﻿258 
  

  

  E. 
  R. 
  SPEYER. 
  

  

  Lea 
  Valley 
  great 
  numbers 
  of 
  flies 
  have 
  been 
  observed 
  shortly 
  after 
  the 
  introduction 
  

   of 
  the 
  borders 
  into 
  the 
  houses, 
  yet 
  here 
  no 
  damage 
  has 
  resulted 
  to 
  the 
  cucumber 
  plants. 
  

  

  The 
  attack 
  described 
  above 
  followed 
  on 
  a 
  period 
  when 
  the 
  pot-plants 
  had 
  

   admittedly 
  been 
  watered 
  insufficiently, 
  and 
  there 
  is 
  no 
  doubt 
  that 
  the 
  larvae 
  are 
  

   dependent 
  upon 
  a 
  certain 
  moisture 
  content 
  in 
  the 
  soil, 
  a 
  deficiency 
  of 
  which 
  causes 
  

   them 
  to 
  invade 
  the 
  roots 
  of 
  the 
  plant. 
  In 
  making 
  recommendations 
  for 
  control, 
  it 
  

   will 
  be 
  seen 
  that 
  an 
  excess 
  of 
  moisture 
  in 
  the 
  soil 
  is 
  fatal 
  to 
  the 
  life 
  of 
  the 
  larvae, 
  

   but 
  before 
  describing 
  some 
  experiments 
  in 
  this 
  connection 
  mention 
  will 
  be 
  made 
  of 
  

   another 
  Sciarid 
  fly 
  which 
  has 
  appeared 
  as 
  a 
  severe 
  pest, 
  namely, 
  Plastosciara 
  perniciosa, 
  

  

  Fig. 
  8. 
  Plastosciara 
  perniciosa, 
  Edwards, 
  §, 
  pupa, 
  X 
  60. 
  

  

  Edwards 
  (Entomologists' 
  Monthly 
  Magazine, 
  July 
  1922, 
  p. 
  160). 
  This 
  minute 
  black 
  

   fly 
  (fig. 
  7) 
  is 
  very 
  similar 
  to 
  Pnyxia 
  scabiei, 
  but 
  both 
  sexes 
  of 
  the 
  fly 
  have 
  wings. 
  

   Recently 
  there 
  has 
  been 
  a 
  very 
  serious 
  outbreak 
  in 
  cucumber 
  houses 
  in 
  the 
  Worthing 
  

   district, 
  and 
  another 
  attack 
  has 
  been 
  reported 
  from 
  Dartford. 
  The 
  attack 
  has 
  been 
  

   confined 
  to 
  fruiting 
  plants 
  in 
  the 
  border, 
  the 
  hundreds 
  of 
  larvae 
  having 
  reduced 
  the 
  

   tap-root 
  to 
  a 
  pulp, 
  and 
  caused 
  much 
  further 
  damage 
  by 
  removing 
  the 
  cortex 
  of 
  

   the 
  stem 
  just 
  below, 
  and 
  sometimes 
  even 
  above, 
  the 
  soil 
  surface 
  (PI. 
  x, 
  figs. 
  1, 
  2). 
  

   The 
  adult 
  flies 
  swarm 
  in 
  the 
  morning, 
  in 
  bright 
  sunlight, 
  and 
  are 
  found 
  in 
  company 
  

   with 
  Pnyxia 
  scabiei. 
  

  

  Control 
  Measures. 
  

  

  With 
  a 
  view 
  to 
  killing 
  the 
  larvae 
  in 
  the 
  soil, 
  the 
  following 
  chemicals 
  have 
  been 
  

   used 
  : 
  — 
  

  

  Potassium 
  sulphide, 
  2 
  per 
  cent., 
  1 
  per 
  cent., 
  and 
  0-5 
  per 
  cent, 
  solution; 
  

  

  100 
  cc. 
  to 
  the 
  pot, 
  2 
  applications. 
  

   Ammonium 
  carbonate 
  and 
  copper 
  sulphate, 
  2 
  per 
  cent., 
  1 
  per 
  cent., 
  and 
  

  

  0-5 
  per 
  cent, 
  solutions 
  ; 
  100 
  cc. 
  to 
  the 
  pot, 
  2 
  applications. 
  

   Mustard, 
  2 
  per 
  cent., 
  1 
  per 
  cent., 
  and 
  0-5 
  per 
  cent, 
  solutions 
  ; 
  100 
  cc. 
  to 
  

  

  the 
  pot, 
  2 
  applications. 
  

   Calcium 
  chloride 
  . 
  . 
  . 
  . 
  . 
  . 
  5 
  per 
  cent, 
  solution 
  on 
  larvae. 
  

  

  Ammonium 
  carbonate 
  

   Nitric 
  acid 
  

  

  Hydrochloric 
  acid 
  . 
  . 
  

   Potassium 
  bichromate 
  

   Potassium 
  permanganate 
  

   Ammonia 
  

  

  1 
  per 
  cent, 
  solu 
  

  

  and 
  on 
  soil. 
  

  

  ion 
  on 
  larvae. 
  

  

  Except 
  for 
  hydrochloric 
  acid, 
  which 
  is 
  dangerous 
  to 
  use 
  on 
  plants, 
  none 
  of 
  these 
  

   substances 
  gave 
  any 
  appreciable 
  result. 
  During 
  the 
  experiments, 
  however, 
  some 
  

   larvae 
  were 
  immersed 
  in 
  water, 
  and 
  it 
  was 
  found 
  that 
  they 
  died 
  in 
  about 
  an 
  hour's 
  time. 
  

  

  