AbstractComplex subsociality involving guarding, progressive provisioning, and trophic egg production behaviours in herbivorous Hemiptera is known in only a few genera in the Cydnidae subfamily Sehirinae and in Parastrachiidae. Because progressive provisioning and trophic egg production are apparently specific to these closely related species, phylogenetically it seems likely that the behaviours emerged once in the common ancestor of this clade. However, the scarcity of information on species in the clade precludes any reliable exploration of this hypothesis. To ameliorate this situation, it is necessary to accumulate additional information for as many related species as possible. To this end, we first targeted Japanese representatives of the genus Adomerus Mulsant and Rey (Hemiptera: Cydnidae), three species of which are distributed in Japan. Complex subsocial behaviours in two of these species, Adomerus triguttulus (Motschulsky) and Adomerus variegatus (Signoret), have been well characterised and analysed. The third Japanese species, Adomerus rotundus (Hsiao), was identified to display complex maternal care, but, with the exception of egg hatch synchronisation, parental behaviours have not been characterised. In this study, we examined the parental behaviours of A. rotundus. Additional investigations on subsocial behaviours, in addition to morphological and molecular analyses, should gradually clarify whether the complex subsociality represents a homologous or convergent adaptation.