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  THE 
  BEAN 
  THRIPS. 
  

  

  marked 
  by 
  feeding 
  of 
  some 
  thrips 
  furnishes 
  good 
  evidence 
  that 
  the 
  

   bean 
  thrips 
  has 
  been 
  feeding 
  there 
  at 
  some 
  time. 
  The 
  larvae 
  feed 
  in 
  

   much 
  the 
  same 
  manner 
  as 
  the 
  adult, 
  the 
  mouthparts 
  being 
  practically 
  

   the 
  same. 
  They 
  gradually 
  scrape 
  out 
  the 
  contents 
  of 
  the 
  leaf, 
  leav- 
  

   ing 
  silvery 
  spots, 
  which 
  as 
  they 
  become 
  abundant 
  often 
  unite 
  and 
  

   gradually 
  destroy 
  the 
  vitality 
  of 
  the 
  leaf. 
  Most 
  of 
  the 
  eggs 
  seem 
  to 
  

   be 
  laid 
  on 
  the 
  underside 
  of 
  the 
  leaves, 
  although 
  the 
  writer 
  has 
  ob- 
  

   served 
  eggs 
  to 
  hatch 
  from 
  the 
  upper 
  side 
  also. 
  As 
  a 
  consequence 
  

   the 
  larvae 
  begin 
  feeding 
  largely 
  on 
  the 
  underside 
  of 
  the 
  leaves. 
  After 
  

   hatching 
  they 
  do 
  not 
  move 
  far 
  before 
  commencing 
  to 
  feed, 
  during 
  

   which 
  time, 
  under 
  ordinary 
  conditions, 
  they 
  move 
  very 
  little. 
  When 
  

   plants 
  are 
  first 
  infested 
  the 
  larvae 
  seem 
  to 
  feed 
  close 
  to 
  the 
  leaf 
  

   veins, 
  but 
  as 
  they 
  become 
  more 
  abundant 
  they 
  scatter 
  in 
  groups 
  over 
  

   the 
  entire 
  leaf 
  surface. 
  Like 
  those 
  of 
  the 
  greenhouse 
  thrips 
  the 
  

   larvae 
  of 
  this 
  species 
  seem 
  to 
  cluster 
  in 
  colonies 
  and 
  unless 
  disturbed, 
  

   or 
  in 
  need 
  of 
  fresh 
  food, 
  remain 
  thus. 
  The 
  colonies 
  are 
  in 
  many 
  cases 
  

   found 
  in 
  between 
  two 
  veins 
  of 
  the 
  leaves. 
  When 
  disturbed 
  the 
  larvae 
  

   will 
  violently 
  twitch 
  the 
  end 
  of 
  the 
  abdomen 
  with 
  its 
  drop 
  of 
  liquid 
  

   and 
  move 
  away 
  rapidly. 
  Apparently 
  this 
  is 
  used 
  as 
  a 
  means 
  of 
  de- 
  

   fense, 
  for 
  the 
  writer, 
  in 
  work 
  with 
  a 
  parasite 
  of 
  this 
  thrips, 
  observed 
  

   at 
  times 
  that 
  these 
  larvae 
  when 
  touched 
  from 
  in 
  front 
  by 
  the 
  parasite 
  

   flung 
  the 
  abdomen 
  around 
  and 
  moved 
  rapidly 
  away. 
  When 
  this 
  oc- 
  

   curred 
  the 
  parasite 
  generally 
  retreated, 
  but 
  returned 
  to 
  the 
  attack 
  

   and 
  later 
  usually 
  succeeded 
  in 
  ovipositing 
  in 
  its 
  host. 
  

  

  The 
  larvae 
  and 
  adults 
  of 
  this 
  thrips 
  feed 
  together 
  in 
  colonies, 
  and 
  

   as 
  the 
  leaves 
  become 
  crowded 
  or 
  dry 
  from 
  excessive 
  feeding 
  the 
  

   larvae 
  move 
  in 
  search 
  of 
  fresh 
  food. 
  Gradually 
  the 
  whole 
  under- 
  

   side 
  of 
  the 
  leaf 
  attacked 
  becomes 
  infested 
  by 
  the 
  larvae 
  and 
  then 
  

   the 
  surface 
  as 
  well. 
  In 
  fact, 
  the 
  writer 
  has 
  seen 
  leaves 
  so 
  heavily 
  

   infested 
  by 
  the 
  larvae 
  of 
  this 
  thrips 
  as 
  to 
  give 
  them 
  a 
  decidedly 
  

   larvae 
  move 
  in 
  search 
  of 
  fresh 
  food 
  food. 
  Gradually 
  the 
  whole 
  under 
  

   reddish 
  color, 
  due 
  to 
  the 
  bodies 
  of 
  the 
  insects. 
  So 
  far 
  this 
  larva 
  

   has 
  not 
  been 
  observed 
  feeding 
  in 
  the 
  blossoms 
  of 
  any 
  plant, 
  

   but 
  in 
  some 
  cases 
  it 
  has 
  been 
  observed 
  feeding 
  on 
  green 
  tomatoes, 
  

   and 
  when 
  bean 
  vines 
  are 
  badly 
  infested 
  the 
  pods 
  are 
  also 
  attacked. 
  

   Indeed, 
  when 
  excessively 
  abundant, 
  these 
  insects 
  will 
  not 
  only 
  

   cover 
  both 
  sides 
  of 
  the 
  leaves^ 
  but 
  the 
  stem 
  of 
  the 
  plant 
  as 
  well. 
  

   The 
  larvae 
  as 
  a 
  rule 
  feed 
  unprotected 
  on 
  the 
  leaf, 
  but 
  at 
  times 
  may 
  

   be 
  found 
  feeding 
  under 
  the 
  protection 
  of 
  red-spider 
  webs. 
  

  

  Apparently 
  these 
  minute 
  creatures 
  are 
  not 
  affected 
  by 
  dust, 
  as 
  

   the 
  writer 
  has 
  found 
  them 
  feeding 
  in 
  large 
  numbers 
  on 
  leaves 
  of 
  

   spiny 
  lettuce 
  in 
  an 
  alley 
  in 
  the 
  city 
  of 
  Los 
  Angeles 
  when 
  the 
  leaves 
  

   were 
  so 
  thickly 
  covered 
  with 
  dust 
  as 
  completely 
  to 
  hide 
  the 
  surface. 
  

   It 
  would 
  seem 
  that 
  with 
  the 
  enormous 
  clouds 
  of 
  dust 
  that 
  arise 
  in 
  

   this 
  section 
  during 
  the 
  entire 
  summer, 
  completely 
  coating 
  the 
  larvae, 
  

   they 
  would 
  speedily 
  succumb. 
  

  

  