﻿THE 
  RED 
  SPIDER 
  ON 
  HOPS 
  IN 
  CALIFORNIA. 
  17 
  

  

  NATURE 
  OF 
  DAMAGE. 
  

   GENERAL 
  EFFECT 
  OF 
  MITES 
  UPON 
  FOLIAGE. 
  

  

  These 
  mites 
  feed 
  upon 
  the 
  juices 
  and 
  cell 
  contents 
  which 
  they 
  

   suck 
  from 
  the 
  tissues 
  of 
  the 
  host 
  plant. 
  This 
  extraction 
  of 
  cell 
  

   contents 
  usually 
  results 
  in 
  the 
  formation 
  of 
  a 
  light 
  spot 
  at 
  the 
  point 
  

   where 
  the 
  mite 
  has 
  fed. 
  The 
  presence 
  of 
  mites 
  upon 
  a 
  vine 
  during 
  

   the 
  early 
  summer 
  is 
  readily 
  detected 
  by 
  these 
  yellow 
  spots 
  in 
  the 
  

   surface 
  of 
  the 
  leaves. 
  As 
  the 
  mites 
  increase 
  in 
  numbers 
  the 
  leaves 
  

   become 
  more 
  "speckled," 
  turn 
  yellowish, 
  and 
  when 
  severely 
  injured 
  

   dry 
  up 
  and 
  fall 
  to 
  the 
  ground. 
  Severely 
  infested 
  vines, 
  at 
  the 
  time 
  

   that 
  the 
  hop 
  cones 
  are 
  forming, 
  were 
  observed 
  to 
  be 
  very 
  yellow 
  and 
  

   to 
  lose 
  many 
  leaves. 
  

  

  The 
  decrease 
  in 
  the 
  vitality 
  of 
  the 
  vine, 
  which 
  is 
  the 
  direct 
  result 
  

   of 
  the 
  attack 
  by 
  mites, 
  produces 
  a 
  premature 
  ripening 
  of 
  the 
  hops. 
  

   The 
  hop 
  cones 
  in 
  infested 
  yards 
  were 
  much 
  further 
  advanced 
  than 
  

   those 
  in 
  uninfested 
  hopyards 
  under 
  similar 
  soil 
  and 
  climatic 
  con- 
  

   ditions. 
  This 
  premature 
  ripening 
  results 
  in 
  a 
  decrease 
  in 
  yield 
  and 
  a 
  

   weakening 
  of 
  the 
  roots, 
  tending 
  to 
  decrease 
  the 
  crop 
  of 
  the 
  following 
  

   year. 
  

  

  RELATIVE 
  EFFECT 
  OF 
  MITES 
  UPON 
  MALE 
  AND 
  FEMALE 
  HOPVINES. 
  

  

  The 
  male 
  vines 
  throughout 
  the 
  season 
  showed 
  more 
  immediate 
  

   and 
  serious 
  injury 
  than 
  the 
  surrounding 
  female 
  vines. 
  In 
  many 
  cases 
  

   they 
  were 
  almost 
  entirely 
  defoliated 
  (PL 
  II, 
  figs. 
  1, 
  2), 
  while 
  the 
  

   neighboring 
  female 
  vines 
  were 
  but 
  slightly 
  injured. 
  

  

  Some 
  leaves 
  which 
  expanded 
  late 
  in 
  the 
  season 
  on 
  the 
  lower 
  parts 
  

   of 
  the 
  pistillate 
  vines 
  were 
  thin 
  and 
  papery, 
  appearing 
  identical 
  in 
  

   texture 
  with 
  the 
  leaves 
  of 
  the 
  male 
  vine, 
  and 
  showed 
  an 
  injury 
  similar 
  

   to 
  that 
  of 
  the 
  male 
  foliage. 
  This 
  severe 
  injury 
  to 
  the 
  male 
  vines 
  

   appears 
  to 
  be 
  due 
  largely 
  to 
  the 
  nature 
  of 
  the 
  foliage 
  and 
  not 
  to 
  the 
  

   presence 
  of 
  a 
  larger 
  number 
  of 
  mites 
  than 
  are 
  found 
  upon 
  the 
  female 
  

   vines. 
  

  

  EFFECT 
  UPON 
  THE 
  QUALITY 
  OF 
  THE 
  HOPS. 
  

  

  Although 
  the 
  foliage 
  upon 
  the 
  arms 
  of 
  the 
  vines 
  was 
  infested 
  at 
  

   the 
  time 
  the 
  hops 
  were 
  coming 
  out 
  of 
  the 
  burr, 
  the 
  mites 
  were 
  not 
  

   observed 
  actually 
  to 
  feed 
  upon 
  them 
  until 
  they 
  were 
  nearly 
  full-sized. 
  

   No 
  direct 
  injury 
  was 
  noted 
  when 
  the 
  mites 
  were 
  first 
  found 
  upon 
  

   the 
  cones, 
  but 
  soon 
  reddish-brown 
  spots 
  appeared 
  upon 
  the 
  scales 
  

   and 
  gradually 
  the 
  natural 
  green 
  and 
  yellow 
  turned 
  to 
  reddish 
  brown, 
  

   the 
  scales 
  became 
  scraggly, 
  and 
  in 
  severe 
  cases 
  the 
  hop 
  cones 
  became 
  

   so 
  brittle 
  that 
  they 
  could 
  not 
  be 
  picked. 
  (See 
  PL 
  V, 
  fig. 
  1.) 
  

  

  