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  the 
  Toxoptera 
  become 
  more 
  abundant 
  the 
  Aphidius 
  returns 
  to 
  them. 
  

   An 
  important 
  predaceous 
  insect 
  is 
  the 
  black-spotted 
  ladybird 
  {Adalia 
  

   flaiwnaculata), 
  which 
  during 
  the 
  larval 
  and 
  adult 
  stages 
  feeds 
  on 
  

   T. 
  graminum 
  and 
  a 
  large 
  number 
  of- 
  other 
  aphids 
  ; 
  the 
  red-spotted 
  lady- 
  

   bird 
  (Chilomenes 
  hinata) 
  and 
  the 
  black 
  ladybird 
  (Exocliomus 
  nigro- 
  

   maculatus) 
  are 
  also 
  important 
  predators. 
  Of 
  the 
  several 
  different 
  species 
  

   of 
  Syrphid 
  flies, 
  the 
  larvae 
  of 
  which 
  feed 
  upon 
  T. 
  graminum, 
  XantJio- 
  

   gramma 
  scutellare 
  is 
  the 
  most 
  important. 
  The 
  lace- 
  wing 
  flies 
  (Chrysopa 
  

   sp.) 
  are 
  of 
  less 
  value. 
  The 
  ladybirds 
  and 
  Syrphids 
  are 
  themselves 
  

   attacked 
  by 
  parasites 
  ; 
  the 
  former 
  by 
  a 
  Braconid 
  wasp 
  [Dinocampus 
  

   sp.) 
  and 
  a 
  Chalcid 
  {Homalotylus 
  sp.), 
  the 
  latter 
  by 
  an 
  Ichneumon, 
  

   Bassus 
  laetatorius. 
  The 
  Syrphid 
  is 
  of 
  considerable 
  value 
  as 
  it 
  is 
  the 
  

   first 
  enemy 
  to 
  appear 
  in 
  an 
  infested 
  field. 
  Owing 
  to 
  the 
  abundance 
  

   of 
  ladybirds, 
  the 
  value 
  of 
  the 
  Aphidius 
  is 
  not 
  so 
  great 
  in 
  South 
  Africa 
  

   as 
  in 
  America. 
  A 
  ladybird 
  will 
  destroy 
  a 
  given 
  number 
  of 
  wheat 
  lice 
  

   in 
  a 
  shorter 
  time 
  than 
  will 
  the 
  Aphidius, 
  but 
  while 
  it 
  is 
  feeding 
  on 
  the 
  

   lice 
  it 
  is 
  also 
  destroying 
  the 
  Aphidius. 
  After 
  the 
  work 
  of 
  all 
  the 
  

   parasites 
  and 
  other 
  enemies, 
  a 
  few 
  individuals 
  or 
  colonies 
  of 
  the 
  aphis 
  

   remain 
  to 
  carry 
  on 
  the 
  species. 
  On 
  Johnstone 
  grass 
  the 
  individuals 
  

   underground 
  always 
  furnish 
  a 
  source 
  from 
  which 
  new 
  colonies 
  can 
  be 
  

   formed, 
  and 
  the 
  insects 
  are 
  able 
  to 
  pass 
  through 
  the 
  summer 
  success- 
  

   fully, 
  although 
  greatly 
  reduced 
  in 
  numbers. 
  Under 
  cold 
  conditions, 
  

   however, 
  the 
  balance 
  is 
  in 
  favour 
  of 
  the 
  wheat 
  louse. 
  The 
  Aphidius 
  

   may 
  be 
  neglected 
  as 
  a 
  means 
  of 
  control 
  below 
  a 
  mean 
  of 
  55° 
  F., 
  w^hile 
  

   the 
  louse 
  is 
  still 
  breeding 
  well 
  as 
  low 
  as 
  50° 
  F., 
  and 
  is 
  not 
  greatly 
  

   retarded 
  until 
  a 
  mean 
  temperature 
  below 
  40° 
  F. 
  is 
  reached. 
  Of 
  the 
  lady- 
  

   birds, 
  the 
  effect 
  of 
  cold 
  seems 
  to 
  be 
  greatest 
  on 
  the 
  Exochomus 
  ; 
  the 
  

   Adalia 
  withstands 
  the 
  cold 
  much 
  better 
  than 
  either 
  of 
  the 
  other 
  two 
  

   and 
  is 
  quite 
  active 
  at 
  50° 
  F. 
  Adult 
  Syrphid 
  flies 
  can 
  almost 
  always 
  

   be 
  found 
  all 
  through 
  the 
  winter, 
  though 
  they 
  breed 
  very 
  slow^ly, 
  and 
  

   their 
  parasite 
  (Bassus) 
  persists 
  with 
  them. 
  

  

  As 
  a 
  general 
  rule 
  aphids 
  can 
  be 
  controlled 
  by 
  spraying 
  the 
  plants 
  

   with 
  paraffin 
  emulsion 
  or 
  tobacco 
  extract 
  and 
  soap, 
  but 
  since 
  a 
  field 
  

   sprayer 
  would 
  have 
  to 
  be 
  used, 
  this 
  entails 
  a 
  large 
  expenditure 
  which 
  

   would 
  practically 
  take 
  all 
  the 
  profit 
  on 
  the 
  wheat. 
  On 
  this 
  account 
  

   the 
  main 
  measures 
  should 
  be 
  directed 
  to 
  prevent 
  the 
  attack. 
  The 
  

   best 
  prevention 
  of 
  a 
  serious 
  loss 
  is 
  irrigation, 
  and 
  where 
  irrigation 
  is 
  

   not 
  feasible 
  the 
  ground 
  should 
  be 
  carefully 
  prepared 
  so 
  as 
  to 
  conserve 
  as 
  

   much 
  moisture 
  as 
  possible. 
  The 
  ground 
  should 
  always 
  be 
  rolled. 
  

   Under 
  irrigation, 
  fertilisers 
  can 
  be 
  used 
  to 
  make 
  a 
  strong 
  healthy 
  plant 
  

   able 
  to 
  withstand 
  the 
  attack. 
  Good 
  rotten 
  farmyard 
  manure 
  is 
  the 
  best 
  

   fertiliser 
  for 
  this 
  purpose, 
  and 
  the 
  best 
  results 
  would 
  be 
  obtained 
  if 
  

   it 
  were 
  applied 
  in 
  the 
  early 
  spring. 
  Barley 
  is 
  most 
  severely 
  attacked 
  

   by 
  the 
  wheat 
  louse 
  in 
  South 
  Africa 
  ; 
  rye 
  could 
  be 
  better 
  grown 
  than 
  

   barley, 
  and 
  the 
  variety 
  of 
  oats 
  known 
  as 
  winter 
  oats 
  is 
  only 
  slightly 
  

   attacked 
  by 
  the 
  louse. 
  Of 
  the 
  varieties 
  of 
  wheat 
  tested 
  for 
  resistance 
  

   to 
  the 
  louse, 
  "Spring 
  Wheat," 
  ''Wit 
  Klein 
  Koren," 
  ''Russian 
  

   Kubanka 
  Durum," 
  " 
  Bombay 
  " 
  and 
  " 
  Minnesota 
  " 
  seemed 
  the 
  best. 
  

   If 
  an 
  attack 
  starts 
  in 
  one 
  part 
  of 
  a 
  field 
  and 
  the 
  rest 
  of 
  the 
  field 
  is 
  com- 
  

   paratively 
  free, 
  that 
  area 
  should 
  be 
  burned 
  down. 
  If 
  such 
  spots 
  are 
  

   promptly 
  dealt 
  with 
  the 
  whole 
  field 
  may 
  be 
  saved. 
  The 
  use 
  of 
  the 
  

   brush 
  drag 
  or 
  the 
  roller 
  is 
  said 
  to 
  give 
  good 
  results, 
  but 
  it 
  is 
  doubtful 
  

   if 
  they 
  are 
  really 
  worth 
  the 
  labour. 
  Probably 
  the 
  best 
  treatment 
  of 
  an 
  

  

  