That's a good question when they are bright blue iridescent colour! Other Pollanisus spp. seem to have markedy different colouration, but I have to admit I have not seen a full collection of set specimens of Pollanisus so I am just relying on digital images. From the images of blue Pollanisus on your website and the relevant ALA webpage all the images of P. viridipulverulentus seem to have blue heads also, whereas P. apicalis seems to have a black head with a distinct blue 'face' as seen from above. I ruled out P. apicalis in this case on that basis. (both have been recorded int he ACT). However I can see that Pollanisus sp. (genus) may be seen as the safer option.
In Pollanisus species: does the shade of cyan between green and blue depend on the lighting angle? BOLD seems to have found 32 Australian Pollanisus species, including several unnamed ones that could be shiny cyan ones, given how easily they lose their scales, so I have doubts about all photos identified as Pollanisus viridipulverulentus, including the ones on the Coffs Harbour Butterfly House webpage, but then I haven't yet bought Gerhard Tarmann's 'Zygaenid moths of Australia', It's time to buy a copy I think.
P. viridipulverulentus is generally the largest species with the broadest wings, but it does have small specimens. P. apicalis is also bright blue-green when fresh, but is conversely smaller with narrower wings. I believe all of the reports we have allocated to P. vir. are one of these species and we can't reliably tell them apart unless a broad or narrow forewing shows up clearly. Those we have in P, sp are probably also these species, although the bright blue green can show up at the right angle for other V. species for which ACT is in range. We probably should merge them into one group with a species description along the lines of this comment.
Seems appropriate to merge P. vir... and P. apicalis when broad vs narrow wings can’t be determined. But it would slso be good to see ‘type’ images of P. vir... and P. apicalis when they can be distinguished. It seems head colour is not diagnostic.