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  661 
  

  

  plant 
  on 
  which 
  they 
  were 
  produced, 
  and 
  when 
  the 
  top 
  of 
  the 
  cover 
  

   was 
  open 
  they 
  immediately 
  took 
  flight, 
  and 
  it 
  would 
  thus 
  appear 
  that 
  

   the 
  winged 
  females 
  demand 
  a 
  change 
  of 
  host 
  plant. 
  The 
  cause 
  of 
  

   this 
  desire 
  to 
  migrate 
  is 
  not 
  clear. 
  It 
  may 
  be 
  due 
  to 
  a 
  simple 
  instinct 
  

   or 
  to 
  a 
  change 
  in 
  the 
  constitution 
  of 
  the 
  cell-sap 
  of 
  the 
  host 
  plant 
  on 
  

   which 
  the 
  aphids 
  feed 
  having 
  an 
  influence 
  on 
  the 
  production 
  of 
  winged 
  

   forms 
  and 
  the 
  consequent 
  migration 
  of 
  the 
  aphids 
  of 
  the 
  original 
  host 
  

   plant. 
  The 
  author 
  considers 
  it 
  not 
  improbable 
  that 
  in 
  the 
  case 
  of 
  

   small 
  plants 
  heavily 
  infested 
  with 
  aphids, 
  the 
  cell-sap 
  may 
  be 
  rendered 
  

   toxic, 
  or 
  at 
  any 
  rate 
  distasteful 
  to 
  the 
  insects. 
  On 
  heavily 
  infested 
  

   plants 
  the 
  aphids 
  became 
  smaller 
  and 
  apparently 
  derived 
  no 
  nourish- 
  

   ment 
  from 
  the 
  host. 
  The 
  actual 
  structure 
  of 
  the 
  pharynx 
  of 
  the 
  

   aphis 
  and 
  the 
  manner 
  in 
  which 
  the 
  food 
  passes 
  into 
  its 
  body 
  is 
  said 
  to 
  

   be 
  such 
  that 
  changes 
  in 
  the 
  surface 
  tension 
  of 
  the 
  cell 
  sap 
  may 
  

   profoundly 
  affect 
  their 
  capacity 
  for 
  feeding. 
  Theobald 
  has 
  

   recorded 
  the 
  migration 
  of 
  Aphis 
  rumicis 
  in 
  the 
  South 
  of 
  England 
  

   in 
  1911. 
  Poppies 
  became 
  heavily 
  infested 
  and 
  subsequently 
  

   masses 
  of 
  winged 
  migrants 
  were 
  distributed 
  over 
  many 
  different 
  

   plants, 
  but 
  only 
  flourished 
  to 
  any 
  great 
  extent 
  on 
  dahhas, 
  beet 
  and 
  

   mangolds. 
  

  

  Those 
  interested 
  in 
  this 
  subject 
  should 
  consult 
  the 
  original 
  paper. 
  

  

  MuNRO 
  (J. 
  W.). 
  A 
  Braconid 
  Parasite 
  on 
  the 
  Pine 
  Weevil 
  (Hylohius 
  

   abietis). 
  — 
  Ann. 
  App. 
  Biol., 
  Cambridge 
  Univ. 
  Press, 
  i, 
  no. 
  2, 
  July 
  

   1914, 
  pp. 
  170-176, 
  4 
  figs. 
  

  

  Near 
  Aberdeen 
  the 
  stamps 
  and 
  roots 
  of 
  Scots 
  Pine 
  which 
  had 
  been 
  

   left 
  on 
  the 
  ground 
  occupied 
  by 
  the 
  existing 
  plantations 
  contained 
  

   large 
  numbers 
  of 
  Hylurgus 
  piniperda 
  and 
  Hylohius 
  abietis. 
  In 
  July 
  

   1913 
  several 
  weevil 
  larvae 
  were 
  found, 
  apparently 
  in 
  the 
  resting 
  

   stage, 
  but 
  attacked 
  by 
  a 
  small 
  legless 
  maggot 
  feeding 
  externally 
  on 
  

   them 
  and 
  sucking 
  their 
  juices. 
  These 
  larvae 
  when 
  supplied 
  with 
  fresh 
  

   grubs 
  fed 
  on 
  them 
  readily, 
  crawling 
  2 
  or 
  3 
  inches 
  to 
  reach 
  their 
  prey. 
  

   Observations 
  showed 
  that 
  they 
  fed 
  through 
  the 
  skin 
  of 
  their 
  host 
  

   and 
  were 
  purely 
  external 
  parasites. 
  They 
  ceased 
  feeding 
  in 
  September, 
  

   moulted 
  a 
  few 
  days 
  later, 
  and 
  on 
  September 
  25th 
  began 
  to 
  spin 
  cocoons. 
  

   On 
  20th 
  February 
  1914, 
  there 
  were 
  pupae 
  in 
  two 
  out 
  of 
  five 
  cocoons 
  

   and 
  nine 
  days 
  later 
  the 
  first 
  imago 
  appeared, 
  others 
  continuing 
  to 
  

   emerge 
  up 
  to 
  and 
  after 
  April 
  14th. 
  The 
  perfect 
  insect 
  was 
  recognised 
  

   as 
  a 
  Braconid 
  agreeing 
  very 
  closely 
  with 
  Ratzeburg's 
  description 
  of 
  

   Bracon 
  hylobii, 
  and, 
  if 
  they 
  are 
  this 
  species, 
  they 
  are 
  new 
  to 
  Britain. 
  

   The 
  degree 
  of 
  parasitism 
  is 
  estimated 
  in 
  the 
  3rd 
  and 
  4th 
  years 
  of 
  the 
  

   appearance 
  of 
  the 
  pest 
  at 
  over 
  30 
  per 
  cent., 
  and 
  the 
  parasite 
  may 
  prove 
  

   of 
  considerable 
  value 
  in 
  combating 
  the 
  pine 
  weevil, 
  which 
  is 
  becoming 
  

   more 
  common 
  every 
  year 
  in 
  new 
  plantations, 
  especially 
  in 
  Scotland. 
  

   The 
  parasite 
  is 
  easily 
  reared 
  and 
  is 
  apparently 
  hardy. 
  The 
  specimens 
  

   were 
  obtained 
  on 
  a 
  bleak 
  hillside 
  near 
  the 
  coast 
  and 
  over 
  600 
  feet 
  

   above 
  sea-level, 
  swept 
  by 
  cold 
  north 
  and 
  east 
  winds. 
  From 
  70 
  cocoons 
  

   no 
  hyperparasites 
  were 
  obtained. 
  The 
  fact 
  that 
  Bracon 
  hylobii 
  attacks 
  

   the 
  weevil 
  larva 
  in 
  its 
  resting 
  stage 
  is 
  interesting, 
  as 
  is 
  also 
  the 
  great 
  

   increase 
  in 
  the 
  numbers 
  of 
  parasites 
  as 
  compared 
  with 
  those 
  of 
  the 
  

   weevil. 
  

  

  