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  (2) 
  that 
  it 
  is 
  most 
  unlikely 
  that 
  any 
  migrations 
  take 
  place 
  ; 
  (3) 
  that 
  

   the 
  decrease 
  in 
  their 
  numbers 
  depends 
  upon 
  the 
  decrease 
  in 
  the 
  

   fertility 
  of 
  the 
  viviparous 
  females 
  ; 
  dissections 
  of 
  females 
  taken 
  at 
  

   different 
  periods 
  of 
  the 
  season 
  have 
  shown 
  that 
  their 
  fertility 
  remains 
  

   constant 
  from 
  May 
  to 
  July, 
  while 
  it 
  decreases 
  by 
  one-half 
  in 
  August. 
  

  

  Aphis 
  sorbi 
  was 
  TSiie. 
  The 
  author 
  did 
  not 
  find 
  them 
  on 
  cultivated 
  

   fruit 
  trees, 
  although 
  other 
  observers 
  report 
  that 
  they 
  attack 
  apple. 
  

  

  Aphis 
  crataegi. 
  According 
  to 
  Mordvilko 
  this 
  species 
  migrates 
  

   during 
  the 
  summer 
  from 
  the 
  white 
  thorn 
  to 
  certain 
  grasses 
  which 
  serve 
  

   as 
  intermediate 
  hosts 
  ; 
  the 
  second 
  generation 
  consists 
  almost 
  exclusively 
  

   of 
  winged 
  migrating 
  females, 
  which 
  start 
  a 
  new 
  generation 
  on 
  

   Ranunculus. 
  These 
  were 
  previously 
  considered 
  to 
  be 
  a 
  distinct 
  species, 
  

   Aphis 
  ranunculi, 
  Kit. 
  The 
  author's 
  observations 
  have 
  confirmed 
  

   the 
  statements 
  of 
  Mordvilko. 
  Besides 
  white 
  thorn, 
  he 
  found 
  the 
  

   stem-mothers 
  also 
  on 
  apple 
  trees. 
  On 
  the 
  same 
  trees 
  he 
  found 
  also, 
  

   inside 
  some 
  curled 
  leaves, 
  aphids 
  which 
  strongly 
  resembled 
  specimens 
  

   of 
  A. 
  crataegi, 
  and 
  which 
  were 
  described 
  by 
  Kaltenbach 
  as 
  a 
  genera- 
  

   tion 
  living 
  specially 
  on 
  apple 
  trees. 
  According 
  to 
  Mordvilko 
  A. 
  

   crataegi 
  migrates 
  also 
  to 
  Aethusa 
  (fool's 
  parsley). 
  The 
  damage 
  done 
  

   by 
  the 
  form 
  found 
  on 
  apple 
  trees 
  is 
  very 
  great. 
  The 
  author 
  reared 
  

   from 
  the 
  stem-mothers 
  of 
  A. 
  crataegi, 
  a 
  parasite, 
  identified 
  by 
  Kurd- 
  

   jumov 
  (by 
  whom 
  all 
  the 
  other 
  parasites 
  mentioned 
  were 
  also 
  identified) 
  

   as 
  Ephedrus 
  lacertosus, 
  Hal. 
  

  

  Phorodon 
  humidi 
  lives 
  on 
  thorn 
  bushes, 
  on 
  Prunus 
  insiticia, 
  L. 
  

   (bullace), 
  and 
  on 
  plum 
  trees, 
  migrating 
  to 
  Humulus 
  lupulus, 
  L. 
  (hops). 
  

   At 
  the 
  same 
  time 
  the 
  author 
  found 
  that 
  some 
  individuals 
  pass 
  the 
  

   whole 
  summer 
  on 
  plum 
  trees. 
  Those 
  found 
  during 
  the 
  summer 
  on 
  

   hops 
  are 
  exclusively 
  wingless 
  females, 
  only 
  the 
  last 
  generation, 
  con- 
  

   sisting 
  of 
  winged 
  specimens, 
  migrating 
  back 
  to 
  the 
  plum 
  trees. 
  These 
  

   aphids 
  do 
  not 
  visibly 
  injure 
  plum 
  trees, 
  but 
  cause 
  great 
  damage 
  to 
  

   hops, 
  being 
  the 
  most 
  dangerous 
  pest 
  of 
  these 
  plants. 
  

  

  Myzus 
  cerasi 
  was 
  found 
  by 
  the 
  author 
  during 
  the 
  whole 
  summer, 
  

   after 
  9th 
  June, 
  on 
  cherries, 
  there 
  being 
  practically 
  no 
  winged 
  females. 
  

   His 
  observations 
  did 
  not 
  confirm 
  the 
  statement 
  by 
  Kessler 
  that 
  these 
  

   aphides 
  migrate 
  in 
  the 
  summer, 
  although 
  he 
  is 
  unable 
  definitely 
  to 
  

   dispute 
  this 
  statement. 
  The 
  damage 
  done 
  by 
  them 
  to 
  cherry 
  trees 
  is 
  

   very 
  great, 
  when 
  they 
  appear 
  in 
  large 
  numbers. 
  The 
  author 
  found 
  

   the 
  following 
  insect 
  enemies 
  : 
  Larvae 
  of 
  a 
  Chrysopid, 
  of 
  Bremia 
  and 
  of 
  

   Syrphid 
  flies 
  ; 
  imagos 
  of 
  Coccinelta 
  bipunctata, 
  L. 
  ; 
  he 
  found 
  also 
  

   empty 
  skins 
  of 
  aphids, 
  from 
  which 
  some 
  parasite 
  had 
  emerged. 
  

  

  Hyalopterus 
  pruni. 
  The 
  author 
  confirms 
  the 
  discovery 
  by 
  Mordvilko 
  

   that 
  this 
  is 
  synonymous 
  with 
  H. 
  arundinis, 
  F., 
  which 
  is 
  found 
  in 
  

   summer 
  on 
  reeds, 
  to 
  which 
  they 
  migrate 
  from 
  plum 
  trees, 
  returning 
  to 
  

   the 
  latter 
  in 
  autumn. 
  Some, 
  however, 
  do 
  not 
  migrate 
  at 
  all, 
  so 
  that 
  

   from 
  June 
  to 
  August 
  they 
  can 
  be 
  found 
  on 
  both 
  the 
  primary 
  and 
  

   intermediate 
  host 
  plants. 
  Besides 
  plum 
  trees 
  they 
  are 
  also 
  found 
  on 
  

   apricots, 
  peach 
  trees, 
  thorn-bushes 
  {Prunus 
  spinosa, 
  L.) 
  and 
  on 
  

   Prunus 
  insiticia, 
  L. 
  The 
  sucking 
  of 
  these 
  aphids 
  affects 
  the 
  leaves 
  

   but 
  little, 
  but 
  they 
  assist 
  the 
  development 
  of 
  a 
  fungus 
  {Capnodium 
  

   salicinum, 
  Mont.), 
  and 
  cause 
  considerable 
  damage 
  by 
  attacking 
  unripe 
  

   fruits 
  at 
  the 
  beginning 
  of 
  summer. 
  These 
  aphids 
  Avere 
  found 
  to 
  be 
  

   destroyed 
  by 
  Syrphid 
  larvae 
  and 
  by 
  those 
  of 
  Bremia 
  ; 
  many 
  specimens 
  

  

  