﻿153 
  

  

  this 
  point 
  definitively 
  winter-eggs 
  must 
  be 
  obtained 
  and 
  the 
  larvae 
  

   which 
  hatch 
  out 
  in 
  spring 
  must 
  be 
  placed 
  on 
  European 
  and 
  American 
  

   elms, 
  and 
  also 
  on 
  apple-trees. 
  Details 
  are 
  given 
  of 
  some 
  experiments 
  

   carried 
  out 
  by 
  the 
  Experiment 
  Station 
  at 
  Wadenswil 
  with 
  the 
  object 
  

   of 
  breeding 
  winter-eggs 
  for 
  infection 
  tests. 
  The 
  result 
  of 
  these 
  

   experiments 
  was 
  that 
  about 
  500 
  winged 
  individuals 
  produced 
  200 
  

   females 
  and 
  70 
  males, 
  which 
  in 
  turn 
  have 
  given 
  as 
  yet 
  42 
  living 
  

   winter-eggs. 
  Though 
  not 
  especially 
  favourable, 
  this 
  is 
  satisfactory 
  

   when 
  compared 
  with 
  former 
  attempts. 
  

  

  Moore 
  (B. 
  A.). 
  The 
  Wheat 
  Louse 
  [Toxoptera 
  graminum). 
  — 
  Agric. 
  

   Jl. 
  Union 
  S. 
  Africa, 
  Pretoria, 
  vi, 
  no. 
  3, 
  Sept. 
  1913, 
  pp. 
  482-492, 
  

   12 
  figs; 
  vi, 
  no. 
  5, 
  Nov. 
  1913, 
  pp. 
  767-772 
  ; 
  vi, 
  no. 
  6, 
  Dec. 
  1913, 
  

   pp. 
  973-977 
  ; 
  vii, 
  no. 
  1, 
  Jan. 
  1914, 
  pp. 
  50-60. 
  

  

  In 
  South 
  Africa 
  the 
  first 
  record 
  of 
  the 
  wheat 
  louse 
  is 
  in 
  the 
  1903-04 
  

   report 
  of 
  the 
  Manager 
  of 
  the 
  Potchefstroom 
  Experimental 
  Farm, 
  but 
  

   according 
  to 
  old 
  farmers 
  the 
  pest 
  had 
  been 
  present 
  for 
  many 
  years 
  

   before. 
  It 
  is 
  generally 
  distributed 
  over 
  the 
  wheat-growing 
  districts 
  

   having 
  an 
  altitude 
  of 
  between 
  3,500 
  and 
  5,000 
  feet. 
  In 
  South 
  Africa 
  

   there 
  seem 
  to 
  be 
  but 
  two 
  forms 
  of 
  the 
  insect, 
  namely, 
  the 
  winged 
  

   migratory 
  females 
  and 
  the 
  apterous 
  females 
  ; 
  males 
  and 
  oviparous 
  

   females 
  have 
  not 
  been 
  seen. 
  

  

  All 
  the 
  individuals 
  of 
  the 
  wheat 
  louse 
  reach 
  maturity 
  in 
  about 
  seven 
  

   days 
  from 
  birth 
  and 
  produce 
  young 
  without 
  fertilisation. 
  During 
  

   summer 
  the 
  louse 
  lives 
  about 
  32 
  days, 
  producing, 
  under 
  favourable 
  

   conditions, 
  three 
  young 
  daily 
  for 
  a 
  period 
  of 
  25 
  days. 
  These 
  are 
  the 
  

   conditions 
  in 
  the 
  wheat 
  fields 
  about 
  August, 
  September 
  and 
  October. 
  

   About 
  the 
  end 
  of 
  October 
  or 
  the 
  beginning 
  of 
  November 
  the 
  grain, 
  

   approaching 
  maturity, 
  becomes 
  too 
  tough 
  for 
  the 
  wheat 
  louse. 
  By 
  

   this 
  time 
  the 
  winged 
  females 
  have 
  developed, 
  leaving 
  the 
  grain 
  and 
  

   seeking 
  out 
  grasses 
  upon 
  which 
  they 
  can 
  spend 
  the 
  summer 
  when 
  no 
  

   cereals 
  are 
  available. 
  If, 
  as 
  a 
  result 
  of 
  drought, 
  there 
  is 
  no 
  grass, 
  the 
  

   great 
  majority 
  of 
  the 
  aphids 
  die 
  ; 
  but 
  some 
  of 
  them 
  are 
  saved 
  by 
  a 
  

   common 
  ant, 
  Plagiolepis 
  custodiens, 
  Sm., 
  which 
  carries 
  them 
  off 
  and 
  

   places 
  them 
  on 
  the 
  underground 
  stems 
  or 
  roots 
  of 
  the 
  grasses 
  on 
  which 
  

   they 
  can 
  live. 
  Here 
  they 
  are 
  tended 
  by 
  the 
  ants, 
  which 
  are 
  repaid 
  by 
  

   honey 
  dew 
  secreted 
  by 
  the 
  aphids. 
  

  

  The 
  wheat 
  louse 
  may 
  be 
  found 
  upon 
  wheat, 
  oats, 
  rye, 
  or 
  barley 
  ; 
  

   during 
  winter 
  it 
  occurs 
  on 
  the 
  main 
  cereal 
  crop, 
  during 
  summer 
  on 
  

   stray 
  plants. 
  If 
  there 
  are 
  no 
  cereal 
  crops 
  in 
  winter, 
  the 
  louse 
  is 
  found 
  

   on 
  fescue 
  grass 
  (Bromus 
  willdenowii). 
  During 
  summer 
  it 
  frequents 
  

   different 
  grasses, 
  such 
  as 
  Johnstone 
  grass 
  (Sorghum 
  halepense), 
  goose- 
  

   grass 
  {Eleusine 
  indica), 
  sweet 
  grass 
  (Panicum 
  laevifolium), 
  teff 
  grass 
  

   and 
  millet 
  ; 
  C. 
  P. 
  van 
  der 
  Merwe 
  mentions 
  also 
  kweek 
  grass 
  (Cynodon 
  

   dactylon) 
  as 
  a 
  host 
  plant. 
  The 
  louse 
  has 
  not 
  been 
  found 
  on 
  Paspalum 
  

   dilatatum, 
  even 
  when 
  growing 
  side 
  by 
  side 
  with 
  infested 
  Johnstone 
  

   grass. 
  

  

  In 
  the 
  United 
  States 
  a 
  very 
  small 
  Braconid 
  wasp 
  (Aphidiiis 
  testiceipes) 
  

   successfully 
  controls 
  the 
  wheat 
  louse. 
  In 
  South 
  Africa 
  several 
  species 
  

   of 
  Aphidiiis 
  occur, 
  one 
  of 
  which 
  multiplies 
  rapidly 
  under 
  favourable 
  

   conditions. 
  Should 
  the 
  wheat 
  louse 
  not 
  be 
  abundant 
  in 
  the 
  field, 
  the 
  

   Aphidius 
  is 
  able 
  to 
  breed 
  in 
  certain 
  other 
  species 
  of 
  aphids, 
  but 
  directly 
  

  

  