﻿THE 
  USE 
  OF 
  EXPERIMENTAL 
  PLOTS 
  AND 
  FOREST 
  INSECTS. 
  

  

  159 
  

  

  and 
  in 
  10% 
  they 
  had 
  in 
  vain 
  attempted 
  to 
  enter. 
  The 
  supposition 
  at 
  once 
  presents 
  

   itself 
  that 
  the 
  primary 
  cause 
  of 
  the 
  attack 
  of 
  the 
  pine-beetle 
  was 
  the 
  defoliation 
  

   brought 
  about 
  by 
  Bupalus 
  piniarius, 
  which 
  had 
  weakened 
  the 
  trees 
  to 
  such 
  an 
  

   extent 
  as 
  to 
  render 
  them 
  appetising 
  to 
  the 
  beetles. 
  A 
  closer 
  examinations 
  of 
  the 
  

   trees 
  on 
  the 
  experimental 
  plot 
  showed, 
  however, 
  that 
  this 
  cannot 
  be 
  the 
  case 
  in 
  

   this 
  instance, 
  at 
  least 
  not 
  to 
  any 
  great 
  extent. 
  

  

  According 
  to 
  the 
  estimates 
  made 
  in 
  1917, 
  71 
  of 
  the 
  126 
  trees 
  of 
  the 
  plot 
  had 
  an 
  

   average 
  injury, 
  14 
  being 
  severely 
  defoliated 
  and 
  the 
  rest 
  having 
  escaped 
  any 
  visible 
  

   damage. 
  Only 
  one 
  of 
  the 
  14 
  severely 
  injured 
  trees 
  had 
  in 
  the 
  spring 
  of 
  1918 
  been 
  

   attacked 
  by 
  the 
  pine-beetle, 
  and 
  that 
  in 
  vain. 
  Moreover, 
  we 
  notice 
  that 
  one 
  of 
  the 
  

   trees 
  in 
  which 
  the 
  pine-beetle 
  was 
  breeding 
  had 
  not 
  previously 
  been 
  attacked 
  by 
  

   Bupalus, 
  nor 
  had 
  five 
  other 
  trees 
  into 
  which 
  the 
  beetle 
  had 
  in 
  vain 
  tried 
  to 
  enter 
  

   been 
  previously 
  injured 
  by 
  the 
  moth. 
  Fig. 
  2 
  shows 
  how 
  the 
  attacks 
  of 
  the 
  moth. 
  

  

  Fig. 
  2. 
  Diagram 
  showing 
  the 
  distribution 
  of 
  attacks 
  of 
  

   Bupalus 
  piniarius 
  (solid 
  line) 
  and 
  the 
  pine 
  beetle 
  (dotted 
  line) 
  

   on 
  trees 
  of 
  different 
  dimensions. 
  

  

  and 
  beetle 
  are 
  distributed 
  in 
  trees 
  of 
  different 
  dimensions, 
  from 
  which 
  it 
  is 
  evident 
  

   how 
  little 
  the 
  attack 
  of 
  the 
  pine-beetle 
  is 
  connected 
  with 
  that 
  of 
  Bupalus. 
  We 
  

   notice 
  that 
  only 
  24% 
  of 
  the 
  trees 
  measuring 
  less 
  than 
  15 
  cm. 
  at 
  breast 
  height 
  have 
  

   suffered 
  from 
  the 
  moth, 
  whereas 
  all 
  trees 
  measuring 
  more 
  than 
  30 
  cm. 
  have 
  been, 
  

   attacked. 
  The 
  pine-beetle, 
  on 
  the 
  other 
  hand 
  has 
  preferred 
  the 
  smaller 
  trees, 
  

   those 
  exceeding 
  30 
  cm. 
  not 
  being 
  attacked 
  at 
  all. 
  

  

  From 
  this 
  it 
  is 
  evident 
  that 
  the 
  two 
  insects, 
  the 
  pine-tree 
  looper 
  and 
  the 
  pine- 
  

   beetle, 
  work 
  on 
  two 
  different 
  lines, 
  one 
  selecting 
  the 
  largest 
  trees, 
  the 
  other 
  

   preferring 
  the 
  smaller 
  ones. 
  The 
  investigation 
  has 
  also 
  revealed 
  the 
  fact 
  that 
  

   during 
  the 
  outbreak 
  in 
  1916-1917 
  the 
  forest 
  was 
  able 
  to 
  withstand 
  the 
  defoliation 
  

   and 
  that 
  the 
  subsequent 
  attack 
  of 
  the 
  pine-beetles 
  was 
  in 
  no 
  way 
  the 
  consequence 
  

   of 
  the 
  previous 
  defoliation, 
  but 
  would 
  have 
  happened 
  in 
  any 
  case. 
  

   (C605) 
  F 
  

  

  