This is a small family of some 25 world species in the genera Cryptochetum and Librella (McAlpine 1976). The species of Cryptochetum are mostly tropical and subtropical and originate in the Old World (Cogan
  1980b). They are recorded within the Australasian/Oceanian Regions only
  from Australia, New Zealand, and the Hawaiian Islands.
  
  The larvae of Cryptochetum are internal parasitoids of monophlebine
  coccids and have been used successfully to control coccid pests of cultivated
  plants such as citrus and pine. Two of the 4 Australian species have been
  introduced to North America (Colless & McAlpine 1970), and one of these
  subsequently to Chile (Prado 1975) to control scale insects. Detailed information
  on the life histories of Cryptochetum species is given by Thorpe
  (1931, 1934, 1941a,b). The adults of some species are obnoxious as "eye
  gnats" in India, Japan, and the Philippines (Nartshuk 1984). Nothing
  is known of the life history of Librella demetrius.
  Refs.: Thorpe (1931, 1934, 1941a,b, life history), Ferrar (1987,
  immat. biol.).
CRYPTOCHETUM Rondani, 1875a: 167, 190. Type species: Cryptochetum
  grandicorne Rondani, 1875, orig. des.
  CRYPTOCHOETUM. Incorr. orig. spell. of Cryptochetum (Rondani,
  1875a: 172).
  LESTOPHONUS Williston, 1888: 21. Type species: Lestophonus iceryae Williston, 1888, mon.
  CRYPTOCHAETUM, error for Cryptochetum.
  iceryae Williston, 1888: 21 (Lestophonus). Australia (?SA);
  Hawaiian Is, NZ (NZ) [introduced]; N. & S. Am. [introduced], Afrotrop.
  Reg.
LIBRELLA McAlpine, 1976: 45. Type species: Librella demetrius McAlpine, 1976, orig. des.
    demetrius McAlpine, 1976: 46. Australia (NSW); Australia (ACT).