The Incidence and Relative Abundance of Amorbus obscuricornis and Gelonus tasmanicus (Hemiptera : Coreidae) in Southern Tasmania and Their Performance on Selected Eucalyptus Species

Abstract

Comprehensive records of the host-plant associations of Amorbus obscuricornis (Westwood) and Gelonus tasmanicus (Le Guillou), undertaken over three years at field sites in southern Tasmania, are presented for the first time. Also presented are the results of performance experiments conducted predominantly with native Tasmanian Eucalyptus species. Both insect species were found to be oligophagous for Eucalyptus. However, A. obscuricornis was found to feed more widely than G. tasmanicus; that is, the former species fed upon eucalypts belonging to the ash, gum and peppermint groups whilst the latter was confined to the ash and gum species of Eucalyptus in Tasmania. On the basis of collection records, A. obscuricornis was found to be abundant in both wet and dry sclerophyll forest habitats whilst G. tasmanicus was more abundant in wet sclerophyll forests. The wider degree of oligophagy exhibited by A. obscuricornis than by G. tasmanicus is suggested as being related to this species’ preference for floristically diverse habitats, for example dry sclerophyll forest. In addition, inter- and intraspecific host selection in the exclusively shoot- feeding A. obscuricornis was found to be positively influenced by the architecture, in particular the coppicing phenology, of hosts. The significance of factors such as plant architecture, resource abundance and nutritional quality to the host-plant associations of both species are discussed in relation to secondary chemistry and habitat preferences.