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Deinacrida heteracantha

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Deinacrida heteracantha
Holotype specimen (female)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Orthoptera
Suborder: Ensifera
Family: Anostostomatidae
Genus: Deinacrida
Species:
D. heteracantha
Binomial name
Deinacrida heteracantha
White, 1842
Synonyms

Deinacrida heteracantha, also known as the Little Barrier giant wētā or wētāpunga (Māori: wētāpunga),[2] is a wētā in the order Orthoptera and family Anostostomatidae. It is endemic to New Zealand, where it survived only on Hauturu (Little Barrier Island).[3] This very large flightless wētā mainly feeds at night, when it can be found above ground in vegetation. It has been classified as vulnerable by the IUCN due to ongoing population declines and restricted distribution. Its NZTCS threat classification was changed to "Threatened - Nationally increasing" in 2022 because it has been successfully translocated to 7 predator-free islands.[4][5]

Taxonomy

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Deinacrida heteracantha was first described by Scottish zoologist Adam White in 1842.[6] William Colenso described the species as Hemideina gigantea in 1882;[7] a name which was later brought into synonymy with D. heteracantha.[8] The holotype that Colenso used, collected in 1839, is the oldest known entomological specimen of a New Zealand species located in New Zealand.[8]

Description

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Wētāpunga is the largest of the Deinacrida species.[9][10] In captivity gravid Deinacrida heteracantha can weigh up to 70 g (2.5 oz),[10] but on average adult females weigh 32 g and adult males 7.4 g.[9] Average body length of adult females is around 65 mm (2.6 in) from head to tip of abdomen.[11][12][3] It is a sexually dimorphic species, with the females being much larger than the males. These large wētā have a broad body and a round head, along with short mandibles.[12] Compared to other cricket species wētā have relatively short antennae, but can deliver a strong kick with their hind legs. They are wingless.[11] The species is mainly herbivorous and feeds on forest foliage.[12]

White's original description of D. heteracantha is as follows:

Hind legs nearly twice the length of the insect; tibiae quadrangular, broadest behind, the edges armed with spines coming out alternately; spines very strong and sharp: body brown, beneath yellow: head punctured on the vertex; antennae at least 2 1⁄2 times the length of the insect: thorax punctured, with some small smoothish spaces in the middle; the lateral margins somewhat thickened: the head is not nearly so broad nor so large as in Anostostoma; the mandibles much shorter; the labial palpi have the terminal joint swollen at the end, when dry it is slightly compressed from shrinking; the maxillary palpi are very long; the three last joints cylindrical, the last longest, gradually clubbed at the end.[6]

Habitat

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Little Barrier Island

D. heteracantha are arboreal forest insect dwellers found on Little Barrier Island which lies off the coast of New Zealand. This island is only 3,083 hectares (7,620 acres) in size.[12] They once occupied forests in northern New Zealand including Northland and Auckland.[3] Their habitat range on Little Barrier Island is from second-growth forests located on the lower slopes of the island to the mid-level tall kauri forest.[12] The second-growth forest is dominated by silverfern, nīkau palm, mahoe, and kohekohe.[3]

Behaviour

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As adults these giant wētā live a nomadic lifestyle.[12] This type of lifestyle means that these wētā do not live in the same place, but move to a new location periodically.[13] They live a solitary lifestyle and most of their activity is done at night (i.e. feeding and moving).[3] They can be found above ground level under loose bark or in the cavities of mahoe and pōhutukawa trees.[12] During the day and night males tend to move farther than the females. The male would follow the female by staying back about 25 cm from her; this is observed during the night time.[3]

Life cycle and reproduction

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The life cycle of D. heteracantha is not tied to the seasons. They can live for up to two years. Eggs are laid in the summer months from October to December. The eggs will then hatch in March and April of the following year. D. heteracantha mate most months out of the year except for the winter months from June–August. Copulation will start in the morning and continue throughout the day. During copulation the spermatophore from the male is inserted into the female's subgenital plate. Females lay their eggs at night into moist soil. Each egg is laid singly or in groups of five in area that is about 15 cm2 and about 2–3 cm deep. Females produce an indefinite amount of eggs. Females lay eggs for the rest of their lives, but only a limited number of them are fertilised during each copulation. The eggs incubate on average for 125 days and only 36% of the eggs survive to hatch.[10]

After the eggs hatch there are ten instars that they go through until death. In females the ovipositor becomes visible at the third instar. At the sixth instar the difference between male and female sexes becomes obvious. Each instar lasts on average between five and six weeks. D. heteracantha has an extra instar compared to other species in its genus, this extra instar is what makes the nymphal period longer and their overall body size larger.[10]

D. heteracantha show no courtship rituals. No stridulatory signals have been observed; sex recognition is done by contact only.[10]

Sound generation

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D. heteracantha possesses a stridulatory apparatus. This apparatus is the sound producing organ based on the mechanism of rubbing one body part against another body part.[11] There is a great variety in these structures seen in Orthoptera. Certain behaviours are associated with the sounds being produced by the Orthoptera.[14] In the case of D. heteracantha there is a wide variation in the gross morphology of their stridulatory structures. Their stridulation plays a role in interspecific defense mechanisms. They use a femoro-abdominal mechanism to produce sound. This mechanism has two parts to it, a femoral peg and an abdominal ridge. The femoral pegs are an elongated and raised structure. There are two abdominal ridges present on D. heteracantha, a major and minor ridge. The major ridge is longer and higher than the minor ridge. The minor ridge does not normally come in contact with the femoral pegs. D. heteracantha has a wide-band linear magnitude spectra (kHz) that they produce for defensive sounds. They have a major peak at 20 kHz and a minor peak around 40–50 kHz. The shape of their stridulatory mechanism is why they can produce these frequency ranges.[15]

Threats

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Polynesian rat (kiore)

While D. heteracantha were commonly seen on Little Barrier Island in the 1950s, numbers have declined strongly since then. Predation rather than habitat destruction is regarded as the main cause for this.[16] Feral cats were present on the island until they were completely eradicated in the 1980s,[12] and may have fed on vulnerable juvenile D. heteracantha.[10]

Polynesian rats (Rattus exulans), or "kiore" in the Māori language, are one of the top predators of D. heteracantha, preying mostly on juveniles wētās which they kill during the night. An increase of the Polynesian rat population occurred after feral cats were eradicated. As saddlebacks prey on the wētā during the day, D. heteracantha are thus under constant predation pressure.[16] There is evidence suggesting that these rats have a negative impact on the population of these wētā, as is commonly the case with invasive rodents.[17] The removal of the kiore in 2004 was a success. The population size grew back each year and a four-fold increase was reported six years after the removal.[18]

Other predators include tuatara (Sphenodon punctatus), geckos, the North Island brown kiwi (Apteryx mantelli) during the night, and kingfishers and the long-tailed cuckoo (Urodynamis taitensis) by day.[10]

Captive breeding and release

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One of 150 D. heteracantha released on Tiritiri Matangi Island on 1 May 2014

D. heteracantha is currently classified as vulnerable by the IUCN.[1] Since 2008 the Department of Conservation has been involved in a captive breeding and release programme to mitigate the risk of having the entire population resident on one island. Individuals captured on Hauturu/Little Barrier Island have been successfully bred in captivity at Butterfly Creek and Auckland Zoo. The descendants have been released onto Motuora and Tiritiri Matangi Islands. Additionally adults from Hauturu/Little Barrier Island have been transferred directly to Motuora. It is hoped that the released D. heteracantha will eventually build up self-sustaining populations on these additional predator free islands. In 2016 an adult female was observed on Tiritiri Matangi Island in the area where the first population was released. She can only be a descendant of the initial translocated population of 25 individuals released in 2011.[19] Individuals translocated onto Tiritiri Matangi island in 2014 have been observed mating.[20] In 2018, 300 wētāpunga from Auckland Zoo were translocated to an island in the Noises; at that point 4300 captive-bred individuals had been released on islands in the Hauraki Gulf.[21] In 2023, over 300 juveniles were released onto two islands in the Bay of Islands.[22]

See also

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References

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  1. ^ a b World Conservation Monitoring Centre (1996). "Deinacrida heteracantha". IUCN Red List of Threatened Species. 1996: e.T6305A12602299. doi:10.2305/IUCN.UK.1996.RLTS.T6305A12602299.en. Retrieved 17 November 2021.
  2. ^ "Giant Wētā/Wētāpunga". New Zealand Department of Conservation. Retrieved 17 Jan 2019.
  3. ^ a b c d e f Thornburrow, Danny; Watts, Corinne (2011). "Habitat use, Behavior and Movement Patterns of a Threatened New Zealand Giant Weta, Deinacrida heteracantha (Anostostomatidae: Orthoptera)". Journal of Orthoptera Research. 20 (1): 127–136. doi:10.1665/034.020.0112. ISSN 1082-6467.
  4. ^ "NZTCS". nztcs.org.nz. Retrieved 2024-09-23.
  5. ^ Trewick, S. A.; Hegg; Morgan-Richards; Murray; Watts; Johns; Michel (2022). "Conservation status of Orthoptera (wētā, crickets and grasshoppers) in Aotearoa New Zealand" (PDF). New Zealand Threat Classification Series. 39 – via Department of Conservation, Wellington.
  6. ^ a b Early, John W. (2016). "Provenance of the type specimen of William Colenso's giant weta Hemideina gigantea". Records of the Auckland Museum. 51: 49–53. ISSN 1174-9202. JSTOR 90014742. Wikidata Q104815045.
  7. ^ Colenso, W. (1882). "Art. XL.—On some new and undescribed Species of New Zealand Insects, of the Orders Orthoptera and Coleoptera". Transactions and Proceedings of the New Zealand Institute. 14: 277–282. ISSN 1176-6158. Wikidata Q125475605.
  8. ^ a b White, Adam (1842). "Description of an orthopterous insect, and two new species of Crustacea, from New Zealand: in the collection of the British Museum". The zoological miscellany : to be continued occasionally. V: 78–79. Wikidata Q125475515.
  9. ^ a b McIntyre, M. (2001). The Ecology of some large weta species in New Zealand. Chapter 12 in [ed. L. H. Fields] The Biology of Wetas, King Crickets and their Allies. CABI Publishing. ISBN 0851994083.
  10. ^ a b c d e f g Richards, A.O. 1973. A comparative study of the biology of the giant wetas Deinacrida heteracantha and D. fallai (Orthoptera: Henicidae) from New Zealand. Journal of Zoology 169: 195-236
  11. ^ a b c Nasrecki, P. 2013. Grasshoppers and their relatives. Elsevier Inc. 3: 247-264.
  12. ^ a b c d e f g h Field, L.H. 2001. The Biology of Wetas, King Crickets and their Allies. New York: CABI Publishing.
  13. ^ Encyclopædia Britannica. 2015. Nomadism. Accessed November 20, 2015 from Link text
  14. ^ Field, L.H. 1993. Structure and evolution of stridulatory mechanisms in New Zealand Wetas (Orthoptera: Stenopelmatidae). International Journal of Insect Morphology and Embryology (22): 163-183.
  15. ^ Field, L.H. 1981. Stridulatory structures and acoustic spectra of seven species of New Zealand wetas (Orthoptera: Stenopelmatidae). International Journal of Insect Morphology and Embryology (11): 39-51.
  16. ^ a b Gibbs, G. and M., McIntyre. 1997. Abundance and future options for wetapunga on Little Barrier Island. Science for Conservation 48: 1-25. ISBN 0-478-018967.
  17. ^ St. Clair, J.J.H. 2011. The impacts of invasive rodents on island invertebrates. Biological Conservation (144): 68-81.
  18. ^ Green, C. J, G.W, Gibbs, and P.A, Barrett. (2011). Wetapunga (Deinacrida heteracantha) population changes following Pacific rat (Rattus exulans) eradication on Little barrier Island. IUCN, Gland, Switzerland: 305-308.
  19. ^ "Dawn Chorus - Bulletin 99" (PDF). Dawn Chorus: Bulletin. November 2014. ISSN 1171-8595. Archived from the original (PDF) on 29 January 2021. Retrieved 14 December 2015.
  20. ^ "Dawn Chorus - Bulletin 101". Dawn Chorus: Bulletin. May 2015. ISSN 1171-8595.
  21. ^ Saxton, Amanda (2018-09-07). "The island life for hundreds of giant wētāpunga". Stuff. Archived from the original on 2018-12-01. Retrieved 2021-08-31.
  22. ^ "'A real homecoming': Wētāpunga, predating dinosaurs, return to NZ islands". RNZ. 2023-08-21. Retrieved 2023-08-31.

Further reading

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