﻿10 
  

  

  THE 
  EED 
  SPIDER 
  ON 
  HOPS 
  IN 
  CALIFORNIA. 
  

  

  An 
  extract 
  from 
  a 
  letter 
  from 
  a 
  former 
  hop 
  grower 
  in 
  Washington 
  

   State 
  describes 
  conditions 
  there 
  as 
  follows: 
  "The 
  'red 
  spider' 
  was 
  

   here 
  in 
  1901 
  , 
  but 
  did 
  little 
  damage. 
  It 
  gradually 
  increased 
  until 
  1905, 
  

   when 
  we 
  let 
  25 
  of 
  85 
  acres 
  blow 
  away 
  and 
  what 
  we 
  did 
  bale 
  was 
  

   trash. 
  Then 
  we 
  gave 
  up 
  the 
  fight." 
  

  

  The 
  red 
  spider 
  is 
  reported 
  to 
  have 
  been 
  very 
  destructive 
  to 
  hops 
  

   at 
  Agassiz, 
  British 
  Columbia, 
  but 
  for 
  the 
  past 
  few 
  years 
  has 
  not 
  ap- 
  

   peared 
  in 
  injurious 
  numbers. 
  

  

  The 
  past 
  seasons 
  were 
  very 
  late, 
  and 
  the 
  mites 
  were 
  not 
  present 
  in 
  

   noticeable 
  numbers 
  in 
  the 
  hop 
  fields 
  near 
  Sacramento 
  until 
  the 
  middle 
  

   of 
  June. 
  Even 
  so, 
  they 
  had 
  done 
  much 
  damage 
  by 
  August, 
  1911, 
  

   and 
  if 
  the 
  crop 
  had 
  not 
  been 
  promptly 
  and 
  rapidly 
  picked 
  many 
  of 
  the 
  

  

  hops 
  would 
  have 
  "blown 
  away," 
  

   resulting 
  in 
  the 
  total 
  loss 
  of 
  a 
  

   great 
  portion 
  of 
  the 
  crop. 
  

  

  LIFE 
  HISTORY. 
  

  

  THE 
  EGG. 
  

  

  Description. 
  — 
  The 
  eggs 
  of 
  

   TetranycJius 
  bimaculatus 
  (fig. 
  1) 
  

   are 
  small, 
  spherical, 
  pearl-like 
  

   objects, 
  about 
  one-sixth 
  of 
  a 
  

   millimeter 
  in 
  diameter, 
  though 
  

   somewhat 
  variable 
  in 
  size. 
  

  

  FiG.l. 
  — 
  The 
  red 
  spider 
  ( 
  Tetranychus 
  bimaculatus): 
  Egg 
  

   (position 
  indicated 
  by 
  white 
  circle) 
  among 
  webs 
  on 
  

   surface 
  of 
  leaves. 
  Greatly 
  enlarged. 
  (Original.) 
  

  

  From 
  10 
  to 
  450 
  are 
  usually 
  present 
  on 
  a 
  leaf, 
  and 
  with 
  the 
  aid 
  of 
  a 
  

   hand 
  lens 
  they 
  are 
  readily 
  found 
  upon 
  infested 
  foliage. 
  

  

  Where 
  laid. 
  — 
  The 
  eggs 
  are 
  deposited 
  singly 
  and 
  are 
  promiscuously 
  

   distributed 
  among 
  the 
  webs 
  and 
  upon 
  the 
  underside 
  of 
  the 
  leaves. 
  

   They 
  are 
  not 
  attached 
  to 
  the 
  host 
  plant 
  by 
  protecting 
  webs, 
  as 
  are 
  

   the 
  eggs 
  of 
  the 
  citrus 
  "red 
  spider" 
  {Tetranychus 
  mytilaspidis 
  Riley), 
  

   but 
  are 
  held 
  by 
  strong 
  filaments 
  with 
  which 
  they 
  chance 
  to 
  come 
  in 
  

   contact. 
  Many 
  eggs 
  have 
  been 
  observed 
  on 
  the 
  loose 
  "web 
  which 
  is 
  

   ordinarily 
  spun 
  over 
  infested 
  leaves. 
  

  

  Incubation. 
  — 
  The 
  incubation 
  period 
  varies 
  according 
  to 
  temperature 
  

   and 
  general 
  climatic 
  conditions. 
  In 
  the 
  experiments 
  conducted 
  at 
  

   Berkeley, 
  CaL, 
  during 
  February, 
  1912, 
  the 
  incubation 
  period 
  was 
  

   found 
  to 
  be 
  from 
  8 
  to 
  10 
  days. 
  This 
  period 
  during 
  May 
  was 
  from 
  5 
  

   to 
  10 
  days, 
  with 
  an 
  average 
  of 
  7.2 
  days, 
  while 
  in 
  July, 
  1911, 
  and 
  during 
  

   some 
  very 
  warm 
  weather 
  in 
  1912 
  it 
  was 
  only 
  4^ 
  days. 
  The 
  relatively 
  

   higher 
  temperatures 
  of 
  the 
  summer 
  are 
  responsible 
  for 
  this 
  shortening. 
  

  

  