Assessment of the ecological risk posed by the exotic rhinoceros beetle chalcosoma chiron chiron for the Japanese horned beetle trypoxylus dichotoma septentrionalis

Abstract

Many exotic stag and rhinoceros beetles are imported to Japan every year. This has raised various issues, such as competition and hybridization between exotic and native taxa, and experimental verification of this has been reported. However, most reports focus on exotic stag beetles, and the rhinoceros beetles have received little attention. It is necessary to perform the same risk assessment for rhinoceros beetles as has been done for stag beetles. This study examined whether the exotic rhinoceros beetle Chalcosoma chiron chiron can establish itself in Japan and whether it will compete with the Japanese horned beetle Trypoxylus dichotoma septentrionalis, affecting its feeding behavior. Adult C. chiron chiron survived at an equal rate with T. dichotoma septentrionalis, and C. chiron chiron also laid eggs in the field and fed on the sap of Quercus serrata. Although the eggs hatched, the larvae could not survive the winter. The activity time of male C. chiron chiron overlapped that of male T. dichotoma septentrionalis. When fighting, C. chiron chiron usually defeated T. dichotoma septentrionalis. These results suggest that the possibility of C. chiron chiron becoming established in Japan is low, but this species competes with T. dichotoma septentrionalis and affects its feeding behavior.