The larval species of the family Achaemenothrombiidae have been described only from Iran and they are known as parasites of Lepidoptera (Noctuidae) and Orthoptera (Acrididae). Achaemenothrombium saboorii Noei sp. nov. (Trombidiformes: Trombidioidea: Achaemenothrombiidae) is described and illustrated. The families Crambidae, Erebidae, Geometridae (Lepidoptera), and Tettigoniidae (Orthoptera) are recorded as hosts of Achaemenothrombium larvae for the first time from South Khorasan province, Iran. Also, the generic diagnosis of the genus Achaemenothrombium is amended and a key to larvae is updated.