﻿SEASONAL 
  HISTORY 
  IN 
  THE 
  IMPERIAL 
  VALLEY. 
  37 
  

  

  tion. 
  The 
  larvae 
  become 
  much 
  less 
  numerous 
  and 
  require 
  an 
  extended 
  

   period 
  to 
  complete 
  their 
  growth. 
  In 
  1910 
  the 
  last 
  larva? 
  in 
  numbers 
  

   were 
  observed 
  in 
  the 
  field 
  on 
  November 
  20, 
  while 
  one 
  was 
  observed 
  on 
  

   December 
  1, 
  and 
  three 
  on 
  December 
  13, 
  and 
  during 
  the 
  first 
  part 
  of 
  

   December 
  these 
  had 
  all 
  changed 
  to 
  pupae 
  or 
  died. 
  The 
  last 
  adult 
  

   appeared 
  on 
  December 
  27. 
  In 
  1911 
  the 
  larvae 
  were 
  not 
  very 
  abundant 
  

   after 
  the 
  first 
  week 
  in 
  October, 
  and 
  the 
  last 
  ones 
  were 
  observed 
  in 
  

   Los 
  Angeles 
  County 
  on 
  November 
  21. 
  

  

  NUMBER 
  OF 
  GENERATIONS. 
  

  

  In 
  the 
  section 
  of 
  the 
  State 
  in 
  which 
  this 
  insect 
  was 
  under 
  observa- 
  

   tion, 
  the 
  first 
  spring 
  generation 
  may 
  commence 
  as 
  early 
  as 
  January 
  

   10 
  and 
  probably 
  egg-laying 
  by 
  overwintering 
  adults 
  continues 
  for 
  a 
  

   considerable 
  time. 
  As 
  the 
  period 
  of 
  oviposition 
  is 
  quite 
  extended 
  the 
  

   different 
  broods 
  tend 
  to 
  overlap 
  ; 
  still 
  in 
  midsummer 
  there 
  are 
  certain 
  

   periods 
  when 
  the 
  majority 
  of 
  thrips 
  present 
  may 
  be 
  adults 
  or 
  larvae. 
  

   Up 
  to 
  April 
  1 
  there 
  is 
  probably 
  one 
  small 
  full 
  generation 
  occupying 
  

   about 
  56 
  days. 
  During 
  April 
  and 
  May 
  a 
  second 
  generation 
  will 
  

   develop; 
  then 
  during 
  the 
  four 
  months 
  of 
  June, 
  July, 
  August, 
  and 
  

   September 
  there 
  is 
  one 
  full 
  generation 
  for 
  each 
  month. 
  For 
  the 
  rest 
  

   of 
  the 
  period 
  of 
  the 
  breeding 
  activity 
  we 
  have 
  probably 
  a 
  partial 
  

   brood 
  that 
  extends 
  over 
  68 
  to 
  73 
  days. 
  

  

  Thus 
  during 
  the 
  year 
  this 
  insect 
  has 
  a 
  small 
  generation 
  in 
  both 
  the 
  

   early 
  spring 
  and 
  late 
  fall 
  and 
  five 
  full 
  generations 
  during 
  the 
  rest 
  of 
  

   the 
  time, 
  or 
  seven 
  generations 
  a 
  year. 
  

  

  SEASONAL 
  HISTORY 
  IN 
  THE 
  IMPERIAL 
  VALLEY. 
  

  

  The 
  observations 
  on 
  the 
  life 
  cycle 
  of 
  this 
  insect 
  for 
  Imperial 
  Valley 
  

   were 
  conducted 
  by 
  Mr. 
  V. 
  L. 
  Wildermuth 
  at 
  El 
  Centro, 
  Cal., 
  in 
  1910. 
  

  

  BGG 
  PERIOD. 
  

  

  Mr. 
  Wildermuth 
  confined 
  adults 
  in 
  vials 
  with 
  fresh 
  sprigs 
  of 
  

   alfalfa 
  and 
  kept 
  the 
  foliage 
  fresh 
  by 
  wrapping 
  the 
  stems 
  in 
  moist 
  

   cotton 
  until 
  the 
  larvae 
  hatched 
  from 
  the 
  eggs. 
  While 
  many 
  eggs 
  were 
  

   secured 
  by 
  this 
  method, 
  large 
  numbers 
  died 
  before 
  hatching, 
  as 
  the 
  

   foliage 
  became 
  too 
  dry. 
  but, 
  as 
  shown 
  in 
  Table 
  XI, 
  the 
  egg 
  stage 
  

   \ 
  a 
  ried 
  from 
  four 
  days 
  in 
  a 
  single 
  case 
  to 
  five 
  days 
  in 
  a 
  lot 
  of 
  20 
  eggs 
  

   laid 
  the 
  last 
  day 
  of 
  August. 
  The 
  length 
  of 
  the 
  egg 
  stage 
  at 
  that 
  

   locality 
  was 
  only 
  one-third 
  as 
  great 
  as 
  (hat 
  observed 
  by 
  the 
  writer 
  in 
  

   Los 
  Angeles 
  County, 
  but 
  this 
  is 
  due 
  in 
  a 
  large 
  measure 
  to 
  the 
  high 
  

   temperature 
  of 
  the 
  Imperial 
  Valley. 
  

  

  