﻿232 
  

  

  barley 
  four 
  generations 
  were 
  observed 
  from 
  November 
  1912 
  to 
  June 
  

   1913. 
  Heat 
  and 
  moisture 
  favour 
  the 
  pest, 
  as 
  they 
  do 
  the 
  plant. 
  

   Dryness 
  retards 
  development, 
  and 
  the 
  author 
  has 
  kept 
  pupae 
  for 
  a 
  

   year 
  in 
  dry 
  surroundings 
  and 
  then 
  caused 
  them 
  to 
  transform 
  into 
  

   adults 
  by 
  placing 
  them 
  in 
  damp 
  air. 
  This 
  proves 
  that 
  pupae 
  left 
  in 
  

   the 
  stubble 
  after 
  harvesting 
  are 
  able 
  to 
  resist 
  the 
  unfavourable 
  con- 
  

   ditions. 
  In 
  Tunisia 
  numerous 
  entomophagous 
  parasites 
  attack 
  

   Mayetiola 
  destructor 
  and 
  six 
  species 
  of 
  Chalcids 
  and 
  two 
  species 
  of 
  

   Braconids 
  were 
  obtained 
  by 
  breeding. 
  At 
  the 
  time 
  the 
  adults 
  of 
  the 
  

   first 
  generation 
  appeared 
  in 
  February 
  1912 
  hardly 
  10 
  per 
  cent, 
  of 
  the 
  

   pupae 
  were 
  parasitised 
  ; 
  of 
  the 
  second 
  generation 
  in 
  March 
  about 
  30 
  

   per 
  cent, 
  were 
  parasitised, 
  and 
  by 
  the 
  end 
  of 
  April 
  the 
  figure 
  was 
  80 
  

   per 
  cent. 
  The 
  author 
  discontinued 
  observation 
  as 
  he 
  believed 
  complete 
  

   control 
  had 
  been 
  attained. 
  He 
  was 
  therefore 
  surprised 
  to 
  find 
  a 
  

   certain 
  number 
  of 
  flies 
  in 
  the 
  fields 
  in 
  February 
  1913. 
  On 
  investi- 
  

   gating 
  this, 
  a 
  number 
  of 
  dry-stored 
  pupae 
  from 
  the 
  Saint-Cyprien 
  

   estate 
  were 
  examined, 
  and 
  it 
  was 
  found 
  that 
  while 
  80 
  per 
  cent, 
  had 
  

   been 
  parasitised, 
  the 
  remainder 
  were 
  still 
  living 
  and 
  transformed 
  into 
  

   adults 
  Avhen 
  kept 
  in 
  damp 
  air 
  for 
  three 
  weeks. 
  In 
  April 
  and 
  May 
  

   infested 
  barley 
  was 
  collected 
  and 
  kept 
  dry 
  ; 
  the 
  parasites 
  hatched 
  

   out, 
  but 
  the 
  Cecidomyias 
  remained 
  in 
  a 
  state 
  of 
  arrest. 
  The 
  damage 
  

   done 
  by 
  this 
  pest 
  amounts 
  to 
  many 
  millions 
  of 
  francs 
  in 
  Algeria 
  and 
  

   Tunisia. 
  Experiments 
  appear 
  to 
  prove 
  that 
  the 
  more 
  water 
  a 
  cereal 
  

   contains 
  the 
  more 
  open 
  it 
  is 
  to 
  attack. 
  In 
  hot, 
  dry 
  climates 
  those 
  

   species 
  which 
  contain 
  the 
  least 
  water 
  will 
  show 
  the 
  most 
  resistance. 
  

   As 
  yet 
  the 
  ravages 
  in 
  wheat 
  in 
  Tunisia 
  have 
  not 
  reached 
  such 
  a 
  pitch 
  

   as 
  to 
  permit 
  of 
  picking 
  out 
  the 
  varieties 
  most 
  capable 
  of 
  resistance. 
  

   Barley 
  is 
  badly 
  attacked, 
  and 
  as 
  the 
  most 
  vigorous 
  plants 
  contain 
  the 
  

   most 
  water, 
  they 
  are 
  also 
  the 
  most 
  susceptible. 
  In 
  spite 
  of 
  this 
  they 
  

   have 
  a 
  surplus 
  margin 
  of 
  vigour 
  which 
  compensates 
  to 
  a 
  large 
  degree 
  

   for 
  the 
  losses 
  caused 
  by 
  the 
  pest. 
  Late 
  sowing 
  is 
  a 
  good 
  preventive 
  

   when 
  the 
  winter 
  is 
  sufiiciently 
  cold 
  to 
  hold 
  back 
  the 
  pest. 
  Where 
  the 
  

   latter 
  is 
  rare 
  in 
  October, 
  wheat, 
  barley 
  and 
  rye 
  germinate 
  safely 
  if 
  

   sown 
  late. 
  In 
  hot 
  cUmates 
  this 
  method 
  has 
  no 
  value. 
  In 
  Tunisia 
  

   stubble-burning 
  between 
  the 
  15th 
  July 
  and 
  the 
  15th 
  September 
  is 
  

   very 
  efficacious, 
  because 
  the 
  fly 
  is 
  then 
  passing 
  through 
  its 
  larval 
  or 
  

   nymphal 
  stages 
  in 
  the 
  arrested 
  state, 
  and 
  its 
  parasites 
  have 
  already 
  

   emerged. 
  Owing 
  to 
  the 
  danger 
  of 
  field 
  and 
  forest 
  fires 
  burning 
  is 
  

   subject 
  to 
  certain 
  regulations 
  in 
  Tunisia. 
  These 
  regulations 
  also 
  

   require 
  the 
  destruction 
  of 
  the 
  debris 
  from 
  threshing, 
  as 
  this 
  is 
  liable 
  

   to 
  contain 
  pupae 
  of 
  M. 
  destructor. 
  Alternation 
  of 
  crops 
  would 
  be 
  a 
  

   very 
  practical 
  and 
  economical 
  method 
  did 
  not 
  the 
  wind 
  aid 
  in 
  diffusing 
  

   the 
  pest, 
  for 
  the 
  Cecidomyia 
  only 
  spreads 
  slowly. 
  Of 
  curative 
  methods, 
  

   the 
  author 
  states 
  that 
  rolling 
  is 
  ineffective, 
  because 
  of 
  the 
  elasticity 
  

   and 
  unevenness 
  of 
  the 
  soil. 
  Insecticides 
  are 
  equally 
  ineffective, 
  

   because 
  the 
  generations 
  follow 
  without 
  any 
  order. 
  Pasturing 
  sheep 
  

   on 
  infested 
  fields 
  and 
  mowing 
  the 
  green 
  crop 
  may 
  be 
  considered 
  in 
  

   rich 
  soils, 
  for 
  the 
  larva 
  would 
  thus 
  be 
  killed 
  before 
  it 
  can 
  reach 
  the 
  

   neighbourhood 
  of 
  the 
  collar. 
  The 
  more 
  water 
  a 
  cereal 
  contains 
  

   the 
  more 
  susceptible 
  it 
  is 
  to 
  attack 
  ; 
  entomophagous 
  parasites 
  

   may 
  play 
  an 
  important 
  role 
  in 
  control 
  ; 
  stubble-burning 
  

   destroys 
  the 
  pest 
  and 
  favours 
  its 
  parasite. 
  It 
  should 
  be 
  made 
  

   compulsory 
  in 
  infested 
  districts. 
  The 
  wheat 
  weevil 
  Calandra 
  

  

  