‘Rhyzobius ventrails’ (Coleoptera: Coccinellidae), its constituent species, and their taxonomy and historical roles in biological control

The Rhyzobius (or Lindorus) ventralis frequently referred to in the literature of biological control is shown to be a mixture of two distinct, though similar, species. The origin of the confusion is traced to the nineteenth century searches in Australia for insects to control scale insect infestations on citrus and other crops in California. Adults of the two species are defined and illustrated, and a key is provided for their separation. Lectotypes are designated for R. ventralis (Erichs.), its synonym Scymnus restitutor Sharp and for S. halli Broun, newly synonymised with R. ventralis. A lectotype is designated for Platyomus forestieri Muls., the second species of the complex, here transferred to Rhyzobius, and for S. circularis Sharp, newly synonymised with R. forestieri. Distribution data for both species, based on actual specimens examined, are listed, and their Australian distribution is summarised in a map. Past usages of ‘ R. ventralis’ as a biological control agent are reviewed in the light of the revised taxonomy. The taxonomy and nomenclature of Rhyzobius Stephens is discussed in order to establish the correct generic placement of and binomina for R. ventralis and R. forestieri.