Several felt scale (Eriococcidae) lineages show deep, phylogenetically constrained, host use. The most diverse of these host-constrained lineages is Australian, associated with plants in the family Myrtaceae, and the most diverse sublineage within this group is associated with Eucalyptus. Here we use Bayesian analysis of morphological data to estimate relationships among the eucalypt-feeding species of this group. We identify an unusual species for which we erect the monotypic genus Heathcotia Hardy & Beardsley gen.n., with type species Heathcotia crypta Hardy & Beardsley sp.n., and recover a clade comprised of six new species closely related to Lachnodius hirtus Maskell. We erect the genus Lobimargo Hardy & Gullan gen.n. for the latter clade, designate Lobimargo sagittisetus Hardy & Beardsley sp.n. as its type species, transfer Lachnodius hirtus to the genus as Lobimargo hirtus (Maskell) comb.n. and describe the five other new species: Lobimargo brookesae Hardy & Beardsley sp.n.,Lobimargo donaldsoni Hardy & Gullan sp.n., Lobimargo latrobeus Hardy & Beardsley sp.n., Lobimargo rhipidotrichus Hardy & Gullan sp.n. and Lobimargo williamsi Hardy & Gullan sp.n. A lectotype is designated for L. hirtus. The adult female of each species, the first-instar nymph of L. sagittisetus, the second-instar female of L. hirtus and the adult male of L. williamsi are described and illustrated. A key is provided to the adult females of all eriococcid genera found on eucalypts and of all Lobimargo species. Adult females of Lobimargo have been found on stems, sometimes causing shallow pits, and on foliage or under bark, but may move to the latter habitat for oviposition.