﻿660 
  

  

  period. 
  Possibly 
  two 
  species 
  were 
  present, 
  not 
  appearing 
  at 
  the 
  same 
  

   time. 
  Winter 
  washes 
  are 
  not 
  considered 
  to 
  be 
  of 
  any 
  value 
  because 
  

   they 
  are 
  of 
  no 
  use 
  against 
  winter 
  eggs 
  in 
  general, 
  and 
  it 
  will 
  probably 
  

   be 
  found 
  that 
  the 
  eggs 
  of 
  these 
  bugs 
  are 
  deeply 
  embedded 
  in 
  the 
  bark 
  

   of 
  the 
  twigs. 
  References 
  to 
  six 
  papers 
  on 
  the 
  subject 
  of 
  Capsid 
  injury 
  

   are 
  given. 
  

  

  Davidson 
  (J.). 
  The 
  Host 
  Plants 
  and 
  Habits 
  of 
  Aphis 
  rumicis 
  Linn., 
  

   with 
  some 
  observations 
  on 
  the 
  Migration 
  of, 
  and 
  Infestation 
  of 
  

   Plants 
  by 
  Aphides. 
  — 
  Ann. 
  App. 
  Biol., 
  Cambridge 
  Univ. 
  Press, 
  i, 
  

   no. 
  2, 
  July 
  19U, 
  pp. 
  118-141. 
  

  

  According 
  to 
  Theobald, 
  Aphis 
  rumicis 
  has 
  a 
  double 
  life-cycle. 
  In 
  

   one 
  cycle, 
  ova 
  are 
  produced 
  by 
  the 
  sexuparae 
  in 
  late 
  autumn, 
  on 
  

   Rumex 
  ; 
  these 
  hatch 
  in 
  spring, 
  and 
  winged 
  migrants 
  are 
  subsequently 
  

   produced 
  on 
  these 
  plants 
  ; 
  these 
  migrants 
  go 
  about 
  June 
  to 
  broad 
  

   beans, 
  which 
  they 
  infest 
  throughout 
  the 
  summer 
  ; 
  in 
  autumn 
  the 
  

   winged 
  migrants 
  from 
  the 
  broad 
  beans 
  return 
  to 
  Rumex. 
  

  

  In 
  the 
  second 
  Hfe-cycle, 
  ova 
  are 
  produced 
  by 
  the 
  sexuparae 
  on 
  

   Euonymus 
  in 
  late 
  autumn 
  or 
  winter, 
  which 
  hatch 
  in 
  spring 
  ; 
  the 
  winged 
  

   migrants 
  produced 
  migrate 
  to 
  poppies 
  in 
  June, 
  and 
  this 
  form 
  is 
  known 
  

   as 
  Aphis 
  papaveris. 
  In 
  some 
  years, 
  when 
  the 
  number 
  produced 
  is 
  

   abnormal, 
  some 
  of 
  them 
  go 
  from 
  the 
  poppies 
  to 
  mangolds 
  and 
  many 
  

   plants 
  of 
  the 
  family 
  Chenopodiaceae 
  ; 
  in 
  autumn 
  they 
  return 
  to 
  

   Euonymus. 
  

  

  The 
  aphids 
  taken 
  from 
  these 
  different 
  plants 
  showed 
  no 
  structural 
  

   differences, 
  although 
  they 
  differed 
  sHghtly 
  in 
  size 
  or 
  colour 
  on 
  the 
  

   different 
  host 
  plants. 
  If 
  these 
  two 
  parallel 
  Hfe-histories 
  for 
  Aphis 
  

   rumicis 
  are 
  stable, 
  the 
  question 
  of 
  the 
  influence 
  of 
  the 
  host 
  plants 
  

   on 
  aphids 
  becomes 
  an 
  important 
  factor. 
  The 
  tw^o 
  hfe-cycles 
  seemed 
  

   to 
  show 
  that 
  the 
  preceding 
  host 
  plant 
  upon 
  which 
  a 
  generation 
  of 
  aphids 
  

   is 
  produced 
  has 
  a 
  determining 
  influence 
  on 
  the 
  species 
  of 
  plant 
  sub- 
  

   sequently 
  selected 
  by 
  the 
  winged 
  migrants. 
  Theobald 
  found 
  that 
  

   winged 
  viviparous 
  females 
  taken 
  from 
  Euonymus 
  Hved 
  on 
  broad 
  

   beans 
  and 
  gave 
  rise 
  to 
  the 
  " 
  bean 
  black 
  fly," 
  but 
  was 
  unable 
  to 
  trace 
  

   whether 
  the 
  winged 
  migrants 
  from 
  Euonymus 
  went 
  to 
  broad 
  beans, 
  

   and 
  it 
  seemed 
  probable 
  that 
  the 
  two 
  parallel 
  life-cycles 
  might 
  be 
  merged 
  

   into 
  one 
  by 
  crossing 
  from 
  Euonymus 
  to 
  broad 
  beans 
  and 
  from 
  Rumex 
  

   to 
  poppies. 
  If 
  the 
  two 
  hfe-cycles 
  proved 
  to 
  be 
  absolutely 
  constant 
  

   and 
  separate, 
  two 
  biological 
  species 
  would 
  be 
  estabhshed 
  (A. 
  euonymi 
  

   and 
  A. 
  rumicis), 
  resembhng 
  each 
  other 
  in 
  structure, 
  but 
  differing 
  

   physiologically 
  in 
  habits. 
  From 
  the 
  experiments 
  recorded 
  in 
  this 
  

   paper 
  it 
  would 
  appear 
  that 
  A. 
  euonymi 
  will 
  heavily 
  infest 
  broad 
  beans 
  

   and 
  that 
  the 
  same 
  aphis 
  reared 
  on 
  Rumex 
  will 
  heavily 
  infest 
  both 
  broad 
  

   beans 
  and 
  poppies 
  ; 
  thus 
  the 
  two 
  Hfe-cycles 
  may 
  be 
  merged 
  into 
  one. 
  

   The 
  results 
  of 
  a 
  long 
  series 
  of 
  experiments 
  on 
  transference 
  of 
  Aphis 
  

   to 
  various 
  plants 
  are 
  given, 
  and 
  in 
  the 
  author's 
  opinion 
  do 
  not 
  furnish 
  

   suj0&cient 
  evidence 
  that 
  the 
  previous 
  host 
  plant 
  has 
  an 
  influence 
  on 
  

   the 
  degree 
  of 
  infestation 
  of 
  the 
  succeeding 
  ones 
  to 
  which 
  the 
  winged 
  

   migrants 
  were 
  transferred. 
  Winged 
  viviparous 
  females 
  in 
  these 
  

   experiments 
  showed 
  a 
  marked 
  tendency 
  to 
  migrate 
  and 
  collect 
  in 
  vast 
  

   numbers 
  on 
  the 
  top 
  of 
  the 
  musHn 
  bags 
  covering 
  the 
  plants. 
  They 
  

   seemed 
  active 
  and 
  restless 
  and 
  apparently 
  not 
  feeding 
  on 
  the 
  host 
  

  

  