Introduction
editThe Deinacrida heteracantha belong to the Order Orthoptera and Family Anostostomatidae, known as the Weta [1]. In particular D. heteracantha is part of the Northern Arboreal Giant Weta lineage; they are also known as the Wetapunga [2][3]. This lineage is a monophyletic group in both morphological and genetic analysis wise [2]. The Maori, the indigenous people of New Zealand, call this species Wetapunga [4]. Wetapunga, in Maori, means ugliness [4]. This lineage of crickets is one of largest in the world and are found in New Zealand and more specifically on Little Barrier Island [1][2]. This species of cricket is activate both in the day and night and can be found above ground on the vegetation during the day; this when mating occurs. [2][5]. D. heteracantha are nocturnal when it comes to their main activites such as feeding [5].
Identification
editD. heteracantha, alone, can weigh up to 70g, but on average weigh between 9-35g, and are approximately 75mm in length [1][2][3]. D. heteracantha are a sexually dimorphic species, with the females being much larger than the males [2]. These large crickets have a broad body and a round head, along with short mandibles [2]. Compared to other cricket species the Wetas have a relatively short antennae, but can deliver a strong kick with their hind legs [1]. They are generally wingless as well [1]. They are mainly herbivorous and feed on foliage in the forest they inhabit [2].
Habitat
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D. heteracantha are arboreal forest insect dwellers found on Little Barrier Island which lies off the coast of New Zealand. This island is only 3083ha in size [2]. 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 [2]. The second-growth forest is dominated by Silverfern, Nikau palm, Mahoe, and Kohekohe [3]
Behaviour
editAs adults these giant crickets live a nomadic lifestyle [2] This type of lifestyle means that these crickets do not live in the same place, but move to a new location periodically [6]. They live a solitary lifestyle and most of their activity is done at night (ie. Feeding and moving) [3]. They can be found above ground level under loose bark or in the cavities of Mahoe and Pohutukawa trees [2]. During the day and night males tend to move farther than the females. The male would follow the female by staying back about 25cm from her; this is observed during the night time [3].
Life Cycle and Reproduction
editThe life cycle of D. heteracantha are 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 15cm2 and about 2-3cm deep. Females only produce an indefinite amount of eggs. Females lay eggs for the rest of their lives, but only a limited number of them are fertilized during each copulation. The eggs incubate on average for 125 days and only 36% of the eggs survive to hatch [5].
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 to 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 [5].
D. heteracantha show no courtship rituals. No stridulatory signals have been observed; sex recognition is done by contact only [5].
How They Produce Sound
editD. heteracantha possess a stridulatory apparatus. This apparatus is the sound producing organ based on the mechanism of rubbing one body part against another body part [7]. There is a great variety in these structures seen in Orthoptera. Certain behaviours are associated with the sounds being produced by the Orthoptera [8] . 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 [9].
Threats
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In the 1950’s stridulatory were commonly seen in abundance on Little Barrier Island. However, years down the road their population showed a noticeable decrease in their numbers. It is not habitat destruction that caused their population to decline, instead it was due to predation [10]. Feral cats once roamed the island until they were completely eradicated in the 1980s [2]. These cats might have fed on the juveniles of D. heteracantha as they are more vulnerable [5].
Kiore (Rattus exulans), a rat, are one of the top predators of D. heteracantha. These rats mostly prey on the juveniles of these crickets. Kiore prey on the crickets during the night. An increase of the Kiore population occurred after the feral cats were eradicated. Saddlebacks, a bird, prey on the crickets during the day. With predators present in both the daytime and the night time, it becomes difficult for D. heteracantha to keep up their population numbers [10]. There is evidence suggesting that these rats have a negative impact on the population of these crickets. It has been shown that this invasive rodent, and other invasive rodents and vertebrates, have driven invertebrate populations to extinction [11]. The removal of the Kiore in 2004 was a success. The population size grew back each year and a four-fold increase after the first six years since the removal [12].
Other predators include Tuataras, Geckos, Kingfishers, Long-tailed cuckoo, and the North Island Brown Kiwi. At night the lizards and tuataras will prey on D. heteracantha. During the summer the long-tailed cuckoo is present on Little barrier Island and the Kiwi’s are found on the island year round. Kingfishers are found in the same tree as D. heteracantha, making them an easy target for these birds [5].
- ^ a b c d e Nasrecki, P. 2013. Grasshoppers and their relatives. Elsevier Inc. 3: 247-264.
- ^ a b c d e f g h i j k l m Field, L.H. 2001. The Biology of Wetas, King Crickets and their Allies. New York: CABI Publishing.
- ^ a b c d e f Watts, C. and Thornburrow, D. 2011. Habitat use, behavior and movement patterns of a threatened New Zealand giant weta, Deinacrida heteracantha (Anostostomatidae: Orthoptera). Journal of Orthoptera Research 20(1): 127-135
- ^ a b Maori.com. 2015. Maori. Accessed November 20, 2015 from Link text
- ^ 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
- ^ Encyclopedia Britannica. 2015. Nomadism. Accessed November 20, 2015 from Link text
- ^ Cite error: The named reference
Nasrecki2013was invoked but never defined (see the help page). - ^ 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.
- ^ 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.
- ^ 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.
- ^ St. Clair, J.J.H. 2011. The impacts of invasive rodents on island invertebrates. Biological Conservation (144): 68-81.
- ^ 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.