''Sigaus robustus'' is a New Zealand species of grasshopper classified as Threatened: Nationally Endangered. It is restricted to open stony habitat of the

Mackenzie Basin The Mackenzie Basin (), popularly and traditionally known as the Mackenzie Country, is an elliptical intermontane basin located in the Mackenzie and Waitaki Districts, near the centre of the South Island of New Zealand. It is the largest su ...

of the

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasma ...

. Although a grasshopper, it is a poor jumper, relying on camouflage to hide from predators. It is threatened by introduced mammals such as stoats,

hedgehogs A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction ...

, and rats. The New Zealand

entomologist Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

Tara Murray told '' North & South'' magazine in 2019: “They can actually jump, they just don’t land very well. On a hot day, an adult male can jump up to 1.5m, multiple times. Females are bulkier, so they don’t jump as far. These grasshoppers freeze as a first defence. If they do jump, it often ends as a back flop, belly flop or general ‘thock’ on the ground.”

Species description

''Sigaus robustus'' is extremely well camouflaged, often relying on visual

crypsis In ecology, crypsis is the ability of an animal or a plant to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and ...

as passive defense against predation. It is also sexually dimorphic; adult males have a body length of 18–22 mm (0.71–0.87 in.) and adult females 38–42 mm (1.5–1.7 in.).White, E. G. 1994. Ecological research and monitoring of the protected grasshopper ''Brachaspis robustus'' in the Mackenzie Basin. Pages 1-50. Department of Conservation, Wellington, New Zealand. Males are estimated to have 5 instars and females 6, the same as several other sub-alpine and alpine grasshopper species within New Zealand. The wings on ''S. robustus'' are very small, between , making this species flightless like most of New Zealand grasshoppers. There are three known colour morphs for adult ''S. robustus'': 'Grey', 'Orange' and 'Black'. The most common colour morph is 'Grey' at approximately 60% of adult ''B. robustus''; 'Orange' is about 40%, and the very rare 'Black' is less than 0.5%. File:NZAcrididae7.JPG, Colour morph 'Grey'. File:NZAcrididae5.JPG, Colour morph 'Orange'. File:NZAcrididae6.jpg, Colour morph 'Black'. Robust grasshopper nymph on rocks

Distribution

''Sigaus robustus'' is only known from the Tekapo, Pukaki and Ohau river catchments in the

. It can be found as far south as

Lake Benmore Lake Benmore is New Zealand's largest artificial lake. Located in the South Island of New Zealand and part of the Waitaki River, it was created in the 1960s by construction of Benmore Dam. Characteristics The lake has an area of about 75&nbs ...

(44°20′29″S 170°12′42″E) and as far north as the upper Fork Stream (43°58′24″S 170°24′04″E). ''B. robustus'' prefers open habitat of riverbeds and river terraces. Most of this stony habitat has been modified by introduced plant species and hydro-electric dams. The elevation range of ''Sigaus robustus'' is between 352 m (1,155 ft) on the lower Ohau River and 1,060 m (3,480 ft) the upper Fork Stream. Detailed searches since 1980 have been carried out throughout the Mackenzie Basin and a good understanding of its current distribution is now known.Morris, S.J. 2005. The resurvey of the old historic ''Brachaspis robustus'' sites in the Mackenzie Basin. Department of Conservation, Twizel, New Zealand.

Life history

The lifespan of ''S. robustus'' is more than two years. Eggs are laid from early summer to mid autumn. Adult females lay one or two egg batches a season, each containing between 17–35 eggs. The majority of nymph emergence occurs in mid-summer, but early instar ''S. robustus'' have been seen later in the season. Because of the timing of emergence, it is thought eggs require a winter period in order to develop fully. This not an uncommon requirement for New Zealand grasshoppers. The nymphs then overwinter, often surviving temperatures well below 0 °C, and reach adulthood the following summer. Adult males will copulate with multiple females and vice versa, suggesting this species has a promiscuous mating system. The ratio of male to female ''B. robustus'' alters over New Zealand summer: at the start of the summer in November the ratio is 56% male and 44% female. By December females (57%) outnumber males (43%). For the rest of summer, males predominate: in January at 54% male to 46% female, and in March 82% male and only 18% female.

Habitat and diet

''Sigaus robustus'' is always found in very rocky areas (stony floodplain terraces, fluvio-glacial outwash, recent fluvial outwash, and rocky braided river), and is never found in vegetation. It is a generalist herbivore and is known to eat '' Anthosachne scabra'' (syn. ''Elymus rectisetus'') and ''

Poa pratensis ''Poa pratensis'', commonly known as Kentucky bluegrass (or blue grass), smooth meadow-grass, or common meadow-grass, is a perennial species of grass native to practically all of Europe, North Asia and the mountains of Algeria and Morocco. Altho ...

'', the herb '' Achillea millifolium'', and unidentified

mosses Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) ''sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and h ...

and

lichens A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Faeces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

analysed during spring suggested that moss and lichen are important in its diet; this might reflect their ability to absorb moisture at night. Food succulence is important in grasshopper diets, and mosses and lichens may provide a means of withstanding the aridity and drought of the Mackenzie Basin.

Conservation

Two species of grasshopper are listed for protection under the

Wildlife Act 1953 Wildlife Act 1953 is an Act of Parliament in New Zealand. Under the act, the majority of native New Zealand vertebrate species are protected by law, and may not be hunted, killed, eaten or possessed. Violations may be punished with fines of up to ...

of New Zealand: ''B. robustus'' and '' Sigaus childi''. '' Sigaus takahe'' is also indirectly protected as it is only known from the Murchison Mountains Specially Protected ( Takahē) Area. As early as the 1960s, ''S. robustus'' was noted as rare and in need of conservation action. In 1993, it was estimated that there were only approximately 800 adults in the wild. By the end of 2009/2010 summer it was estimated that this had declined to approximately 600 adults. In 1993, most adults were found in three key very large populations and only a few sub-populations; by 2010, numerous new sub-populations have been discovered, but the three key populations from 1993 were now very sparse and made up of numerous sub-populations. Introduced mammalian predators are one of the known threats to ''B. robustus''. NZAcrididae4

Both introduce mammalian predators and native lizards are likely to pose a substantial threat to ''S. robustus''. In December 2017, 20 ''B. robustus'' were fitted with radio transmitters which operated for 3–12 days to determine their home range for future translocations. In July 2018 a 440 ha area in the Mackenzie Basin known as the "Tekapo Triangle" was transferred to the control of the Department of Conservation and set aside as a reserve for ''S. robustus''. Six pairs were taken into captivity in an attempt to breed them.

Type information

*Bigelow, R.S. 1967. ''The Grasshoppers of New Zealand, Their Taxonomy and Distribution''. University of Canterbury, Christchurch. *Type locality: Ahuriri River,

Otago Otago (, ; mi, Ōtākou ) is a region of New Zealand located in the southern half of the South Island administered by the Otago Regional Council. It has an area of approximately , making it the country's second largest local government reg ...

. . It is virtually certain that ''B. robustus'' is now absent from the holotype and paratype localities.White, E.G. 1994: Ecological research and monitoring of the protected grasshopper ''Brachaspis robustus'' in the Mackenzie Basin. Dept. of Conservation, Wellington, N.Z.Morris, S.J. 2010: Monitoring ''Brachaspis robustus'' ~ 2009/2010 Summer. Department of Conservation, Twizel. These localities and surrounding suitable habitat for ''B. robustus'' have been searched several times unsuccessfully. *Type specimen: Female; 21 April 1963; R.R. Granger;

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

and

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

are deposited in the Canterbury Museum,

Christchurch Christchurch ( ; mi, Ōtautahi) is the largest city in the South Island of New Zealand and the seat of the Canterbury Region. Christchurch lies on the South Island's east coast, just north of Banks Peninsula on Pegasus Bay. The Avon Rive ...

References

External links

* ''Brachaspis robustus'' on

RNZ Radio New Zealand ( mi, Te Reo Irirangi o Aotearoa), commonly known as Radio NZ or simply RNZ, is a New Zealand public-service radio broadcaster and Crown entity that was established under the Radio New Zealand Act 1995. It operates news and cu ...

Critter of the Week ''Critter of the Week'' is a weekly RNZ National programme about endangered and neglected native plants and animals of New Zealand. Beginning in 2015, ''Critter of the Week'' is an approximately 15-minute discussion between Nicola Toki of the ...

''
27 November 2015
{{Taxonbar, from=Q4953266 Catantopinae Acrididae of New Zealand Endemic fauna of New Zealand Endemic insects of New Zealand Insects described in 1967