COLD-HARDINESS OF THE ELM BARK BEETLE SCOLYTUS-LAEVIS CHAPUIS, 1873 (COL, SCOLYTIDAE) AND ITS POTENTIAL AS DUTCH ELM DISEASE VECTOR IN THE NORTHERNMOST ELM FORESTS OF EUROPE

Cold hardiness was studied in overwintering larvae of the elm bark bee tle (Scolytus laevis) which is an important vector of the dutch elm di sease in northern Europe. Mean SCPs were as low as -29-degrees-C in mi d-winter and increased to -21-degrees-C in May. Corresponding melting points varied from -6.5 to -0.7-degrees-C with thermal hysteresis free zing points 0.2-0.3-degrees-C lower during the winter. Glycerol was th e main low molecular weight cryoprotectant substance. Frozen larvae be came active shortly after thawing, but subsequently died or were unabl e to pupate at 21-degrees-C. In the early part of the winier supercool ed larvae survived extended periods at -19-degrees-C but were killed a t this temperature in the s ring. It is concluded that cold hardiness will not be the limiting factor for the distribution of the elm bark b eetle within the limits of the elm in Norway.