﻿HABITS 
  OF 
  THE 
  LAKVA. 
  

  

  25 
  

  

  As 
  an 
  illustration 
  of 
  how 
  abundant 
  this 
  insect 
  may 
  become, 
  the 
  

   following 
  observations 
  are 
  given: 
  On 
  August 
  31, 
  1909, 
  Mr. 
  Foster, 
  

   of 
  this 
  bureau, 
  found 
  it 
  severely 
  infesting 
  pear 
  foliage 
  at 
  Martinez, 
  

   Cal., 
  and 
  noted 
  as 
  many 
  as 
  200 
  larvae 
  on 
  one 
  side 
  of 
  a 
  leaf. 
  On 
  

   July 
  28, 
  1910, 
  the 
  writer 
  found 
  some 
  plants 
  of 
  spiny 
  lettuce 
  badly 
  

   infested 
  by 
  the 
  larvae 
  of 
  this 
  thrips, 
  and 
  10 
  leaves 
  gave 
  a 
  total 
  infes- 
  

   tation 
  of 
  733. 
  (See 
  Table 
  III.) 
  This 
  gave 
  an 
  average 
  of 
  73.3 
  to 
  each 
  

   leaf. 
  

  

  Table 
  III. 
  — 
  Infestation 
  of 
  Lactuca 
  scariola 
  by 
  larvce 
  of 
  the 
  bean 
  thrips. 
  

  

  No. 
  of 
  

   leaf. 
  

  

  Number 
  

  

  of 
  larvae 
  

  

  on 
  under 
  

  

  side. 
  

  

  Number 
  

  

  of 
  larvae 
  

  

  on 
  upper 
  

  

  side. 
  

  

  Total 
  

  

  number 
  of 
  

  

  larvae 
  

  

  on 
  leaf. 
  

  

  No. 
  of 
  

   leaf. 
  

  

  Number 
  

  

  of 
  larvae 
  

  

  on 
  under 
  

  

  side. 
  

  

  Number 
  

  

  of 
  larvae 
  

  

  on 
  upper 
  

  

  side. 
  

  

  Total 
  

   number 
  

   of 
  larvae 
  

   on 
  leaf. 
  

  

  1 
  

   2 
  

   3 
  

   4 
  

   5 
  

   6 
  

  

  70 
  

   34 
  

   43 
  

   30 
  

   59 
  

   46 
  

  

  7 
  

  

  39 
  

  

  2 
  

  

  2 
  

  

  47 
  

  

  46 
  

  

  77 
  

   73 
  

   45 
  

   32 
  

   106 
  

   92 
  

  

  7 
  

   8 
  

   9 
  

   10 
  

  

  44 
  

   61 
  

   70 
  

   23 
  

  

  47 
  

  

  30 
  

  

  1 
  

  

  32 
  

  

  91 
  

   91 
  

   71 
  

   55 
  

  

  480 
  

  

  253 
  

  

  733 
  

  

  On 
  July 
  18, 
  1911, 
  at 
  Hollywood, 
  Cal., 
  leaves 
  of 
  spiny 
  lettuce 
  were 
  

   found 
  that 
  had 
  several 
  hundred 
  larvae 
  to 
  a 
  leaf. 
  September 
  22, 
  1910, 
  

   Mr. 
  Wildermuth 
  observed 
  a 
  field 
  of 
  cotton 
  at 
  El 
  Centro, 
  Cal., 
  show- 
  

   ing 
  considerable 
  injury 
  by 
  this 
  insect, 
  and 
  counted 
  as 
  many 
  as 
  200 
  

   larvae 
  to 
  a 
  single 
  leaf. 
  

  

  MOLTING. 
  

  

  The 
  larva 
  molts 
  once, 
  giving 
  two 
  larval 
  instars, 
  then 
  molts 
  to 
  the 
  

   prepupal 
  stage. 
  On 
  July 
  28, 
  1910, 
  a 
  number 
  of 
  larvae 
  that 
  had 
  just 
  

   hatched 
  were 
  separated 
  and 
  on 
  August 
  2 
  these 
  all 
  molted. 
  On 
  August 
  

   7 
  they 
  again 
  molted 
  and 
  changed 
  to 
  prepupae. 
  This 
  gave 
  the 
  first 
  

   instar 
  a 
  length 
  of 
  five 
  days 
  and 
  the 
  second 
  a 
  length 
  of 
  five 
  days. 
  The 
  

   process 
  of 
  molting 
  in 
  the 
  larva 
  is 
  continued 
  unprotected 
  in 
  the 
  midst 
  

   of 
  the 
  feeding 
  colony. 
  After 
  molting 
  the 
  skin 
  is 
  left 
  adhering 
  to 
  the 
  

   leaf 
  beside 
  the 
  feeding 
  larva. 
  

  

  It 
  was 
  observed 
  with 
  the 
  larvae 
  of 
  this 
  species 
  and 
  of 
  those 
  of 
  the 
  

   greenhouse 
  thrips 
  that 
  when 
  they 
  were 
  exposed 
  to 
  a 
  low 
  temperature 
  

   the 
  entire 
  development 
  was 
  checked 
  and 
  growth 
  remained 
  stationary 
  

   during 
  the 
  exposure. 
  In 
  long-continued 
  exposures 
  the 
  insects 
  were 
  

   killed, 
  but 
  if 
  within 
  three 
  weeks 
  they 
  were 
  again 
  removed 
  to 
  higher 
  

   temperatures 
  the 
  larvae 
  resumed 
  their 
  growth 
  and 
  pupated 
  in 
  a 
  

   few 
  days. 
  

  

  Under 
  the 
  artificial 
  conditions 
  of 
  rearing 
  in 
  vials 
  the 
  mature 
  

   larva' 
  seek 
  concealment 
  before 
  pupation 
  in 
  curled-up 
  leaves, 
  in 
  all 
  

   kinds 
  of 
  protected 
  places, 
  and 
  if 
  in 
  vials 
  closed 
  with 
  cotton 
  plugs 
  

   they 
  work 
  their 
  way 
  in 
  between 
  the 
  plug 
  and 
  side 
  of 
  the 
  vial. 
  In 
  

   the 
  field, 
  however, 
  the 
  Larvae 
  when 
  full 
  grown 
  desert 
  the 
  plants 
  and 
  

   hide 
  in 
  rubbish 
  and 
  cracks 
  in 
  the 
  ground 
  or 
  beneath 
  clods 
  of 
  earth. 
  

   51097°-Hull. 
  118—12 
  4 
  

  

  