Distinguished by the broad dark anterior fascia which is well separated from the anterior margin of the elytra; allied to M. pyritosa but larger in size, broader in shape, and with less intense red colouration and more greenish reflections. It is highly iridescent, and the non-pigmented areas of the elytra change from reddish to coppery-gold and to green with differing angles of view.

This species was described by Blackburn 1888a who cited specimens at the SA Museum including one 'taken by Mr. Tepper at Dimboola, Victoria' and another with 'no record of capture'.
Prior to May 2024, it was treated on these pages as Melobasis fasciata Carter, 1923, in accordance with determinations on most specimens of it in the SA Museum at that time, which match the description and the accompanying illustration in the protologue of M. fasciata by Carter 1923b. However, they also match type specimens of Melobasis pretiosa Blackburn 1888 at the SA Museum. Although the Dimboola specimen was not located, two presumed syntypes without locality were seen, each bearing a determination as M. pretiosa in Blackburn's handwriting and one annotated by Levey in 1974 as a [proposed] lectotype of M. pretiosa. The names M. pretiosa and M. fasciata clearly refer to the same taxon, and the earlier published name has priority, making M. pretiosa the correct name for this species.

Tepper 1887 (p. 16) may have been referring to this species when he wrote: 'The larva of this [M. sexplagiata], and some similarly tinted species, live in the old and very thick dead corky bark of redgum (Euc. rostrata) [=Eucalyptus camaldulensis], from which the writer has often extracted the beetles in early spring. The latter seldom frequent flowers, but are mostly found on the sunny side of the trunks or leaves of Eucalypts, and are active and wary in the hot sunshine, though sluggish on cloudy days.'

My surmise above on the identity of Tepper's beetle was verified in April 2024 when I found a dead non-emerged adult M. pretiosa in the old outer bark of a Red Gum. Further details are provided under 'Host plant notes' below. At that time M. pretiosa was represented in the SA Museum by only eight collections with SA localities, and only one collected after 1952. The species has since proved to be very abundant in the Adelaide region, particularly in the eastern suburbs and foothills.

This is a late-emerging species. The earliest emerged adult that I have seen in the Adelaide area was observed on a Red Gum trunk on 20th December, but I have obtained live non-emerged adults from early November.

Prior to 2024, I made and posted on this page the following speculative comments anticipating the breeding behaviour of M. pretiosa. 'An allied species from WA (from the same species-group) is well known for breeding in the bark of Eucalyptus rudis (Flooded Gum), a eucalypt that is closely related both phylogenetically and ecologically to the Red Gum. A single specimen of M. fasciata was observed alighting on the trunk of a Red Gum (E. camaldulensis) in Adelaide by R.V. Glatz (pers. comm.). This, taken together with the fact that Red Gums are prominent at a number of the SA collection locations, suggests that M. fasciata [= M. pretiosa] may breed in the thick basal bark of that eucalypt.'

This postulation led me to search the trunks of Red Gums, and in April 2024 I discovered the remains of a dead non-emerged adult M. pretiosa in some old outer bark that I had removed from a Red Gum trunk at Brownhill Creek in Adelaide on December 2021. The bark had lenticular-elliptical exit holes that connected with meandering, flattened, frass-filled tunnels and broader excavations, as deep as 25 mm below the bark surface, but remaining within the bark layer and not penetrating the hardwood surface. Images of those adult remains lodged in the exit tunnel are presented here (the first six dead adult images under 'Breeding record images' illustrate that specimen, PL6130).

Subsequently I found further specimens at other sites and also live larvae, which again were confined within the dead tissue of the bark layer. A consequence of this specialised larval feeding behaviour is that breeding of M. pretiosa in Red Gums can be easily recognised by the presence of the characteristic exit holes and extensive frass-filled tunnels within the outer bark below them. As the bark tissue is dead, the exit holes do not become grown-over and appear to remain evident and well-preserved for many years. In Red Gums the old bark can persist on the base of the tree for decades. The holes measure 3.4 to 5.4 mm across by 2.2 to 3.8 mm wide (mean 4.5 x 2.9 mm, n = 48). On a single tree in Myrtlebank I counted 165 exit holes.

It seems that M. pretiosa has remained a common species in the Adelaide area, despite the intensive urban and suburban development, because its principal host, Red Gum E. camaldulensis, are long-lived and popular trees that have been widely retained along creeks and adjoining areas.

The related M. pretiosa species-group taxon breeding in E. rudis bark in WA is now known to be M. pyritosa - q.v., rather than M. sexplagiata as it was called for many years; the latter is a species apparently confined to NSW (- thanks to Brian Levey (pers. comm., Apr 2024) for this information). The parallel behaviour of breeding in retained thickened bark on trunks of Eucalypts is a significant specialisation, and it would be of interest to know whether it applies in other members of the M. pretiosa species-group.

I July 2024, A.M.P. Stolarsksi extracted dead remains from a rough-barked Eucalypt in Black Hill Conservation Park, which I visited and identified as a hybrid between Mallee Box Eucalyptus porosa and SA Blue Gum E. leucoxylon ssp. leucoxylon. Several apparent F1 hybrids were present nearby, but the host tree appears morphologically closer to E. porosa, although differing in its coarser more fibrous bark, and is more likely an F2 hybrid or backcross with E. porosa. The beetle (PL6143) and host tree (PJL 3782) are illustrated here.