﻿22.— 
  RECENT 
  WORK 
  IN 
  FOREST 
  ENTOMOLOGY. 
  

  

  By 
  C. 
  F. 
  C. 
  Beeson, 
  M.A., 
  F.E.S., 
  Forest 
  Zoologist. 
  

  

  The 
  principal 
  investigations 
  that 
  have 
  been 
  carried 
  out 
  by 
  the 
  Forest 
  

   Research 
  Institute 
  during 
  the 
  past 
  two 
  years 
  are 
  studies 
  in 
  the 
  ecology 
  

   of 
  the 
  borer 
  fauna 
  of 
  (a) 
  the 
  sal 
  (Shorea 
  rohusta) 
  and 
  of 
  the 
  trees 
  associated 
  

   with 
  it 
  in 
  sal 
  forests 
  ; 
  and 
  (b) 
  the 
  teak 
  {Tectona 
  grandis) 
  and 
  of 
  some 
  

   of 
  its 
  associates. 
  The 
  method 
  of 
  inquiry 
  comprises 
  (1) 
  prolonged 
  tours 
  

   in 
  the 
  forests 
  to 
  study 
  the 
  seasonal 
  occurrence, 
  distribution 
  and 
  environ- 
  

   mental 
  conditions 
  of 
  the 
  principal 
  species 
  ; 
  and 
  (2) 
  insectary 
  rearing 
  

   experiments. 
  Material 
  for 
  the 
  latter 
  is 
  obtained 
  on 
  tours 
  by 
  despatching 
  

   logs 
  of 
  trees 
  dead 
  from 
  natural 
  causes 
  or 
  from 
  fellings. 
  In 
  addition 
  

   material 
  is 
  obtained 
  from 
  timber-seasoning 
  depots 
  throughout 
  India, 
  

   as 
  experiments 
  are 
  now 
  in 
  progress 
  in 
  methods 
  of 
  natural 
  seasoning 
  

   that 
  are 
  being 
  carried 
  out 
  in 
  co-operation 
  with 
  the 
  section 
  of 
  Forest 
  

   Economics. 
  Hundreds 
  of 
  logs 
  of 
  various 
  tree 
  species 
  pass 
  through 
  the 
  

   insectary 
  at 
  Delira 
  Dun. 
  Illustrations 
  of 
  the 
  breeding 
  cages 
  used 
  are 
  

   given 
  in 
  the 
  Report 
  of 
  the 
  Third 
  Entomological 
  Meeting. 
  

  

  (a) 
  Sal 
  Borers. 
  The 
  more 
  important 
  borers 
  are 
  Ho'ploceramhyx 
  

   spinicornis, 
  Molesthes 
  holosericea 
  and 
  species 
  of 
  Platypodidae. 
  The 
  

   former 
  of 
  these 
  has 
  occurred 
  in 
  epidemic 
  incidence 
  as 
  a 
  primary 
  pest 
  

   killing 
  living 
  sal 
  trees 
  ; 
  normally 
  it 
  is 
  a 
  borer 
  of 
  felled 
  or 
  killed 
  timber. 
  

   An 
  account 
  of 
  epidemic 
  is 
  given 
  in 
  an 
  article 
  in 
  the 
  Indian 
  Forester, 
  

   February 
  1921. 
  [This 
  was 
  described 
  to 
  the 
  Meeting 
  illustrated 
  by 
  dia- 
  

   grams]. 
  It 
  has 
  been 
  found 
  that 
  sal 
  trees 
  are 
  killed 
  by 
  mass-attack 
  in 
  

   years 
  of 
  exceptionally 
  heavy 
  rainfall. 
  In 
  years 
  of 
  rainfall 
  below 
  the 
  

   average 
  the 
  mortality 
  is 
  less 
  owing, 
  on 
  the 
  one 
  hand, 
  to 
  the 
  increased 
  

   power 
  of 
  resistence 
  of 
  the 
  tree 
  due 
  to 
  better 
  soil-aeration 
  and 
  on 
  the 
  

   other 
  to 
  climatic 
  reduction 
  in 
  the 
  incidence 
  of 
  the 
  beetle. 
  The 
  correla- 
  

   tion 
  of 
  rainfall 
  and 
  mortality 
  of 
  trees 
  is 
  very 
  striking. 
  The 
  effect 
  of 
  

   rainfall 
  (as 
  expressed 
  in 
  terms 
  of 
  the 
  water-content 
  of 
  the 
  heartwood 
  of 
  

   sal) 
  on 
  the 
  metabolism 
  of 
  the 
  pupal 
  and 
  early 
  larval 
  stages 
  has 
  been 
  

   studied 
  and 
  it 
  has 
  been 
  found 
  that 
  the 
  incidence 
  of 
  emergence 
  of 
  the 
  

   beetle 
  synchronises 
  with 
  the 
  incidence 
  of 
  rainfall 
  in 
  the 
  first 
  few 
  weeks 
  

   of 
  the 
  monsoon. 
  In 
  a 
  wet 
  year 
  75 
  per 
  cent, 
  of 
  the 
  beetles 
  emerge 
  in 
  

   the 
  first 
  month 
  of 
  the 
  rains 
  ; 
  in 
  a 
  dry 
  year 
  this 
  period 
  is 
  prolonged 
  to 
  six 
  

   to 
  eight 
  weeks. 
  Control 
  measures 
  have 
  been 
  devised 
  from 
  the 
  results 
  of 
  

   these 
  investigations. 
  Similar 
  .work 
  on 
  the 
  emergence 
  periods 
  is 
  being 
  

   done 
  with 
  other 
  species 
  of 
  borers. 
  It 
  is 
  believed 
  that 
  control 
  of 
  borers 
  of 
  

  

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  ) 
  

  

  