Emma Curtin & Barbara Barratt

The extraordinary story of an unassuming beetle: the past, present and future of the Cromwell chafer beetle

Curtin, E.R.1, Barratt, B.I.P2. & McKinlay, B.3 

1 University of Otago, Department of Zoology, Address, Dunedin, New Zealand. email: emma.curtin@postgrad.otago.ac.nz
2 AgResearch Invermay, Biocontrol, Biosecurity and Bioprocessing, Puddle Alley, Mosgiel PB 50034, New Zealand. email: barbara.barratt@agresearch.co.nz
3 Department of Conservation, John Wickliffe House Level 1/265 Princes Street, Dunedin, New Zealand. email: bmckinlay@doc.govt.nz

The Cromwell chafer beetle, Prodontria lewisii, is a critically endangered species, with the entire population restricted to an 81ha reserve in Central Otago, New Zealand. The Cromwell chafer is the only insect in the southern hemisphere with its own reserve, making both it and its habitat unique. Here we will describe the history of Reserve and the Cromwell chafer itself, from the discovery of the beetle in 1903, through to the creation of the Reserve in 1983 and onwards to the research taking place in the present day. The Department of Conservation manage the reserve and we describe how research informs current and future management. The results of ongoing monitoring efforts have shown that despite multiple threats in the form of dam building, introduced predators and habitat destruction, the population has remained relatively stable since 2001. However, the threats facing the beetle are changing over time and new threats are emerging. Redback spiders were first observed on the Reserve in 2008 and a single spider is capable of killing over 40 beetles. Spider surveys have shown that manually filling in rabbit burrows deprives redbacks of their favoured web-building habitat and leads to a reduction in chafer beetle deaths. As well as providing habitat for invertebrate pests, mammals – including humans – pose threats in themselves. We examine these pressures in turn and detail the studies undertaken to date to understand each of them. We also explore the possibility of translocating the Cromwell chafer beetle to alternative habitat outside the Reserve. A study aiming to identify key plant and soil types for optimum larval and adult survival using both field and laboratory raising experiments has shown that the Cromwell chafer is highly habitat-specific, requiring particular soil and plant combinations in order to thrive. We aim to provide a holistic picture of this special species – its unusual past, threats to its present, and hopes for its future.

The next generation of Prodontria lewisii in the making. Photo taken on the Cromwell Chafer Beetle Nature Reserve by ER Curtin.