Population expansion by Cook Strait giant wētā, Deinacrida rugosa (Orthoptera: Anostostomatidae), following translocation to Matiu/Somes Island, New Zealand, and subsequent changes in abundance

Abstract

Wētā, large wingless anostostomatid orthopterans, have been the most frequently translocated insects in New Zealand. Until recently, such translocations were only monitored intermittently to confirm presence. We investigate the spread of Cook Strait giant wētā (Deinacrida rugosa Buller, 1871) after its release on Matiu/Somes Island, Wellington, New Zealand, in 1996. Adult wētā were surveyed from 2008 to 2016 using footprint tracking tunnels and/or searching with spotlights at night. The population underwent a reversal in distributional abundance after 2008. In 2008, they were abundant in the north and rare in the south but by 2013 and 2015 they were relatively less abundant in the north and common in the south. Why they diminished in the north remains unknown but possible causes are predation on juvenile wētā by nocturnal geckos (detected in the north and east but not in the south), by some habitat change (mostly reduction of some lawn), or by a combination of these together with removal of wētā from the north for translocation elsewhere. Further research is required to confirm which of these factors affect wētā abundance, if there are other causes, and if any further change in distributional abundance occurs.