Possible rescue from extinction: Transfer of a rare New Zealand tusked weta to islands in the Mercury group

Abstract

The rare Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), a large flightless insect originally confined to 13 ha Middle Island in the Mercury Islands, New Zealand, was last seen there in January 2001. Half-grown or larger insects from a captive-breeding programme were released onto nearby Red Mercury Island (34 ♀, 16 ♂) and Double Island (65 ♀, 19 ♂) in 2000 and 2001 to reduce the potential for accidental extinction. Most (108) were released under individual artificial cover objects (ACOs)-clear Perspex discs under plastic plant-pot saucers- and 26 were placed in artificial holes in soil. Usually <10% were found again under ACOs for up to 18 months including 7.5 months as adults. Adults, found in 2005 and 2006, were 1st to 3rd generation island-bred weta (lifespan 1.7-3.2 years). Ongoing monitoring is planned to confirm long-term success. Inbreeding depression is likely so supplementation from Middle Island is required but they may be extinct there. Scraping the soil to expose weta in underground galleries was the best monitoring method. Few were found by searching with lights at night but adults could be located by following other adults equipped with harmonic radar transponders or micro-transmitters.