﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  365 
  

  

  Making 
  allowances 
  for 
  error 
  at 
  every 
  point, 
  it 
  is 
  clear 
  that 
  density 
  of 
  infestation 
  

   being 
  equal, 
  the 
  fly 
  is 
  several 
  hundred 
  times 
  more 
  likely 
  to 
  feed 
  upon 
  man 
  where 
  

   wild 
  hosts 
  are 
  very 
  few 
  and 
  female 
  percentage 
  very 
  high 
  than 
  when 
  they 
  are 
  very 
  

   many 
  and 
  female 
  percentage 
  low. 
  

  

  II 
  (e). 
  Female 
  Percentage 
  as 
  an 
  Index 
  to 
  the 
  Chances 
  favouring 
  Transmission 
  of 
  

   Human 
  Trypanosomiasis. 
  

  

  Perhaps 
  the 
  most 
  pertinent 
  point 
  in 
  this 
  connection 
  is 
  that 
  the 
  chances 
  favouring 
  

   transmission 
  of 
  the 
  virus 
  of 
  sleeping 
  sickness 
  from 
  man 
  to 
  man 
  are 
  vastly 
  less 
  

   proportionately 
  when 
  few 
  flies 
  feed 
  on 
  man 
  than 
  when 
  many 
  do 
  so. 
  The 
  same 
  fly 
  

   must 
  feed 
  on 
  or 
  bite 
  the 
  human 
  host 
  twice 
  in 
  order 
  to 
  transmit 
  disease 
  from 
  an 
  

   infected 
  to 
  a 
  healthy 
  man. 
  If 
  only 
  one 
  fly 
  in 
  500 
  or 
  1,000 
  actually 
  bites 
  man, 
  the 
  

   chances 
  that 
  that 
  same 
  fly 
  will 
  attack 
  man 
  a 
  second 
  time 
  are 
  absurdly 
  small 
  ; 
  if 
  

   every 
  second 
  or 
  third 
  fly 
  feeds 
  upon 
  or 
  bites 
  man 
  the 
  chances 
  that 
  the 
  same 
  fly 
  will 
  

   attack 
  man 
  a 
  second 
  time 
  are 
  stupendous 
  in 
  comparison. 
  

  

  The 
  female 
  percentage 
  may 
  thus 
  be 
  a 
  very 
  valuable 
  index 
  to 
  the 
  chances 
  favouring 
  

   transmission 
  of 
  human 
  disease. 
  

  

  III. 
  The 
  Long-shore 
  Movements 
  of 
  Glossina 
  palpalis. 
  

  

  The 
  explanation 
  of 
  the 
  variable 
  ratio 
  between 
  the 
  sexes 
  of 
  Glossina 
  palpalis 
  provided 
  

   by 
  the 
  early 
  experiments 
  proved 
  inapplicable 
  in 
  many 
  cases, 
  and 
  numerous 
  vagaries 
  

   in 
  the 
  sex 
  ratio 
  were 
  observed 
  which 
  were 
  for 
  long 
  inexplicable. 
  

  

  Eventually 
  investigations 
  into 
  the 
  long-shore 
  movements 
  of 
  flies 
  and 
  the 
  routes 
  

   and 
  courses 
  followed 
  by 
  them 
  in 
  their 
  food-hunting 
  and 
  otherwise 
  stimulated 
  flights, 
  

   led 
  back 
  into 
  the 
  old 
  problem 
  of 
  sex 
  disparity 
  and 
  provided 
  logical 
  explanation 
  

   for 
  many 
  variations 
  in 
  it 
  which 
  had 
  been 
  observed 
  but 
  which 
  could 
  not 
  be 
  correlated 
  

   with 
  abundance 
  or 
  scarcity 
  of 
  food. 
  The 
  same 
  study 
  also 
  required 
  consideration 
  

   of 
  " 
  shelter" 
  (arborescent 
  vegetation 
  sought 
  or 
  required 
  by 
  the 
  flies 
  for 
  their 
  protection) 
  

   and 
  of 
  the 
  relative 
  attractiveness 
  of 
  different 
  types 
  of 
  it. 
  

  

  These 
  three, 
  quite 
  different 
  topics 
  — 
  sex 
  disparity, 
  shelter, 
  and 
  movements 
  of 
  flies 
  

   from 
  place 
  to 
  place 
  — 
  had 
  to 
  be 
  considered 
  coincidently 
  in 
  the 
  field 
  and 
  cannot 
  

   be 
  entirely 
  separated 
  in 
  reporting 
  upon 
  field 
  work. 
  

  

  In 
  the 
  following 
  sub-sections 
  they 
  are 
  discussed 
  as 
  they 
  were 
  studied, 
  inter- 
  

   dependently. 
  

  

  III 
  (a). 
  Experiment 
  to 
  test 
  the 
  Movements 
  of 
  Flies 
  along 
  the 
  Lake 
  Shore. 
  

  

  The 
  larger 
  catches 
  of 
  fly 
  made 
  on 
  Bulago 
  Island 
  and 
  recorded 
  in 
  Table 
  I 
  were 
  

   from 
  near 
  the 
  extremity 
  of 
  a 
  long, 
  narrow 
  spit 
  of 
  sandy 
  land 
  designated 
  in 
  the 
  

   notes 
  as 
  "Crocodile 
  Point" 
  (see 
  Fig. 
  I). 
  The 
  area 
  of 
  this 
  spit 
  was 
  considerably 
  

   less 
  than 
  of 
  the 
  islet 
  of 
  Lula, 
  from 
  which 
  the 
  flies 
  were 
  caught 
  as 
  recorded 
  in 
  Tables 
  

   VI 
  and 
  VII. 
  But 
  though 
  these 
  catching 
  experiments 
  on 
  Lula 
  quickly 
  brought 
  

   about 
  reduction 
  in 
  density 
  of 
  active 
  flies, 
  it 
  was 
  observed 
  that 
  no 
  such 
  effect 
  was 
  

   produced 
  on 
  the 
  density 
  of 
  the 
  fly 
  at 
  Crocodile 
  Point. 
  On 
  the 
  contrary, 
  although 
  

   more 
  than 
  2,000 
  flies 
  were 
  caught 
  there 
  during 
  the 
  period 
  10th 
  to 
  13th 
  November, 
  

   neither 
  density 
  nor 
  female 
  percentage 
  underwent 
  notable 
  change 
  (see 
  Table 
  XII). 
  

   (659) 
  b2 
  

  

  