Assessment Notes

Justification

Thanks to the “Threatened Weta recovery plan”, the population sizes and distributions of this species' hosts, Giant Weta species, are increasing. On this basis the habitat and potential host population size of the four known hosts of C. kirkii have increased since 1996 and are further expanding. With only four fungarium specimens, however, the knowledge of its abundance and distribution within the range of its hosts is unknown, hence this species is assessed as Data Deficient.

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Taxonomic notes

This is a conspicuous endemic species of Cordyceps on threatened species of endemic giant weta - flightless insects.

The holotype of C. kirkii was collected in 1922, on the threatened Stephens Island Weta, Deinacrida rugosa (Categorised as globally VU (Vulnerable) in 1996 by IUCN), and the next specimens were from 1975 and 2014 - with a further recent photograph (no specimen) from 2018.

Sequence data from the 2014 specimen of C. kirkii for nSSU, nLSU, TEF, RPB1, and RPB2 was incorporated into the Sanjuan et al. (2014) phylogenetic paper on orthopteran Cordyceps of Columbia. C. kirkii is confirmed as a true Cordyceps, but phylogenetically distinct from the Colombian orthoptera-associated species. No genetic data is known for other New Zealand species of Cordyceps.

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Geographic range

This species is known to date from only three in-shore islands where rats have been eradicated, and one location on the mainland - Westland, South Island. The islands, such as 150 ha Stephens Island, are small.

Although the obligate host of the holotype specimen, Deinacrida rugosa, is present on five small islands and two islets, Cordyceps kirkii has been recorded from only two of these, but it may not have been searched for at these other locations. To date, it has mostly been found by entomologists looking at Weta, rather than mycologists seeking the fungus.

The record from northern Hauturu/Little Barrier Island, where its presence is based on convincing photographic evidence only (without a voucher specimen) is not included on the map.

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Population and Trends

The population size and trend are unknown. The host is confined to five rodent-free islands and two islets in New Zealand, plus recent translocations. Arguably the Cordyceps could be more threatened than the threatened hosts.

Population Trend: unknown

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Habitat and Ecology

This fungus is parasitic on species of Weta. On the basis of known specimens, the species is apparently confined to Giant Weta, though recorded from four Weta species: Deinacrida rugosa (Stephens Island Giant Weta; Cook Strait Weta), D. heteracantha (Wētāpunga), and Hemiandrus maculifrons. It is presumably parasitic, sporulating on dead Weta. Most Giant Weta are now confined to New Zealand off-shore islands where rats have been eradicated, or on mainland locations with predator control.

D. rugosa, the host of the holotype specimen, prefers dense grassland and low growing shrubs in open situations. On Mana Island, it now occurs in rank grass and shrubland including tauhinu (Cassinia leptophylla). Predators include reptiles and birds, and most significantly rats (unless eradicated) (from http://www.doc.govt.nz/Documents/science-and-technical/tsrp25.pdf).

Cordyceps kirkii, previously recorded in New Zealand on the Stephens Island / Cook Strait Giant Weta (Deinacrida rugosa) and the Ground Weta (Hemiandrus maculifrons), has been newly recorded on Hauturu (Little Barrier Island) on dead Wetapunga, (Deinacrida heteracantha) [Photos Lyn Wade/David Stone/unknown]. While parasitic, this native Cordyceps is unlikely to negatively affect Wetapunga at a population level.

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Threats

The main threat is survival of its host. The decline of most Wētā is due to three major causes:
- Predation: Wētā have evolved alongside native predators such as birds, reptiles, and bats. The introduction of predators such as rats, mustelids, cats, and hedgehogs has resulted in a sharp increase in the rate of predation.
- Habitat destruction: Caused by human impacts
- Browsers: Modification of Wētā habitat caused by introduced browsers.


For example, Deinacrida rugosa is confined to certain offshore, rodent free nature reserve islands. Exotic predator-free status needs to be maintained indefinitely in these habitats. Translocations of Wētā to other reserve islands and recently to a mainland predator-free reserve has been successful. A population explosion of the native and also threatened reptile Tuatara, that eats Weta, could also potentially diminish the Wētā population at a local level.

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Conservation Actions

No conservation actions have been undertaken specifically for Cordyceps kirkii.

However, there has been active conservation effort to support survival of several species of giant Weta. For example, the host Deinacrida rugosa, is secure on Stephens Island (Takapourewa Nature Reserve) where two of our four specimens of C. kirkii were collected.  This island holds the world’s largest population of Tuatara, that naturally prey on Weta and other invertebrates. Other species found there include Fairy Prion, seven species of lizard and the endemic Hamilton’s Frog (though latter too small to consume Weta).

Conservation initiatives to support the Stephens Island / Cook Strait Giant Weta (from Sherley (1998) http://www.doc.govt.nz/Documents/science-and-technical/tsrp25.pdf):

“Cook Strait giant weta (Deinacrida rugosa) 

• A self-sustaining and expanding population has been established by translocating weta from Mana Island to Maud Island. Transfer of weta from Mana Island to Somes Island was initiated in 1996. 
• Captive breeding techniques have been developed. 
• Field research on dispersal behaviour and habitat use has been completed. Mice (presumed to prey on weta) have been removed from Mana Island which is considered to be the species stronghold”

“Distribution and abundance: Deinacrida rugosa is found on five rodent-free islands and two islets in the Cook Strait vicinity; North, South and Middle Trio Islands, Stephens Island, Maud Island, Matiu/Somes Island, and Mana Island. This weta is abundant on Mana Island, and healthy populations are also present Stephens and Middle Trio Island. The population on Maud Island was introduced in 1976, and is increasing (Meads and Notman 1992a). D. rugosa was introduced to Matiu/Somes Island in 1996.”

Similar data and conservation actions have been undertaken for other Giant Weta species, and these actions collectively are likely having spin-off benefits to secure the long-term survival of C. kirkii.

Research is needed on several aspects of this species, beginning with a basic understanding of the biology of the species, and its interaction with its host - including whether the relationship is parasitic, commensal, or mutualistic. In addition, search effort is needed on other island habitats of the host to evaluate the distribution of Cordyceps and evaluate the population size of C. kirkii. Further, the phylogenetic relationships of New Zealand Cordyceps need examing in a global context. It would also be valuable to establish whether C. kirkii shows any variation morphologically or genetically in relation to its different host Weta species.

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Use and Trade

Giant Weta, the hosts of this species, are sought after (dead or alive) by some collectors, but government control is reasonably tight via application of conservation permits for collection - with prosecutions likely for unpermitted holders of Weta.

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Source and Citation

Buchanan, P. 2019. Cordyceps kirkii. The IUCN Red List of Threatened Species 2019: e.T58517597A58517712. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T58517597A58517712.en .Accessed on 3 February 2024

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• Country occurrence