Abstract
This is Part I of a series of three papers wherein five species groups sharing an identical chaetotaxy of the dorsal setae in the genus Typhlodromus Scheuten are described. A key to the adult females of the five species groups is provided. Two species groups, regularis and theodoliticus, are described and discussed in detail as the first of the series. Generic concepts of various authors in relation to the species belonging to the two groups are outlined and a key to and descriptions of adult females of each species in the two groups is presented. Amblyseius pritchardi Chant and Baker, which was erroneously placed in the genus Amblyseius Berlese, is transferred to the genus Typhlodromus.