Do Exotic Versus Native Grasses or Increasing Plant Diversity Affect Larval Development of the Cromwell Chafer Beetle ( Prodontria lewisii )?

The Cromwell Chafer Beetle ( Prodontria lewisii ) is an endangered flightless scarab that is extremely vulnerable to extinction because of its small single population at the Cromwell Chafer Beetle Nature Reserve. Captive rearing and translocation are being tested as additional tools to support existing conservation management of this species. To optimize both, a better understanding of factors supporting larval development are required. This study investigates variation in development rates and survival over a 6‐month period when larvae were reared on an exotic vs. a native grass ( Anthoxanthum odoratum and Rytidosperma maculatum ) and either with or without the addition of an exotic herbaceous plant ( Rumex acetosella ). Both grasses successfully supported the growth and survival of P. lewisii larvae. There was no significant difference in either monthly or overall weight change between larvae reared on the plant combinations tested. Survival did not vary significantly between larvae reared on the exotic vs the native grass (60% vs. 67% survival) and there was no significant difference in mortality risk. However, in the presence of the herb Ru. acetosella , survival of larvae reared on the exotic grass increased from 60% to 86%. This equated to a significant 3.7‐fold increase in mortality risk for larvae reared on the exotic grass in the absence of Ru. acetosella compared to those with the herb present and supports the hypothesis that diet diversity may benefit the development of larvae.