Taxonomic and ecological studies of the Tasmanian Eucalyptus-defoliating paropsids (coleoptera: chrysomelidae), with particular reference to Chrysophtharta bimaculata (Olivier)
Creators: name: De Little, DW
Publisher: name: University Of Tasmania
Year: 2023

description: This study investigates the taxonomy and ecological relationships of the Tasmanian Eucalyptus-defoliating paropsid beetles of the family Chrysomelidae. In particular, the host-plant relationships, life history and population ecology of Chrysophtharta bimaculata (Olivier) a major forest pest in Tasmania, are investigated. A survey of eucalypt forest and woodland over much of the island revealed the presence of at least thirty-six paropsid species which fed on the foliage of eucalypts. These species belonged to five genera, viz: Paropsis Olivier (sensu stricto) (nine species), Trachymela Weise (eight species), Chrysophtharta Weise (thirteen species), Paropsisterna Motschulsky (three species) and Sterromela Weise (three, or possibly four species). All species were described and indicated by a code, but it was only possible to positively identify twenty-three species. No attempt was made to name new species, since it was considered that in the absence of a recent revision of the entire paropsid fauna, this would only serve to increase nomenclatural confusion within the group. Keys to adults and fourth instar larvae are provided. Records of Eucalyptus species on which each species of Paropsis was found at each collecting locality are given. The Tasmanian island paropsid fauna on eucalypts is compared and contrasted to that of mainland Australia in the light of current limited knowledge. Ecological relationships of the more common paropsids are discussed in relation to r and K strategy and niche differentiation. The host-plant relationships of two very common, highly r-selected species, Chrysophtharta bimaculata and C. agricola (Chapuis) were studied in detail in the field, insectary and laboratory. C. bimaculata showed a field preference for Monocalyptus species of the series Obliquae, while C. agricola preferred Symphyomyrtus species. In laboratory larval feeding trials, C. bimaculata performed better on a Monocalyptus species (E. delegatensis) than on a Symphyomyrtus species (E. dalrympleana) while C. agricola performed equally well on both species. C. bimacutata developed faster but was a less efficient feeder than C. agricola on E. delgatensis. It was therefore inferred that C. bimaculata was more highly r-selected than C. agricola, competitively displacing the latter species from E. delegatensis. Detailed studies were made of the life history and population ecology of C. bimaculata. This species was shown to be univoltine at least in N.W. Tasmania,and not bivoltine as previously considered. Partial population budgets were prepared for three populations. A major mortality factor in populations of immature C. bimaculata was the predatory coccinellid, Cleobora mellyi Mulsant which accounted for up to 74 percent of egg mortality. Egg parasitization and larval parasitization by the braconid species Eadya paropsidis were described for the first time. The pest potential of C. bimaculata is discussed in the light of its host-plant relationships, ecological strategies of its preferred hosts, and other population determinants.