Another mode of life in armoured scale insects (Sternorrhyncha : Coccoidea : Diaspididae).

Thecatosoma, n.g., is proposed and T. caudatum (type-species), T. verticale, T. auriculatum, T. gracile, and T. crenatum, n.spp., are described from eastern tropical Asia (Palawan; Malaya; Borneo). The adult females of these scale insects are peculiar in having at maturity the head, all the thoracic segments, and the first abdominal segment coalescent to form an elongate sheath-like structure or ‘theca’, which is heavily sclerotized on the dorsal surface and along the body margin on the ventral side. They represent the ‘thecate’ mode of life, which is associated with ovoviviparity, the theca supplying a space with a tough cover for eggs developing into the nymphal stage within the maternal body. Excepting the formation of the theca, Thecatosoma is very similar to Unaspis, and should have originated from the latter. T. auriculatum in the pre-thecate state of the adult female is even undistinguishable from Unaspis and, in addition, finds a very similar species in Unaspis. These facts suggest the possibility that Thecatosoma is not a distinct genus but an aggregate of thecate forms of Unaspis, these forms being not necessarily closely related to each other. However, Thecatosoma as represented by the five species has the morphological variation much broader than in Unaspis in spite of the much fewer species. These species as a whole should not be the same as Unaspis in some biological aspects and, accordingly, in evolutionary potential, further species being expected to show a broader variation