﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  OLOSSINA 
  PALPALIS. 
  

  

  389 
  

  

  T 
  (g). 
  The 
  Sex 
  Ratio 
  at 
  Points 
  where 
  Range 
  is 
  extended 
  inland. 
  

  

  In 
  the 
  records 
  of 
  catches 
  at 
  inland 
  points 
  which 
  have 
  been 
  given 
  in 
  the 
  preceding 
  

   paragraphs 
  a 
  very 
  significant 
  feature 
  is 
  the 
  falling 
  off 
  of 
  female 
  percentage 
  coinci- 
  

   dently 
  with 
  the 
  falling 
  off 
  of 
  male 
  density, 
  as 
  distance 
  from 
  the 
  water 
  point 
  increases. 
  

  

  This 
  is 
  notable 
  in 
  the 
  catches 
  on 
  Bugalla 
  Island 
  (Table 
  XVIII), 
  at 
  Dumo 
  Point, 
  

   on 
  Bujaju 
  Peninsula, 
  and 
  on 
  Kitebo 
  Peninsula 
  (Sect. 
  V 
  (e) 
  ). 
  On 
  Bujaju 
  and 
  also 
  on 
  

   Manene 
  Island 
  the 
  male 
  density 
  was 
  greater 
  inland, 
  but 
  the 
  female 
  percentage 
  

   strikingly 
  lower 
  On 
  Bukassa 
  Island 
  male 
  density 
  fell 
  and 
  female 
  percentage 
  

   remained 
  the 
  same, 
  with 
  no 
  serious 
  exception. 
  The 
  Mbugwe 
  hill-top 
  colony 
  is 
  the 
  

   one 
  striking 
  exception, 
  and 
  this 
  is 
  also 
  unique 
  in 
  being, 
  apparently, 
  quite 
  independent 
  

   •of 
  colonies 
  along 
  the 
  shore 
  and 
  entirely 
  different 
  in 
  this 
  respect 
  from 
  the 
  infestations 
  

   at 
  Dumo, 
  Bujaju, 
  Kitebo 
  and 
  on 
  Bugalla 
  Island, 
  which 
  are 
  extensions 
  inland 
  of 
  shore 
  

   colonies. 
  

  

  This 
  same 
  phenomenon 
  has 
  been 
  noted 
  repeatedly 
  at 
  other 
  points 
  on 
  Bugalla 
  

   Island, 
  where 
  collections 
  were 
  made 
  at 
  distances 
  of 
  500 
  to 
  2,000 
  yards 
  inland, 
  and 
  the 
  

   whole 
  series 
  of 
  observations 
  falling 
  into 
  this 
  category 
  stand 
  in 
  the 
  sharpest 
  contrast 
  

   to 
  the 
  rule 
  that 
  applies 
  along 
  shore 
  (so 
  well 
  illustrated 
  by 
  the 
  curves 
  in 
  figure 
  4, 
  p. 
  

   372) 
  that 
  female 
  percentage 
  rises 
  as 
  the 
  distance 
  from 
  the 
  centre 
  of 
  infestation 
  

   increases 
  and 
  male 
  density 
  decreases. 
  And 
  it 
  stands, 
  perhaps 
  as 
  the 
  best 
  bit 
  of 
  

   other 
  than 
  purely 
  empirical 
  evidence, 
  in 
  proof 
  of 
  the 
  effect 
  of 
  food 
  supply 
  or 
  

   •distribution 
  of 
  host 
  animals 
  upon 
  inland 
  range 
  of 
  fly. 
  

  

  The 
  shelter 
  on 
  Bugalla 
  Island, 
  for 
  example, 
  or 
  at 
  Kitebo, 
  is 
  in 
  every 
  respect 
  

   as 
  good 
  and 
  attractive 
  to 
  the 
  flies 
  as 
  on 
  the 
  foreshore. 
  Food 
  is 
  better, 
  and 
  more 
  

   abundant. 
  It 
  is 
  only 
  the 
  protection 
  afforded 
  by 
  the 
  breeding 
  grounds 
  that 
  is 
  

   lacking 
  to 
  make 
  the 
  inland 
  conditions 
  of 
  life 
  entirely 
  favourable. 
  

  

  Table 
  XX. 
  

  

  Mujuzi 
  Colony. 
  

  

  Dispersion 
  forced, 
  by 
  hunger, 
  into 
  an 
  

   intolerable 
  environment. 
  

  

  Kitebo 
  Colony. 
  

  

  Dispersion 
  induced 
  (inland) 
  by 
  superior 
  

   attraction 
  of 
  environment. 
  

  

  Distance 
  of 
  observa- 
  

   tion 
  point 
  from 
  colony 
  

   centre. 
  

  

  Male 
  

   density. 
  

  

  Female 
  

  

  per- 
  

   centage. 
  

  

  Distance 
  of 
  observa- 
  

   tion 
  point 
  from 
  colony 
  

   centre. 
  

  

  Male 
  

   density. 
  

  

  Female 
  

  

  per- 
  

   centage. 
  

  

  yards 
  

   700 
  „ 
  

   1,300 
  „ 
  

   1,700 
  „ 
  

   2,300 
  „ 
  

   2,900 
  „ 
  

  

  98-0 
  

   53-0 
  

   20-5 
  

   19'3 
  

   10-0 
  

   5-0 
  

  

  453 
  

   49-2 
  

   64-0 
  

  

  72-7 
  

   80-8 
  

   88-8 
  

  

  yards 
  

  

  200 
  „ 
  

  

  700 
  „ 
  

   1100 
  „ 
  

   1500 
  „ 
  

  

  44'5 
  

   29-0 
  

   20 
  

   20'0 
  

   G-5 
  

  

  54-3 
  

   49 
  1 
  

   37-5 
  

  

  27-2 
  

   23-5 
  

  

  The 
  fly 
  cannot 
  breed 
  inland, 
  and 
  hold 
  its 
  own 
  numerically, 
  on 
  account 
  of 
  lack 
  

   of 
  good 
  breeding 
  places 
  ; 
  but 
  there 
  is 
  continual 
  inland 
  dispersion 
  of 
  flies 
  from 
  the 
  

   colony 
  centres 
  at 
  the 
  breeding 
  places 
  on 
  the 
  foreshore, 
  induced 
  by 
  relatively 
  better 
  

   or 
  more 
  food 
  and 
  equally 
  attractive 
  shelter. 
  The 
  flies 
  are 
  drawn 
  away 
  from 
  the 
  

  

  