The Oriental helotrephid genus Idiotrephes Lundblad, 1933, is taxonomically revised. Species discrimination is based on male genitalia and female terminalia. Three species groups are recognized. The I. chinai group contains I. chinai Lundblad, 1933 (type species; from Sumatra, Borneo, and West Malaysia) and three newly described species; I. asiaticus sp. n. (from Vietnam, Thailand, and west Malaysia); I. yupae sp. n., and I. polhemusi sp. n. (both from Thailand). The I. maior group contains I. maior Papáček, 1994; I. meszarosi Papáček, 1995 (both from Vietnam), and I. hainanensis sp. n. (from Hainan, China). The I. thai group consists of two newly described species from north and northeast Thailand, I. thai sp. n. and I. shepardi sp. n. In addition, some features of biology and morphology of the ovipositor are also included.
Some features of the biology and feeding relationships of small waterbugs (Notonectidae, Corixidae, Pleidae, Helotrephidae, Aphelocheiridae) and ripicolous bugs (Gelastocoridae, Ochteridae) are reviewed. Individual families are discussed as predators or as prey of other animals. Special attention is given to characteristics and relationships that affect human beings directly or indirectly. The most important relationships from the economic point of view are: bugs and blood-sucking Diptera, bugs and fish, bugs and some endangered or protected amphibians and water birds. Of less importance is the occasional use of some aquatic bugs as saprobity bioindicators. It seems that the economic importance of these bugs has been underestimated.