bearing, as well as at a higher frequency of 7.5 kHz. The acoustic frequency of stridulation peaked at 0.8 and 3.4 kHz. Records from nerves serving the vibration-sensitive subgenual organs showed that wetas can detect oscillations at 1 kHz at 0.015ms^-2. A stridulating weta placed on the same log as a preparation in which the nerve from the subgenual organ was monitored generated oscillatins well above the threshold for detection.     

中国蟋螽亚科二新种(直翅目:沙螽科)

记述蟋螽亚科2新种,少刺荒栖蟋螽Eremus parvospinus sp.nov.采自广西,黑膝疾蟋螽Apotrechus nigrigeniculatus sp.nov.采自四川。模式标本保存在中国科学院上海植物生理生态研究所昆虫标本馆。     

Avoidance of intracellular freezing by the freezing-tolerant New Zealand Alpine weta Hemideina maori (Orthoptera: Stenopelmatidae)

Calorimetric analysis indicates that 82% of the body water of Hemideina maori is converted into ice at 10 degrees C. This is a high proportion and led us to investigate whether intracellular freezing occurs in H. maori tissue. Malpighian tubules and fat bodies were frozen in haemolymph on a microscope cold stage. No fat body cells, and 2% of Malpighian tubule cells froze during cooling to -8 degrees C. Unfrozen cells appeared shrunken after ice formed in the extracellular medium. There was no difference between the survival of control tissues and those frozen to -8 degrees C. At temperatures below -15 degrees C (lethal temperatures for weta), there was a decline in survival, which was strongly correlated with temperature, but no change in the appearance of tissue. It is concluded that intracellular freezing is avoided by Hemideina maori through osmotic dehydration and freeze concentration effects, but the reasons for low temperature mortality remain unclear. The freezing process in H. maori appears to rely on extracellular ice nucleation, possibly with the aid of an ice nucleating protein, to osmotically dehydrate the cells and avoid intracellular freezing. The lower lethal temperature of H. maori (-10 degrees C) is high compared to organisms that survive intracellular freezing. This suggests that the category of 'freezing tolerance' is an oversimplification, and that it may encompass at least two strategies: intracellular freezing tolerance and avoidance.     

Microclimate and variations in haemolymph composition in the freezing-tolerant New Zealand alpine weta Hemideina maori Hutton (Orthoptera: Stenopelmatidae)

The microclimate in the habitat of the New Zealand alpine weta Hemideina maori is very variable with winter temperatures down to −6 °C under the rocks where the insects are found. Subfreezing temperatures may in winter prevail for up to 17 days but diurnal cycles of freezing and thawing are common, as is also the case in summer. Rates of temperature change can be very high and up to −7.20 °C/h. During winter, humidity was high for extended periods ranging from 70% to 100% relative humidity (RH). In the summer, humidity ranged from 30% RH during the day to 100% RH at night. The supercooling point of the haemolymph was approximately −8 °C year round, caused by a heat labile substance. The supercooling point of the haemolymph of an insect of the same genus, Hemideina femorata not regularly exposed to subfreezing temperatures, was ca. −16.5 °C. Thermal hysteresis was not detected in the haemolymph of H. maori. Haemolymph osmolality varied from 380 mOsm (summer) to 700 mOsm (winter). Body water content was ca. 75% all year round. Total concentrations of sodium, potassium and chloride in haemolymph varied from 170 mM (winter) to 250 mM (summer). The total concentration of free amino acids varied from 58 mM (summer) to 263 mM (winter). This variation was mostly due to proline which varied from ca. 15 mM (summer) to ca. 100 mM (winter). The freeze-tolerant weta H. maori is exposed to a highly variable and cold environment all year round and several properties of its haemolymph composition can be attributed to these climatic conditions, e.g. the presence of ice-nucleating agents and an increase in the concentration of proline during cold hardening in the autumn. Accepted: 22 February 1999     

中国疾蟋螽属二新种记述(直翅目:沙螽科:蟋螽亚科)

记述了中国疾蟋螽属2新种,即指突疾蟋螽Apotrechus digitatus Liu et Bi,sp.nov.和近似疾蟋螽Apotrechus fallax Liu et Bi,sp.nov.。模式标本保存在中国科学院上海昆虫博物馆。     

Control systems models for the circadian clock of the New Zealand weta, Hemideina thoracica (Orthoptera: Stenopelmatidae)

The New Zealand weta, Hemideina thoracica, is a nocturnal orthopteran insect which emerges from holes in trees or from under bark soon after sunset to forage for several hours on plant and animal material before returning to its refuge before dawn. In tests of the internal clock hypothesis it exhibits clear circadian locomotor rhythms in which the period is initially somewhat less than 24 h, but frequently spontaneously increases to over 25 h. The rhythms are entrainable by light and temperature cycles, obey Aschoff's Law and are temperature compensated. A single oscillator feedback model accounts for these basic properties of the weta clock, but does not explain a variety of examples of rhythm lability, such as day skipping, spontaneous change in period, scalloping and desynchrony typically found in the real data. To account for these characteristics the model is expanded into two linked populations of oscillators, which retain the basic properties of the simple model and in addition interact through their coupling to show the various types of free-run lability. To make these control systems models compatible with the molecular interpretation of circadian biology, each of the components in the feedback loop is matched with molecular function and structure.     

Ice nucleation and freezing tolerance in New Zealand alpine and lowland weta, Hemideina spp. (Orthoptera; Stenopelmatidae)

Abstract.The alpine tree weta Hemidiena maori Pictet et Saussure (Orthoptera: Stenopelmatidae) is a large, flightless insect found above the treeline on many of the mountain ranges of the South Island of New Zealand. The population found on the Rock and Pillar Range, Central Otago has been identified as freezing tolerant with a haemolymph ice nucleating agent. The ability of H. maori to survive freezing is compared to the lowland weta Hemideina thoracica Walker and H. crassidens Blanchard, both of which are able to survive the formation of some ice in their bodies. Mortality is associated with time spent frozen in H. thoracica , and it is hypothesized that this species is killed when a critical proportion of its body water is frozen. All five subalpine and alpine populations of H. maori surveyed were found to be freezing tolerant.
Comparison of temperatures of first nucleation and mean supercooling point of haemolymph droplets suggest that haemolymph ice nucleating activity varies between populations of H. maori. Hemideina maori collected from the Mt Cook region appear to lack a haemolymph ice nucleator. This population is nevertheless freezing tolerant, suggesting that the haemolymph ice nucleating agent described in H. maori is not essential for freezing tolerance. Hemideina crassidens and H. ricta Hutton, both of which are found in lowland habitats, also had high mean supercooling point and temperatures of first nucleation of haemolymph droplets, suggesting that these species also have a haemolymph ice nucleator.
Comparison of ice nucleation characteristics of haemolymph and faecal material (representing gut contents) suggests that gut nucleators in H. maori may be at least as efficient as the haemolymph nucleator. It is concluded that freezing tolerance is probably not an adaptation to the alpine environment. This highlights the need for inter- and intraspecific comparative studies if physiological data are to be used to draw evolutionary conclusions.     

Structure of the cuticle of the alpine weta,Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae)

Sclerotized cuticle segments from the thorax, dorsal abdomen, and ventral abdomen of the alpine, weta Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae) were examined by light microscopy and by scanning and transmission electron microscopy. An epicuticle, exocuticle (outer and inner), mesocuticle, endocuticle, and deposition layer are present in transverse sections. The epicuticle is further composed of a cuticulin layer and inner epicuticle, the latter being finely laminated and containing narrow wax canals that terminate below the cuticle surface. Openings to dermal gland ducts are visible on the surface as are large setae and smaller sensory pegs. Frozen fractured cuticle reveals the presence of horizontal ducts or channels that run laterally within the cuticle. The structure of weta cuticle is compared with that of the common house cricket and arthropods in general.     

Diet of the ground weta Zealandosandrus gracilis (Orthoptera: Stenopelmatidae)

Abstract

The diet of the ground weta Zealandosandrus gracilis Salmon was investigated by examining the crop contents of 68 individuals collected throughout the year from the Cass area, Canterbury. Specimens representing all instars of both sexes, as well as adults, were obtained. Z. gracilis is carnivorous, preying on immature and adult invertebrates (mostly insects) of the forest litter. Similar prey was taken by early instars of both sexes; late instars captured a wider range of prey, including larger and more active species. Late-instar and adult females preyed more on adult insects such as mycetophilid flies than did males, which took more insect larvae.     

The scolopidial accessory organ in the Jerusalem cricket (Orthoptera: Stenopelmatidae)

Multiple mechanosensory organs form the subgenual organ complex in orthopteroid insects, located in the proximal tibia. In several Ensifera (Orthoptera), a small chordotonal organ, the so-called accessory organ, is the most posterior part of this sensory complex. In order to document the presence of this accessory organ among the Ensifera, the chordotonal sensilla and their innervation in the posterior tibia of two species of Jerusalem crickets (Stenopelmatidae: Stenopelmatus) is described. The sensory structures were stained by axonal tracing. Scolopidial sensilla occur in the posterior subgenual organ and the accessory organ in all leg pairs. The accessory organ contains 10–17 scolopidial sensilla. Both groups of sensilla are commonly spatially separated. However, in few cases neuronal fibres occurred between both organs. The two sensillum groups are considered as separate organs by the general spatial separation and innervation by different nerve branches. A functional role for mechanoreception is considered: since the accessory organ is located closely under the cuticle, sensilla may be suited to detect vibrations transferred over the leg's surface. This study extends the known taxa with an accessory organ, which occurs in several taxa of Ensifera. Comparative neuroanatomy thus suggests that the accessory organ may be conserved at least in Tettigoniidea.     

Intraspecific karyotype variation is not concordant with allozyme variation in the Auckland tree weta of New Zealand, Hemideina thoracica (Orthoptera: Stenopelmatidae)

Nine karyotypes are described within a single species of common New Zealand tree weta. Their diploid numbers range from 11 to 25. The distribution of the karyotypes suggests that each had a single origin except the 17-karyotype which was the most common karyotype and had a disjunct distribution. The overall level of allozyme diversity observed is similar to that seen within many widespread taxa. The distribution of allozyme alleles did not coincide with the distribution of karyotypes within this species and the Neighbour-Joining tree was not concordant with the chromosome based sub-divisions of the species. Thus, no evidence was found to suggest that chromosomal differentiation has been acting as a barrier to the flow of alleles within H. thoracica. The lack of concordance of genetic markers is thought to result from rapid chromosome radiation and reticulate evolution. Northland peninsula of North Island, New Zealand is a region of high chromosomal and allozymic diversity in H. thoracica. This may have resulted from geographic isolation during the Pliocene when Northland formed an archipelago of many small low-lying islands.     

Localization of the circadian pacemakers of Hemideina thoracica (Orthoptera; Stenopelmatidae)

The location of the circadian pacemakers of the orthopteran Hemideina thoracica (White) has been investigated through observation of the effects of surgical removal of brain tissues (principally optic lobes and tracts) on free-running and entrained locomotor rhythms. Bilobectomy and severance of optic tracts invariably resulted in arrhythmicity, whereas rhythmicity was sustained following unilateral lobectomy, generally with increases in the free-running period (FRP) and decreases in both the active-phase lengths and activity-to-rest ratios of the rhythm. Bilobectomized subjects could be entrained by temperature cycles, but exhibited no transients or residual rhythmicity, indicating that temperature brought about a direct response or masking effect. These results support the hypothesis that the circadian locomotor pacemakers of Hemideina are located within each optic lobe, and that there are no extraoptic centers for the control of the timing of locomotor activity. Although confirmation of the pacemaker role of the optic lobes requires transplantation of the tissues, the conclusion may be drawn by inference from other studies (e.g., Leucophaea maderae--Page, 1983; Gryllus bimaculatus--Tomioka and Chiba, 1986). Light entrainment continued after surgical binding and blackening of the compound eyes and ocelli, supporting the view that direct illumination of neural tissue through the cuticle may be one possible pathway for light entrainment.     

Translocating a threatened New Zealand giant orthopteran, Deinacrida sp. (Stenopelmatidae): some lessons

Experiences from the first efforts to translocate an orthopteran, the Mahoenui giant weta (Deinacrida sp.), are described. Some of the problems included monitoring at low densities, transferred weta dispersing and coordinating the different components of the translocation programme over a long period of time. Options for translocation are discussed, such as using wild-caught or captive-bred animals. Techniques of release, such as immediate release or using an enclosure on the release site, allowing transferees to breed, then releasing their progeny, are also discussed. It was concluded that the latter was probably the most effective approach to translocation.     

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.     

条螽属和桑螽属雌性发声刺的比较观察

 报道了对尖翅条螽Ducetia attenuata Xia et Liu、日本条 螽D. japonica(Thunberg)、施氏条螽D. strelkovi Gorochov et Storozhenk o和中华桑螽K uwayamaea chinensis(Brunner)、长翅桑螽K. longipennis Shi et Zheng、札 幌桑螽K.sap porensis Mats.et Shir.的雌性发声刺的观察结果。这6个种的雌性发声刺在数量与 形态上具较明显的差异。