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 circadian locomotor rhythm of Hemideina thoracica (Orthoptera; Stenopelmatidae): the circadian clock as a population of interacting oscillators

ABSTRACT. The behaviour of the circadian locomotor rhythm of the New Zealand weta, Hemideina thoracica (White), supports the model that the underlying pacemaker consists of a population of weakly coupled oscillators. Certain patterns of locomotor activity, previously demonstrated almost exclusively in vertebrates, are presented here as evidence for the above hypothesis. They include after-effects of various pre-treatments, rhythm-splitting and spontaneous changes in the rhythm. After-effects, which describe the unstable behaviour of free-running circadian rhythms following particular experimental perturbations, have been observed in Hemideina following single light pulses, constant dim light, and laboratory and natural entrainment. Period changes occurred in the activity rhythm after single light pulses of 8-h and 12-h duration (25 lx). Constant dim light (0.1 lx) increased the free-running period (τ) of the activity rhythm, but the after-effect of constant dim light was either an increase or a decrease in τ. After-effects upon both τ and the active phase length of the activity rhythm were found following non-24-h light entrainment cycles with 8-h and 12-h light phases of 25 lx. Qualitative measurements of these after-effects upon τ are presented which reveal a relationship between both the direction and amount of change in τ, and the difference between entrainment cycle length (T) and pre-entrainment free-running period. The after-effect of natural entrainment was an initial short-period free-run (τ < 24h) lasting 5–10 days, generally followed by a rapid period lengthening to τ= 25–26 h. Support for the population model was provided by spontaneous dampening, recovery, and period changes of the rhythm, together with the disruption of the active phase following critical light perturbations, and rhythm-splitting. These Hemideina results are compared with the simulations of the Coupled Stochastic System of Enright (1980).     

A new species of tusked weta from the Raukumara Range,North Island,New Zealand (Orthoptera: Anostostomatidae: Motuweta)

Abstract

A new species of weta from mainland New Zealand is described and assigned to the previously monotypic genus Motuweta Johns and the genus redefined. Mandibles of adult males bear prominent horns. Motuweta riparia n. sp. is a moderate‐sized species (36 mm) found on the margins of first or second order streams in the eastern mid North Island ranges. Its escape reaction is to leap into the stream and remain underwater until danger has passed, a strategy which has probably enabled it to survive in predator‐infested areas.     

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.     

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.     

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     

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.     

Identification of a hybrid zone between distinctive colour variants of the alpine weta Hemideina maori (Orthoptera: Stenopelmatidae) on the Rock and Pillar range, southern New Zealand

The weta Hemideina maori occurs as yellow (to the north), black (to the south) and intermediate colour variants on the Rock and Pillar range in New Zealand. Isozyme electrophoresis revealed little genetic variation, whereas RFLP analysis of an amplified mtDNA sequence uncovered two haplotypes correlating completely with colour in allopatry and nearly so in sympatry. Intermediates had one or other haplotype. The observed distribution of colour variation and mtDNA genotypes is characteristic of a hybrid zone, perhaps formed by secondary contact. Work is continuing to locate nuclear DNA markers and to study the genetic interactions of the colour variants.     

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.     

Structure of the auditory system of the weta Hemideina crassidens (Blanchard, 1851) (Orthoptera,Ensifera, Gryllacridoidea,Stenopelmatidae)

Summary This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae.Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap.Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrounding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix.     

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.     

Phylogeographical pattern correlates with pliocene mountain building in the alpine scree weta (Orthoptera, anostostomatidae)

Most research on the biological effects of Pleistocene glaciation and refugia has been undertaken in the northern hemisphere and focuses on lowland taxa. Using single-strand conformation polymorphism (SSCP) analysis and sequencing of mitochondrial cytochrome oxidase I, we explored the intraspecific phylogeography of a flightless orthopteran (the alpine scree weta, Deinacrida connectens) that is adapted to the alpine zone of South Island, New Zealand. We found that several mountain ranges and regions had their own reciprocally monophyletic, deeply differentiated lineages. Corrected genetic distance among lineages was 8.4% (Kimura 2-parameter [K2P]) / 13% (GTR + I + Gamma), whereas within-lineage distances were only 2.8% (K2P) / 3.2% (GTR + I + Gamma). We propose a model to explain this phylogeographical structure, which links the radiation of D. connectens to Pliocene mountain building, and maintenance of this structure through the combined effects of mountain-top isolation during Pleistocene interglacials and ice barriers to dispersal during glacials.     

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.     

Cold tolerance of a New Zealand alpine cockroach, Celatoblatta quinquemaculata (Dictyoptera, Blattidae)

Abstract. Ecophysiological features, including survival and recovery from freezing and determination of the freezable water content, are reported for a cold-adapted cockroach Celatoblatta quinquemaculata Johns 1966 (Dictyoptera, Blattidae) inhabiting alpine communities at altitudes greater than 1300 m a.s.l. in mountains of Central Otago, New Zealand. Nymphs ranged from 15 to 51 mg live weight of which 67% was water. Cockroaches had a mean supercooling point temperature of ?5.4 ± 0.1°C; with recovery from freezing close to this temperature being rapid, but no recovery was observed when frozen at ?9 to ?10°C. The duration of exposure to freezing conditions and the time allowed for recovery (24–96 h) both influenced individual recovery and subsequent survival. Comparison of supercooling point data and survival shows that this species possesses a few degrees of freeze tolerance, and individuals have been found frozen in the field when subzero temperatures occur. Differential scanning calorimetry showed ≈ 74% of body water froze during cooling and between 24 and 27% of total body water was osmotically inactive (unfreezable under the experimental conditions). Carbohydrates, other than glucose at 7.5μg/mg fresh weight, were in low concentrations in the body fluids, suggesting little cryoprotection. No thermal hysteresis from antifreeze protein activity was detected in haemolymph samples using calorimetric techniques. It is suggested that slow environmental cooling rates, together with high individual supercooling points, confer a small amount of freezing tolerance on this species enabling it to survive low winter temperatures. This has allowed it to colonize and maintain populations in alpine habitats > 1300 m a.s.1. in New Zealand.     

Sexual selection and infection by ectoparasites in Wellington tree weta,Hemideina crassidens (Orthoptera: Anostostomatidae)

Abstract Sexual selection can affect the prevalence and intensity of infection of individuals by ectoparasitic mites. According to this theory, males should exhibit greater infection by parasites than females and juveniles should be less infected than adults. In the wild, I investigated whether prevalence and intensity of the chyzeriid mite, Nothotrombicula deinacridae (Dumbleton) differed between the sexes and between developmental stages in Wellington tree weta, Hemideina crassidens. Despite being under strong sexual selection, male tree weta did not exhibit greater parasitism and there was some evidence that adults and juveniles differed in prevalence. The sexual selection hypothesis was not supported in this study.     

Diversification of New Zealand weta (Orthoptera: Ensifera: Anostostomatidae) and their relationships in Australasia

New Zealand taxa from the Orthopteran family Anostostomatidae have been shown to consist of three broad groups, Hemiandrus (ground weta), Anisoura/Motuweta (tusked weta) and Hemideina-Deinacrida (tree-giant weta). The family is also present in Australia and New Caledonia, the nearest large land masses to New Zealand. All genera are endemic to their respective countries except Hemiandrus that occurs in New Zealand and Australia. We used nuclear and mitochondrial DNA sequence data to study within genera and among species-level genetic diversity within New Zealand and to examine phylogenetic relationships of taxa in Australasia. We found the Anostostomatidae to be monophyletic within Ensifera, and justifiably distinguished from the Stenopelmatidae among which they were formerly placed. However, the New Zealand Anostostomatidae are not monophyletic with respect to Australian and New Caledonian species in our analyses. Two of the New Zealand groups have closer allies in Australia and one in New Caledonia. We carried out maximum-likelihood and Bayesian analyses to reveal several well supported subgroupings. Our analysis included the most extensive sampling to date of Hemiandrus species and indicate that Australian and New Zealand Hemiandrus are not monophyletic. We used molecular dating approaches to test the plausibility of alternative biogeographic hypotheses for the origin of the New Zealand anostostomatid fauna and found support for divergence of the main clades at, or shortly after, Gondwanan break-up, and dispersal across the Tasman much more recently.     

History of weta (Orthoptera: Anostostomatidae) translocation in New Zealand: lessons learned, islands as sanctuaries and the future

Establishing new populations by transferring founder individuals from source populations has been effective for managing the recovery of many threatened species including some weta (Orthoptera: Anostostomatidae) in New Zealand. These large-bodied flightless insects are ‘flagship species’ for insect conservation in New Zealand and many are rare or threatened. The declining abundance of most weta species, particularly giant weta, can be attributed to the introduction of mammalian predators, habitat destruction, and habitat modification by introduced mammalian browsers. New populations of some weta have been established in locations, particularly on islands, where these threats have been eliminated or severely reduced in order to reduce the risk of extinction. Some populations were established to provide food for endemic vertebrates, ecosystem restoration and ready access for the general public. We illustrate how methods for both transferring weta and monitoring them have become more sophisticated by using a series of case studies. Other transfers of weta not included in the case studies are also summarised. We conclude by re-iterating the importance of documenting the transfer and post-release monitoring for all insect transfers, both for biogeographical reasons and to provide information to improve future transfers.     

Sexually dimorphic effect of mating on the melanotic encapsulation response in the harem‐defending Wellington tree weta,Hemideina crassidens (Orthoptera: Tettigonioidea: Anostostomatidae)

Reproductive activities are generally costly to immune responsiveness because limited resources required by reproduction are diverted away from immunity (and vice versa). Reproduction, however, is not expected to affect the immune response in males and females similarly as mating is expected to negatively affect male immunity more so than female immunity. Here, I test the phenotypic plasticity hypothesis in the Wellington tree weta (Hemideina crassidens), a sexually dimorphic orthopteran insect that is endemic to New Zealand. My laboratory experiment showed that although males had higher rates of melanotic encapsulation than females, contrary to prediction, females were the only sex significantly affected by mating and the effect was positive. In addition to immunity differing between the sexes, immune function can differ intrasexually, particularly when males are polymorphic and different investment strategies are used to maximize fitness. Male H. crassidens exhibit alternative mating strategies that are represented by three different morphotypes. I therefore explored whether the morphs differed in their melanotic encapsulation response and whether mating affected the morphs differently. I found no difference among morphs or an effect of mating on male immune response.     

An appraisal of simple tree-mounted shelters for non-lethal monitoring of weta (Orthoptera: Anostostomatidae and Rhaphidophoridae) in New Zealand nature reserves

When monitoring rare insect species, or when surveying faunas within nature reserves, it is desirable not to use indiscriminate lethal sampling techniques. In this investigation we assessed the usefulness of simple tree-mounted wooden shelters to monitor endemic weta (Orthoptera) in nature reserves in Canterbury, New Zealand. Fifty shelters were placed out at six sites and examined at three-monthly intervals for a year. A wide variety of invertebrates were found utilizing the shelters, with Arachnida, Blattodea and Collembola being the most common occupants. After three months over 80% of the shelters exhibited signs of use by invertebrates, increasing to 96% after 12 months. Only seven tree weta (Anostostomatidae) and one (dead) ground weta (Hemiandrus sp.) were observed in the shelters over the full 12 month period. There were 52 observations of cave weta (Rhaphidophoridae) in the shelters, 36 of which occurred at one site, Orton Bradley Park. Occupation of the shelters by cave weta was not affected by soil conditions, light intensity or aspect of the shelter. However, cave weta exhibited a preference for shelters less than 50 cm above the ground and for shelters attached to kanuka and vines. Although weta were found in only a small proportion (9%) of the shelters, this method proved useful in confirming the presence of weta without risk of harming vulnerable populations. These shelters are inexpensive and easy to manufacture and have potential for long-term non-lethal monitoring of weta and as a collection/carriage device for live specimens used in conservation translocations.