﻿158 
  IV 
  AR 
  TRAGARDH. 
  

  

  We 
  find 
  in 
  the 
  literature 
  regarding 
  Bupalus 
  piniarius 
  the 
  statement 
  that 
  the 
  

   trees 
  are 
  able 
  to 
  withstand 
  a 
  defoliation, 
  provided 
  it 
  is 
  not 
  repeated 
  and 
  does 
  not 
  

   occur 
  early 
  in 
  the 
  autumn. 
  If, 
  on 
  the 
  other 
  hand, 
  the 
  defoliation 
  is 
  repeated 
  during 
  

   two 
  years 
  in 
  succession 
  the 
  trees 
  are 
  said 
  to 
  be 
  past 
  recovery. 
  As 
  this 
  conclusion 
  

   was 
  based 
  on 
  observations 
  made 
  chiefly 
  in 
  Germany 
  and 
  as 
  it 
  did 
  not 
  seem 
  safe 
  

   to 
  assume 
  its 
  applicability 
  in 
  Sweden, 
  investigations 
  on 
  the 
  state 
  of 
  health 
  of 
  pine- 
  

   trees 
  after 
  a 
  defoliation 
  repeated 
  during 
  two 
  years 
  were 
  carried 
  on 
  in 
  1917 
  and 
  1918. 
  

  

  At 
  Sorby 
  in 
  Sodermanland 
  the 
  degree 
  of 
  infestation 
  in 
  May 
  1917 
  was 
  found 
  to 
  be 
  

   97*8 
  pupae 
  per 
  square 
  metre, 
  18 
  per 
  cent, 
  of 
  which 
  were 
  parasitised. 
  By 
  counting 
  

   the 
  needles 
  it 
  was 
  found 
  that 
  the 
  average 
  defoliation 
  at 
  the 
  top 
  of 
  the 
  trees 
  was 
  

   75%, 
  the 
  injury 
  decreasing 
  gradually 
  downwards, 
  so 
  that 
  in 
  the 
  lower 
  part 
  of 
  the 
  

   crown 
  about 
  60% 
  of 
  the 
  needles 
  were 
  intact. 
  

  

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  Fig. 
  1. 
  Map 
  of 
  experimental 
  plot 
  in 
  pine 
  forest 
  attacked 
  by 
  Bupalus 
  piniarius, 
  

   L., 
  at 
  Sorby, 
  Sweden 
  ; 
  = 
  felled 
  trees, 
  I 
  = 
  average 
  defoliation, 
  II 
  = 
  severe 
  

   defoliation, 
  — 
  = 
  attack 
  by 
  the 
  pine 
  beetle. 
  

  

  At 
  the 
  same 
  time 
  an 
  experimental 
  plot 
  was 
  laid 
  out 
  in 
  the 
  part 
  of 
  the 
  forest 
  most 
  

   seriously 
  injured. 
  In 
  this 
  plot 
  the 
  trees 
  were 
  marked 
  with 
  numbers 
  ; 
  their 
  height, 
  

   diameter 
  at 
  breast 
  height, 
  and 
  the 
  distances 
  between 
  them 
  were 
  measured 
  ; 
  and 
  a 
  

   map 
  was 
  drawn 
  (fig. 
  1), 
  the 
  scale 
  used 
  for 
  the 
  plot 
  being 
  1 
  : 
  100 
  and 
  for 
  the 
  trees 
  

   1 
  : 
  400. 
  Further, 
  the 
  degree 
  of 
  defoliation 
  of 
  each 
  tree 
  was 
  recorded, 
  only 
  three 
  

   degrees 
  being 
  distinguished, 
  viz., 
  no 
  injury, 
  average 
  injury, 
  severe 
  injury. 
  The 
  

   plot 
  was 
  re-examined 
  in 
  May 
  1918, 
  when 
  also 
  the 
  degree 
  of 
  infestation 
  was 
  ascer- 
  

   tained, 
  the 
  number 
  of 
  pupae 
  being 
  found 
  to 
  have 
  been 
  then 
  reduced 
  to 
  8*8 
  per 
  square 
  

   metre, 
  60% 
  of 
  which 
  were 
  parasitised. 
  

  

  The 
  examination 
  made 
  in 
  1918 
  revealed 
  the 
  fact 
  — 
  as 
  astonishing 
  as 
  it 
  was 
  

   satisfactory 
  — 
  that 
  in 
  spite 
  of 
  the 
  attacks 
  during 
  the 
  two 
  previous 
  years 
  not 
  a 
  single 
  

   tree 
  had 
  yet 
  succumbed. 
  In 
  4% 
  of 
  the 
  trees, 
  however, 
  pine-beetles 
  were 
  breeding 
  

  

  