The biogeography and host plant utilisation of eucalypt feeding Coreidae (Hemiptera: Heteroptera)
Creators: name: Steinbauer, MJ
Publisher: name: University Of Tasmania
Year: 2023

description: In Tasmania, Australia, the family Coreidae (Hemiptera: Heteroptera) is represented by three species; Amorbus obscuricomis (Westwood), Gelonus tasmanicus (Le Guillou) and Acantholybas kirkaldyi Bergroth. Of these, A. obscuricomis and G. tasmanicus are host specific for plants of the genus Eucalyptus (Myrtaceae), with the former feeding almost exclusively upon shoots and the latter feeding at various sites. Initial uncertainty as to the identity of the coreids within Tasmania lead to the taxonomy of the three genera being reyiewed. These studies showed that Amorbus, a genus of 20 plus species, is represented in Tasmania only by A. obscuricomis; while Gelonus tasmanicus was confirmed as being a monospecific genus. Rediscovery of individuals of A. kirkaldyi, known previously only from the type description, allowed a formal revision of this genus to be undertaken. The distributions of A. obscuricomis and G. tasmanicus were found to include much of Tasmania and south-eastern Australia. In Tasmania, coreids were noticeably absent from the western half of the island where the vegetation is almost devoid of eucalypts. Both species were found to be univoltine in Tasmania. The phenology of A. obscuricomis appears to coincide particularly well with seasonal growth phenology of Eucalyptus. Aspects of these species' developmental and reproductive biologies are used to support hypotheses concerning their biogeography and host plant utilisation. No-choice host plant performance studies revealed that A. obscuricomis would feed and lay eggs on all Eucalyptus species offered. Nymphs of this species were also able to eclose on most eucalypts tested. G. tasmanicus was only able to reach adulthood on E. regnans and E. delegatensis. For A. obscuricomis, performance indicators such as adult survival, egg production and weight of offspring were influenced by the quality of the hosts' shoots, in particular the C/N ratio and water content; while the reduced host range of G. tasmanicus is suggestive of a more important role of secondary plant substances in the species. The oligophagous habit of A. obscuricomis and G. tasmanicus for eucalypts was confirmed by field sampling. General observations suggested that A. obscuricomis preferred hosts which were coppicing after being physically damaged and a field based experiment investigated this issue. Epicormic buds were induced by canopy removal, simulating the effect of fire. Sampling of control and coppicing eucalypts revealed the complete absence of A. obscuricomis nymphs from non-coppicing trees. C/N and water content analyses of coppicing and control hosts revealed that coppice shoots were nutritionally superior to normal shoots. In the discussion I relate the biogeography and host plant utilisation of A. obscuricomis, in particular, to the degree of polyphagy exhibited by that species. I argue that the selection pressure imposed on A. obscuricomis by an environment where the supply and quality of eucalypt shoots is unpredictable, has favoured the evolution of an oligophagous feeding strategy. That the species is oligophagous for plants belonging to the one genus is possible given the ubiquity of Eucalyptus species in the Australian environment.