Threats to the critically endangered Arid Bronze Azure butterfly (Ogyris subterrestris petrina) by proposed vegetation clearing Matthew R. Williams, Senior Research Scientist, DEC Science Division. Andrew A. E. Williams, Senior Technical Officer, DEC Science Division. 4 November 2008 Summary The critically endangered Arid Bronze Azure butterfly (Ogyris subterrestris petrina Field 1999) has been recorded from only two localities, both in south-west Western Australia. No butterflies have been seen at one locality since 1993 and this population is considered extinct. The habitat of the remaining population, in remnant vegetation adjacent to Barbalin Nature Reserve, is subject to a clearing application. This report (i) records the significance of this site to the long-term survival of the butterfly; (ii) examines the likely effect of clearing and associated disturbance on the butterfly population; (iii) documents the surveys that have been conducted for this butterfly; (iv) discusses any potential for other populations to occur in the region; and (v) examines the likelihood that the butterfly population, if displaced, could disperse and colonise other sites nearby. 1 Introduction The butterfly. The Arid bronze Azure butterfly (Ogyris subterrestris petrina) is a medium-sized, robust butterfly capable of rapid flight (Figures 1, 2). It is predominantly dark brown to black, with bronze to purple-bronze colouration on the uppersides of the wings. The underside is grey-brown, with iridescent bluish-white bars in the forewing cell and a series of brown-black markings on the hindwing. It has pronounced sexual dimorphism: males have dull dark-purplish bronze uppersides whereas females have purplish areas on the uppersides of both wings and a cream patch on the forewing. This butterfly is readily identifiable because it has several distinctive features: (i) a very rapid and direct flight pattern, characteristic of the genus; (ii) uniquely for butterflies in the region, a very dark colouration (adults, especially males, appear almost black in flight); (iii) a habit of perching on the ground in open areas (including on roads and roadsides); and (iv) are among the largest lycaenid butterflies in Australia. These characteristics make Ogyris butterflies easily identifiable in the field, to the extent that populations have been detected from vehicles. The Barbalin population of O. s. petrina was discovered in this way when an amateur entomologist drove through the site and recognised the butterflies as Ogyris sp. as they flew across the road. More than 400 species of butterflies are recorded for Australia and few more are likely to be discovered, making them the best-known insect group (Braby 2000). Members of the genus Ogyris are large and spectacular lycaenid butterflies that are restricted to the Australian region. Of the 13 species in Australia, 10 were discovered before 1900 and remainder between 1900 and 1914. The last species to be described, O. subterrestris, was discovered in 1912 but was so rare that it was not described as a distinct species until extant colonies were discovered in the 1980s. No butterfly species of comparable size has been discovered in Western Australia since 1913. Because of their relatively large size and often spectacular colouration, Ogyris species are prized by butterfly collectors who actively seek out populations. Occurrence of most species is highly localised. The larvae are attended by ants and feed mainly on mistletoes and 2 related parasitic plants but two species (O. idmo and O. subterrestris) are myrmecophagous, feeding exclusively on the larvae and pupae of the attendant ants. The Arid bronze Azure was described from a series of 72 specimens collected between 1982 and 1991 at Lake Douglas, 12 km SW of Kalgoorlie, Western Australia. The holotype female was collected at this site by Ross Field on 12 Nov 1989 (Museum of Victoria accession number NMV T-17268). The new species was distinguished from the related species Ogyris idmo, O. otanes and O. waterhouseri by a series of morphological traits. When described, O. subterrestris was recognised as comprising two subspecies: O. s. subterrestris (the Mallee Bronze Azure) from three extant localities in South Australia, New South Wales and Victoria, and O. s. petrina from the single locality in Western Australia. A subsequent study of mitochondrial DNA confirmed the taxonomic distinction between O. subterrestris and the related species, and also between the two subspecies of O. subterrestris (Schmidt et al. 2005). Based on molecular clock methods, Schmidt et al. (2005) concluded that the two subspecies had diverged between 3 and 4 million years ago. In order to reproduce, the butterfly has an obligate association with a single form of one species of ant, the pale-coloured or ‘Goldfields’ form of Camponotus terebrans. The larvae (Figure 3) are fed by or predate the ants and live entirely within the ant’s nest during their development (Field 1999). Studies of other ant-dependent butterfly species have shown that a certain number and density of ant colonies is required in an area before the site can support a breeding colony of butterflies: an approximate ratio of ants to butterflies is 500 to 1 (Griebeler & Seitz 2002). Where the butterfly occurs, the ant colonies are enormous (R. Grund, Butterflies of South Australia website: http://users.sa.chariot.net.au/~rbg/subterrestris_ds.htm). Male butterflies typically form small flight areas or territories (leks), approximately 5-20m in extent, adjacent to the breeding area. They patrol these leks and defend them against other males. Males also establish territories on hilltops if these are near the breeding area, a common behaviour amongst butterflies. Unmated females visit the leks or hilltops to mate, but thereafter practice male avoidance and remain within the breeding area to lay eggs. Most of the eggs are probably laid in the original breeding area, but some females probably disperse to search for new breeding areas. This is the usual life history pattern amongst ant-tended 3 lycaenid butterflies (Pierce et al. 2002). Typically, each female lays more than half of her eggs in the original colony and dispersal commences thereafter. If successful in locating another ant population these dispersals may result in the establishment of new butterfly colonies. Typical dispersal distances are not known for females of O. s. subterrestris, but a study of a similar lycaenid butterfly in south-west Australia, Hypochrysops halyaetus, found that of over 1000 marked individuals the longest dispersal distance was 810 m for one female, but averaged less than 200 m (M. R. Williams, unpublished data). The butterflies are active and breed continuously between October and April. All life stages (eggs, larvae and adults) are present during this period. Between May and September, the entire population consists of larvae only, all of which are within ant colonies. There is a peak in butterfly numbers in October, when the over-wintering larvae complete the life cycle and emerge as adults. The Threatened Species Scientific Committee (TSSC) assessed the taxon as Critically Endangered (A3c, B1 + 2ab(i, ii, iii, iv, v)) and the butterfly was gazetted as Schedule 1 (rare or likely to become extinct) in August 2008 (Government Gazette 5 August 2008, p 3483). Known populations. A single specimen of O. s. petrina was collected in October 1912 from the ‘Kalgoorlie District’ and lodged in the British Museum. No further specimens were known until Prof. Alan Graham of the WA School of Mines in 1982 discovered a population at Lake Douglas, 12 km SW of Kalgoorlie. Prof. Graham conducted regular (typically weekly) visits to the site and collected several specimens. These were provided to the Australian National Insect Collection, which confirmed that the butterfly represented a known but undescribed species of Ogyris. Several professional and amateur entomologists also visited the site during 1982 – 1992 and collected specimens which are held in private and public collections. At Lake Douglas the butterfly occurred intermittently over a large area, approximately 3 x 1.5 km. Butterflies were locally abundant at the site between 1982 and 1991, but in 1992 underwent a severe decline. Prof. Graham observed only two individuals in 1993 and no 4 butterflies have been seen at the site since then, despite numerous visits by both amateur and professional entomologists (Table 1). Table 1. Known searches for Ogyris subterrestris petrina at the Lake Douglas site between 1993 and 2007. Date(s) Observer(s) Time spent at Survey method Results the site 1993-2002 A Graham Weekly visits Walk surveys No butterflies seen Oct 1992 M Williams & 1 day Walk surveys No butterflies seen R Hay Oct 1994 M Williams & 1 day Walk surveys No butterflies seen R Hay Oct 1995 M Williams, 2 days Walk surveys No butterflies seen R Hay & T Lundstrom Oct 1997 S Johnson & 2 days Walk surveys No butterflies seen P Valentine Oct 2000 M Williams, 2 days Walk surveys No butterflies seen A Williams, D Lohman & A Graham Oct 2001 S Brown & 1 day Walk surveys No butterflies seen R Weir Oct 2002 J Landy 1 day Walk surveys No butterflies seen Oct 2003 J Landy 1 day Walk surveys No butterflies seen Oct 2003 P Samson 2 days Walk surveys No butterflies seen Oct 2003 A Williams 2 days 2 x 3km structured No butterflies seen walk transect surveys Dec 2003 A Williams 2 days 2 x 3km structured No butterflies seen walk transect surveys Apr 2004 A Williams 2 days 2 x 3km structured No butterflies seen walk transect surveys Nov 2005 J Landy 1 day Walk surveys No butterflies seen Oct 2007 S Brown, 1 day Walk surveys No butterflies seen G Miller The surrounding areas have also been searched extensively but no butterflies have been seen. In particular, during the period that he resided in Kalgoorlie between 1982 and 2002, Prof. Graham undertook numerous field trips into the surrounding areas.