Unsuccessful search for further specimens of the giant knobbled weevil Hadramphus stilbocarpae (Curculionidae: Molytinae: Molytini) at East Ruggedy on mainland Stewart Island

Abstract

On the 14th December 2011 I returned to East Ruggedy Beach on Stewart Island to search for further specimens of Hadramphus stilbocarpae (Kuschel 1971) after finding the first specimen of H. stilbocarpae and the tribe Molyini on mainland Stewart Island dead, on sand roughly 1 km inland in December 2008. Although my latest search for this weevil was unsuccessful, I found its food plant Anisotome lyallii (Apiaceae), growing both on the coastal cliffs at the Southern end of the beach and also at the Southern end of Little Helfire Beach. However, no further evidence of H. stilbocarpae was found on the few plants that were accessible. Many of the plants visible could only be reachable by abseiling, most likely a result of heavy grazing by deer, several of which were seen nearby. Since only a minute portion of the Ruggedy Coast was examined it is still possible that a small population may survive on the mainland. However deer are abundant in the area and graze on A. lyallii. Further, rats, known predators of H. stilbocarpae, occur on mainland Stewart Island, and this must greatly threaten the knobbed weevil here, particularly since Meads has noted that the weevil's presence or absence is a good indicator of whether or not there are rats on an island. This may indicate the specimen I found may have been preserved in the sand and the mainland population is now extinct. The Rugged Islands located 1-2km offshore may be a refuge for Stewart Island H. stilbocarpae as it is unlikely deer are present there although Maori did visit on their way to the Southern Titi Islands who could have introduced Kiore to the islands but as to date no specimens have been collected there.