GROWTH OF 3 SPECIES OF BIBIO (DIPTERA, BIBIONIDAE) LARVAE UNDER ALPINE CONDITIONS IN NORWAY

Semivoltine life cycles are described for the larvae of Bibio rufipes and Bibio siebkei at altitudes of 1225-1275 m on Hardangervidda, South Norway. At this altitude the larvae develop through seven instars in two years. The growth pattern of larvae of Bibio pomonae from an altit ude of 1310 m is also consistent with a development time of more than one year, although young larvae of this species were not collected. Dr y weights of the larvae were measured, End the growth pattern was rela ted to ground temperature. The larval developments of Bibio rufipes an d B. siebkei were found to take approximately 1800 degree-days above 0 degrees C. Densities of larvae were estimated from field samples, and circumstantial evidence for a variable life-cycle length is presented and discussed.