﻿12 
  

  

  THE 
  RED 
  SPIDER 
  ON 
  HOPS 
  IN 
  CALIFORNIA. 
  

  

  THE 
  ADULT. 
  

  

  Description. 
  — 
  The 
  adults 
  of 
  Tetranychus 
  bimaculatus 
  (figs. 
  3, 
  4) 
  

   are 
  small, 
  greenish 
  yellow 
  or, 
  in 
  some 
  cases, 
  reddish 
  mites 
  ranging 
  

  

  in 
  size 
  from 
  0.27 
  mm. 
  in 
  the 
  male 
  

   to 
  0.50 
  mm. 
  in 
  the 
  female. 
  The 
  

   abdomen 
  j 
  oins 
  the 
  cephalo 
  thorax, 
  

   formed 
  by 
  the 
  fusion 
  of 
  the 
  head 
  

   and 
  thorax, 
  at 
  its 
  full 
  width 
  and 
  

   extends 
  over 
  the 
  portion 
  to 
  

   which 
  the 
  posterior 
  pair 
  of 
  legs 
  

   is 
  attached. 
  The 
  abdomen, 
  the 
  

   cephalothorax, 
  and 
  particularly 
  

   the 
  appendages 
  are 
  well 
  provided 
  

   with 
  hairs. 
  

  

  The 
  two 
  sexes 
  are 
  very 
  distinct. 
  

   The 
  female 
  is 
  much 
  the 
  larger 
  and 
  

   has 
  a 
  broad, 
  rounded 
  abdomen, 
  

   while 
  in 
  the 
  male 
  the 
  abdomen 
  is 
  

   narrow 
  and 
  tapering. 
  These 
  dif- 
  

   ferences 
  are 
  so 
  well 
  marked 
  that 
  

   the 
  sexes 
  may 
  be 
  distinguished 
  

   under 
  an 
  ordinary 
  hand 
  lens. 
  

  

  Fig. 
  3.— 
  The 
  red 
  spider: 
  Adult 
  female, 
  dorsal 
  view. 
  

   Greatly 
  enlarged 
  . 
  ( 
  Original. 
  ) 
  

  

  Copulation. 
  — 
  Copulation 
  begins 
  as 
  

   soon 
  as 
  the 
  mites 
  become 
  adult, 
  the 
  

   female 
  often 
  receiving 
  several 
  males. 
  

   Contrary 
  to 
  the 
  usual 
  method, 
  how- 
  

   ever, 
  the 
  male 
  operates 
  from 
  beneath 
  

   the 
  female. 
  The 
  male 
  mite 
  forces 
  its 
  

   way 
  under 
  the 
  abdomen 
  of 
  the 
  female, 
  

   braces 
  its 
  legs 
  against 
  the 
  leaf, 
  and 
  

   directs 
  the 
  genitalia 
  over 
  its 
  back. 
  

  

  Parthenogenesis. 
  — 
  The 
  idea 
  that 
  par- 
  

   thenogenesis 
  occurs 
  with 
  the 
  red 
  

   spider 
  is 
  an 
  old 
  one, 
  and 
  during 
  this 
  

   investigation 
  a 
  few 
  experiments 
  were 
  

   carried 
  on 
  along 
  this 
  line. 
  A 
  morn- 
  

   ing-glory 
  (Ipomoea 
  sp.) 
  was 
  cleaned 
  

   of 
  all 
  mites 
  and 
  eggs, 
  the 
  petioles 
  

   of 
  the 
  leaves 
  were 
  banded 
  with 
  tree 
  

   tanglefoot, 
  and 
  adult 
  mites 
  were 
  placed 
  upon 
  10 
  of 
  the 
  leaves. 
  After 
  

   eggs 
  were 
  observed 
  the 
  female 
  and 
  all 
  but 
  one 
  of 
  the 
  eggs 
  were 
  

  

  Fig. 
  4.— 
  The 
  red 
  spider: 
  Adult 
  male, 
  dorsal 
  

   view. 
  Greatly 
  enlarged. 
  (Original.) 
  

  

  