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These are dead galls of males on the gall of a female. In Apiomorpha munita, males induce galls only on galls of females.
Correct ID. We're working on the taxonomy of this "species" and eventually it will be split into multiple different species. Currently there are three subspecies recognised: A. munita munita on red gums, grey gums and maidenarias; A. munita tereticornuta on boxes and ironbarks, and A. munita malleensis on mallees. The galls can look the same and are somewhat dependent on the host eucalyptus species.
Adult females of A. munita can live up to five years, and even years after the gall in which she lives has dried out.
The galls are induced on new vegetative growth (new branchlets) rather than cones, and they can grow on male and female plants (many Allocasuarina species have separate sexes, and cones are only on females). One of the identifying features of the host plant species is the number of scale-like leaves around the nodes of branchlets, and the galls make them easy to count - the number of bracts in each ring on the gall is the same as the number of tiny leaves around a branch node.
Galls look like those found on Lophostemon (brush box).
The "two kinds" of scale insect on the acacia are actually males and females of the one species. The smaller white scales are the covers of males - they have an opening after the winged male leaves. The larger brown globular scales are old females - they stay where they begin to feed and die in situ.
These are lerps - excretions of psyllids (Psylloidea) that cover the insect..
Probably not Mesostoa kerri. The website link Martin provided has images similar to this, and the website indicates this to be the causative species. However, if you follow the link to CSIRO, which is given as a source for identification, it leads to a paper about this species. The galls shown in the scientific paper are quite different and show that M. kerri affect the stem, rather than the inflorescence.
The galls are not those of males of Apiomorpha karschi, which are much smaller than those of A. strombylosa and a bit different in shape. Relative to the mid-vein of the leaves in the photos, the galls are far too big to be those of A. karschi.
These scale insects make a lot of honeydew and they provide a food source for many other insects (wasps, bees, flies etc) and birds, in addition to ants. I've seen honeyeaters licking them like a lollypop.
