Lord Howe Island phasmid (Dryococelus australis) - critically endangered species listing

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Lord Howe Island Phasmid, Dryococelus australis (Montrouzier, 1855), is a large, flightless insect, “males reaching 120 mm (more commonly 106 mm) at adulthood and females 150 mm (more commonly 120 mm). Both sexes are uniformly black at maturity, often with a reddish-brown tinge. The body is generally smooth and shiny, and the intersegmental membranes between joints are pale grey. Adult males are distinguished by two conspicuous spines on the enlarged hind femur. Females have a long, pointed sheath (the operculum or subgenital plate) underneath the last segment, with a wider and more terminally tapering abdomen” (Honan 2008).

2. The Lord Howe Island Phasmid is currently known only from a single site located on Balls Pyramid, a rocky outcrop 23 km south east of Lord Howe Island in the Pacific Ocean (Priddel et al. 2003). The site is unusual on Balls Pyramid in being moist as a result of natural water drainage and where organic matter has accumulated over a “few square metres” (Priddel et al. 2003). The insects have been reported only from within a foraging area which is considered to be 30 m x 6 m where six Melaleuca howeana shrubs are located (Carlile et al. 2009). Melaleuca howeana is likely to be the only host plant for the Lord Howe Island Phasmid at this site.

3. The Lord Howe Island Phasmid has a very highly restricted geographic distribution, occupying a habitat that is precarious and probably sub-optimal (Carlile et al. 2009). The extent of occurrence (EEO) and area of occupancy (AOO) using the only records in the last 70 years are 4 km²; based on 2x2 km grid cells, the scale recommended for assessing area of occupancy by IUCN (2010). The potential habitat is severely fragmented with the population on Balls Pyramid isolated from its former habitat on Lord Howe Island.

4. The Lord Howe Island Phasmid was once very common on Lord Howe Island, to the extent that it was used as bait for fishing. The species became extinct there soon after the supply ship “S.S. Makambo” ran aground in 1918 and the Ship Rat, Rattus rattus came ashore with the cargo (Hindwood 1938, Hutton 1998) and spread rapidly throughout Lord Howe Island (Edgecombe 1987). As rat numbers increased, numbers of the Lord Howe Island Phasmid declined such that by 1935 the species was considered to be very rare, if not already extinct (Gurney 1947). The last phasmid was seen on Lord Howe Island in 1920 (Priddel et al. 2003). Later surveys of Lord Howe Island in 1954 and 1955 failed to detect the Lord Howe Island Phasmid (Paramonov 1963) and it was considered extinct until the discovery on Balls Pyramid of live individuals in 2001 (Priddel et al. 2003). The population on Lord Howe Island clearly underwent a massive reduction from being common in the early 1900s to extinct within a few decades.

5. There is uncertainty in estimates of abundance of the population on Balls Pyramid because surveys are constrained by the difficulties of accessing the site. In a 2001 survey two adults and one nymph were found as well as two eggs in a sieved sample of soil (Priddel et al. 2003). In 2002, a total of 24 live phasmids were observed (Priddel et al. 2003). The last survey of Balls Pyramid was in 2005 when 35 adults and five nymphs were recorded (Carlile et al. 2009). The current population size of the species is estimated to be extremely low with fewer than 50 mature individuals in the wild.

6. The very small and isolated population on Balls Pyramid may be threatened by a smothering vine. Priddel et al. (2003) observed that “Several Melaleuca howeana shrubs on the terrace occupied by D. australis were being invaded and smothered by the invasive vine Coastal Morning Glory (Ipomoea cairica). This vine can be particularly aggressive. It had penetrated several shrubs near the one occupied by the Lord Howe Island Phasmid, and if it spread further it could potentially damage the insect’s host plants, thereby threatening its continued survival.” Careful hand control treatments including scrape and paint and low pressure splatter gun applications of dense vines infestations away from any Melaleuca bushes (Lord Howe Island Board). The threat presented by the Ship Rat limits the capacity for expansion of the species’ geographic distribution to Lord Howe Island. Individuals from Balls Pyramid are highly unlikely to reach Lord Howe Island by natural means, but should they do so, any such founders would be subject to predation pressure from the Ship Rat. The species is also vulnerable to chance events due to its small population size and restricted distribution. ‘Predation by the Ship Rat Rattus rattus on Lord Howe Island’ and ‘Invasion and establishment of exotic vines and scramblers’ are listed as Key Threatened Processes under the Threatened Species Conservation Act, 1995.

7. In 2003, two pairs of phasmids were collected from Balls Pyramid and a captive breeding program initiated (Honan, 2008). There are now 800 adults in captivity which are producing viable eggs (D Priddel, pers. comm. July 2011). If plans to exterminate the Ship Rat on Lord Howe Island are realised, the captive breeding program should be able to supply good numbers of phasmids for field release. Phasmids are also available should the wild population on Balls Pyramid become extinct.

8. The Lord Howe Island Phasmid Dryococelus australis (Montrouzier, 1855) is listed as a Critically Endangered species in the Environment Protection and Biodiversity Conservation Act 1999.

9. The Lord Howe Island Phasmid Dryococelus australis (Montrouzier, 1855) is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:

Clause 7 Restricted geographic distribution and other conditions

The geographic distribution of the species is estimated or inferred to be:

and either:

Clause 8 Low numbers of mature individuals of species and other conditions

The estimated total number of mature individuals of the species is:

and either:

Clause 9 Low number of mature individuals of species

The total number of mature individuals of the species is observed, estimated or inferred to be:

Associate Professor Michelle Leishman
Chairperson
Scientific Committee

Proposed Gazettal date: 17/08/12
Exhibition period: 17/08/12 – 12/10/12

References:

Carlile N, Priddel D, Honan P (2009) The recovery program for the Lord Howe Island Phasmid (Dryococelus australis) following its rediscovery. Ecological Management and Restoration 10, 124-128.

Edgecombe J (1987) ‘Lord Howe Island: World Heritage Area’ (Australian Environmental Publications, Balmain, Australia)

Gurney AB (1947) Some notes on remarkable Australian walkingsticks, including a synopsois of the genus Extatosoma (Orthoptera: Phasmatidae). Annals of the Entomological Society of America 40, 373-396.

Hindwood KA (1938) The extinct birds of Lord Howe Island. Australian Museum Magazine 6, 319.

Honan P (2008) Notes on the biology, captive management and conservation status of the Lord Howe Island Stick Insect (Dryococelus australis) (Phasmatodea). Journal of Insect Conservation 12, 399-413.

Hutton I (1998) ‘The Australian Geographic Book of Lord Howe Island’. (Australian Geographic, Terrey Hills, Australia)

IUCN Standards and Petitions Subcommittee (2010) ‘Guidelines for Using the IUCN Red List Categories and Criteria Version 8.1.’ Prepared by the Standards and Petitions Subcommittee in March 2010.

Paramonov S J (1963) Lord Howe Island: a riddle of the Pacific, Part III. Pacific Science 17, 361-373.

Priddel D, Carlile N, Humphrey M, Fellenberg S, Hiscox D (2003) Rediscovery of the 'extinct' Lord Howe Island stick-insect (Dryococelus australis (Montrouzier)) (Phasmatodea) and recommendations for its conservation. Biodiversity Conservation 12, 1391-1403.