Hemiandrus pallitarsis

Hemiandrus pallitarsis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Orthoptera
Family: Anostostomatidae
Genus: Hemiandrus
Species: H. pallitarsis
Binomial name
Hemiandrus pallitarsis
Walker, 1869
Male Hemiandrus pallitarsus

Hemiandrus pallitarsis are a species of ground weta endemic to New Zealand. Being a ground weta, they are often found in burrows in the ground during the daytime (as they are also nocturnal). They are abundant within their distribution and are classified as "non-threatened", however they are an important food source for kiwi, in areas where kiwi are present. This species can be identified by a single foretibial spine, three prolateral spines, and four retrolateral spines on the mesotibia, and their tibia lacks a tympanal membrane (they hear only through vibrations in the ground, which is adaptive for their burrowing lifestyle). The female has an unusual appendage on her abdomen, and the male has blackened hooks on his last tergite. Whilst this species has a two year life cycle, their diet is largely unknown. The diet of other species in this genus however varies from omnivorous, to carnivorous, to herbivorous. This species of weta is unusual for an insect in that the female looks after her eggs and nymphs, this is known as maternal care.

Taxonomy

Hemiandrus pallitarsis was first described by Francis Walker in 1871, but was placed in the genus Libanasa.[1] In 1906 W. F. Kirby placed this species in the Ceuthophilus genus. Later on, in 1938, Kjell Ander described the Hemiandrus genus, and gave this species the species name of furcifer[2]. This species is therefore synonymous with Libanasa pallitarsis[1], but also with Hemiandrus furcifer (Ander, 1938).[3][2]

Habitat/Distribution

Hemiandrus pallitarsis are endemic to the North Island of New Zealand. They are widespread throughout this distribution[4][5] and are relatively abundant.[6] Because they are a ground weta, they are often found in burrows in the ground during the day,[7] as they are a nocturnal species.[8] During the night however, they are quite active on the ground, but are also found in vegetation such as beech trees,[9] kanuka bushes[10] and on leaves of plants such as kawakawa.[5] H. pallitarsis are often found at elevations below 200 metres.[10]

Conservation

The New Zealand Department of Conservation classified this species as "not threatened" in 2014.[11] These weta are widespread throughout their distribution,[4][5] and are relatively abundant,[6] therefore they are a species of least concern. Because they are nocturnal however, they are an important, and accessible food source for kiwi, in distributions where kiwi are present.[12]

Diet

No published article has described the diet of this species. The diet of other Hemiandrus species varies from carnivorous,[13] to omnivorous (fruit, invertebrates, and seeds),[14] to herbivorous (apricots and grasses),[15] therefore it is hard to know which diet this species specialises in.

Morphology

Hemiandrus pallitarsis are morphologically identified by having: a single foretibial spine, three prolateral spines, and four retrolateral spines on the mesotibia.[8] Adult females of this species have an elbow-like, forked appendage on their abdomen, formed from one of her sternites; this is the only species in this genus to have such an enlarged appendage.[16] Other species of this genus have similar appendages, however nowhere near as large as in the pallitarsis.[16] These females are also distinguished from other species in that they have a short ovipositor,[17][3] so short that it is often mistaken for not being there entirely,[14] and therefore these females are often mistakenly identified as males. The Hemiandrus genus is unusual in that some of the species have a long ovipositor, while other species have a short ovipositor.[5] The different length of this organ can aid in the differentiation between species.[5] The males of this species can be identified by blackened hooks on the last tergite.[10] These weta also have no tympanum, and instead are able to detect sound through their cuticle, which is adaptive for their underground lifestyle.[4] This means that their tibia lack the tympanal membranes or vestiges of other Orthoptera legs (this can only be seen with the use of a microscope).[4]

Breeding

Hemiandrus pallitarsus female

Hemiandrus pallitarsis come out of their burrows at night and adults will often sit on top of leaves (such as kawakawa) and use pheromones and drumming to attract mates, it is on top of these leaves that most matings take place.[5] This drumming sound is produced by the drumming of the abdomen on a substrate, such as a plant leaf.[8] The special appendage on the female's abdomen is thought to function in acquiring nuptial gifts from the male,[16] these gifts contain nutrients and the more nutrients a female acquires from a male, the more eggs she can lay.[16] There is a positive correlation between appendage size and nuptial gift size, and therefore between appendage size and the number of eggs laid by a female.[16] This suggest that this structure is sexually selected upon by males, as the larger the appendage, the larger the female's fitness.[16] The females will burrow to create brood chambers under the ground (2.5 centimeters deep at most[5]) to lay their eggs in, staying with the eggs until they hatch (most of the time until they die).[18] They lay about 50 eggs at a time, the short ovipositor of this species aids in the laying of eggs within the underground brood chamber, rather than into the soil as in other Hemiandrus species.[14] Maternal care is rare in Orthopterans, however is exhibited by this species.[18] There is continual care of the clutch (by covering them in soil and even moving the eggs when the burrow floods) but there is also physical, aggressive defense of the clutch.[5] Other species within this genus exhibit maternal care too, but only the species which have short ovipositors.[5] They lay their eggs in July,[15] and hatching occurs in September and October[5] (these are winter and spring months in New Zealand). Immature individuals are trapped most often between the months of December and March[19] and adults are found throughout the year.[17] Juveniles most likely take up to a year to develop into an adult.[17] They then live for approximately two years.[16]

References

  1. 1 2 Walker, F.; Gray, J. E. (1869). Catalogue of the specimens of Dermaptera Saltatoria and supplement of the Blattari in the collection of the British Museum. London, England.: British Museum (Natural History), Department of Zoology. p. 24.
  2. 1 2 Johns, P. M. (1997). "The Gondwanaland weta: family Anostostomatidae (formerly in Stenopelmatidae, Henicidae or Mimnermidae): nomenclatural problems, world checklist, new genera and species". Journal of Orthoptera Research. 6: 125–138. JSTOR 3503546.
  3. 1 2 Johns, P. M. (2001). Distribution and conservation status of ground weta, Hemiandrus species (Orthoptera: Anastostomatidae) (PDF). Wellington, New Zealand: Department of Conservation. Retrieved 7 June 2018.
  4. 1 2 3 4 Strauß, J.; Lomas, K; Field, L. H. (2017). "The complex tibial organ of the New Zealand ground weta: sensory adaptations for vibrational signal detection". Scientific Reports. 7 (1). doi:10.1038/s41598-017-02132-1.
  5. 1 2 3 4 5 6 7 8 9 10 Gwynne, D. T. (2004). "Reproductive Behavior of Ground Weta (Orthoptera: Anostostomatidae): Drumming Behavior, Nuptial Feeding, Post-copulatory Guarding and Maternal Care". Journal of the Kansas Entomological Society. 77 (4): 414–428. doi:10.2317/E-34.1.
  6. 1 2 Chappell, E. M.; Webb, D. S.; Tonkin, J. D. (2014). "Notes on sexual size dimorphism, sex ratio and movements of adult ground weta (Walker) (Orthoptera: Anostostomatidae)". New Zealand Entomologist. 37 (2): 83–92. doi:10.1080/00779962.2013.856377.
  7. ↑ Gwynne, D. T. (2014). "A secondary copulatory structure in a female insect: a clasp for a nuptial meal?". Naturwissenschaften. 89 (3): 125–127. doi:10.1007/s00114-002-0298-y.
  8. 1 2 3 Chappell, E. M.; Trewick, S. A.; Morgan-Richards, M. (2012). "Shape and sound reveal genetic cohesion not speciation in the New Zealand orthopteran, Hemiandrus pallitarsis, despite high mitochondrial DNA divergence". Biological Journal of the Linnean Society. 105 (1): 169–186. doi:10.1111/j.1095-8312.2011.01777.x.
  9. ↑ Brockie, Robert (1992). A living New Zealand Forest. Hong Kong: Bateman. ISBN 1 86953 039 X.
  10. 1 2 3 Chappell, E. M.; Webb, D. S.; Brown, A. J.; Tonkin, J. D. (2014). "A preliminary survey of altitudinal variation in two ground wētā species, (Walker) and (Walker) (Orthoptera: Anostostomatidae)". New Zealand Entomologist. 38 (1): 1–6. doi:10.1080/00779962.2014.922234.
  11. ↑ Trewick, S.; Morris, S. J.; Johns, P.; Hitchmough, R.; Stringer, I. (2012). The conservation status of New Zealand Orthoptera.
  12. ↑ "Distribution and conservation status of ground weta, Hemiandrus species (Orthoptera Anostostomatidae)" (PDF). Department of Conservation. p. 15. Retrieved 8 April 2012.
  13. ↑ Cary, P. R. L. (1983). "Diet of the ground weta (Orthoptera: Stenopelmatidae)". New Zealand Journal of Zoology. 10 (3): 295–297.
  14. 1 2 3 Tayolor Smith, B. L.; Morgan-Richards, M.; Trewick, S. A. (2013). "New Zealand ground wētā (Anostostomatidae: ): descriptions of two species with notes on their biology". New Zealand Journal of Zoology. 40 (4): 314–329. doi:10.1080/03014223.2013.804422.
  15. 1 2 Basri, W. M. (1978). The biology and economic impact of the weta, Hemiandrus sp. (Orthoptera : Stenopelmatidae) in an apricot orchard, Horotane Valley (Thesis). Lincoln College, University of Canterbury.
  16. 1 2 3 4 5 6 7 Gwynne, D. T. (2005). "The secondary copulatory organ in female ground weta (Hemiandrus pallitarsis, Orthoptera: Anostostomatidae): a sexually selected device in females?". Biological Journal of the Linnean Society. 85 (4): 463–469. doi:10.1111/j.1095-8312.2005.00510.x.
  17. 1 2 3 Stringer, I. A. N. (2006). Distinguishing Mercury Island tusked weta, Motuweta isolata, from a ground weta, Hemiandrus pallitarsis (Orthoptera: Anastostomatidae) in the field, with observations of their activity (PDF). Wellington, New Zealand: Department of Conservation. Retrieved 15 June 2018.
  18. 1 2 Gwynne, D. T. (1995). "Phylogeny of the Ensifera (Orthoptera): A Hypothesis Supporting Multiple Origins of Acoustical Signalling, Complex Spermatophores and Maternal Care in Crickets, Katydids, and Weta". Journal of Orthoptera Research (4): 203. JSTOR 3503478.
  19. ↑ Barratt, B. I. P.; Patrick, B. H. (1987). "Insects of snow tussock grassland on the East Otago Plateau". New Zealand Entomologist. 10 (1): 69–98. doi:10.1080/00779962.1987.9722513.
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