Aquatic and semi-aquatic true bugs (Hemiptera, Heteroptera) are highly abundant in both lentic and lotic systems in Thailand. More than 230 species representing 12 families of these insects have been reported from freshwater habitats in Thailand. The Thai fauna has been studied intensively in the last several decades, but no research focuses on the species assemblages of aquatic and semi-aquatic true bugs in urban areas. Two important discoveries were found in this study: the species assemblages of aquatic and semi-aquatic true bugs of ponds in the green zones of Bangkok and their association with margin type (natural vs. artificial).The complete taxonomic list of aquatic and semi-aquatic true bugs from 28 ponds in the green zones is presented. Twenty species representing 16 genera, 12 families and two infraorders are reported in this study. More specially, nine species, seven genera and four families of Gerromorpha and eleven species, eight genera and seven families of Nepomorpha were collected. Although the number species of this research accounts for only 9% of the Thai fauna, the study area represented less than 0.01% of total land area in Thailand. Overall, Cluster Analysis and Principal Component Analysis showed species compositional dissimilarities between ponds with natural margins and ponds with artificial margins. In general, species richness, especially members of Nepomorpha in ponds with natural margins, is higher than those in ponds with artificial margins. This finding is valuable for aquatic system management to promote a higher diversity of aquatic insects in the green zones of urban areas in Thailand.
