Two new species of Fergusobia, collected from small multilocular axillary vegetative bud ('stem') and unilocular leaf 'pea' galls on, respectively, Eucalyptus camaldulensis from South Australia, and an unknown species of Corymbia growing in sub-coastal north-eastern NSW, Australia, are described. Fergusobia camaldulensae n. sp. Davies is characterized morphologically by an almost straight to open-C shaped parthenogenetic female with a broadly conoid tail, an arcuate infective female with a hemispherical tail tip, and males of varying shape with weakly sclerotised angular spicules and bursa arising at mid-body length. Fergusobia rileyi n. sp. Davies is characterized morphologically by the combination of an almost straight to arcuate parthenogenetic female with a broadly conoid tail, an arcuate infective female with relatively narrow tail with a pointed tip, and arcuate males with arcuate spicules, a relatively slender tail, and long peloderan bursa. These species are associated with larvae of undescribed fly species having dorsal shields of the 'transverse bars' form or lacking. Other apparently related forms of Fergusobia/Fergusonina associations from small 'stem' and 'shoot' galls and unilocular leaf 'pea' galls are reported, the larval shield morphology of their associated mutualistic fly species is discussed where known, and their possible relationships are outlined. DNA sequence analyses of the domain 2 and 3 segments of the large subunit rDNA gene (D2/D3) and mitochondrial DNA cytochrome oxidase subunit 1 (mtCOI) supported the new species status and their phylogenetic relationships with other sequenced species in Fergusobia.
