﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  425 
  

  

  fS*B™!? 
  

  

  to 
  potential 
  breeding 
  ground 
  was 
  the 
  average 
  exceeded. 
  At 
  points 
  closely 
  adjacent 
  

   to 
  breeding 
  ground 
  the 
  shore 
  was 
  invariably 
  infested, 
  whatsoever 
  its 
  character 
  — 
  

   whether 
  flat 
  or 
  bold, 
  rocky 
  or 
  marshy 
  or 
  clay 
  bank. 
  At 
  no 
  point 
  exceeding 
  1J 
  

   miles 
  distance 
  from 
  breeding 
  ground 
  did 
  the 
  density 
  exceed 
  1*0. 
  At 
  various 
  points 
  

   no 
  flies 
  were 
  caught 
  in 
  from 
  2 
  to 
  5 
  boy-hours 
  passed 
  there. 
  Absence 
  or 
  scarcity 
  

   of 
  fly 
  away 
  from 
  breeding 
  ground 
  was, 
  like 
  presence 
  of 
  it 
  at 
  points 
  adjacent, 
  in 
  

   no 
  manner 
  affected 
  by 
  the 
  character 
  of 
  the 
  shore, 
  as 
  long 
  as 
  it 
  was 
  devoid 
  of 
  sand 
  

   or 
  gravel 
  deposits. 
  

  

  In 
  brief, 
  the 
  evidence, 
  as 
  far 
  as 
  it 
  went, 
  was 
  entirely 
  confirmatory 
  of 
  the 
  theory 
  

   that 
  on 
  large 
  islands, 
  at 
  least, 
  the 
  fly 
  requires 
  in 
  addition 
  to 
  food 
  and 
  shelter 
  the 
  

   protection 
  provided 
  for 
  its 
  pupae 
  by 
  sand 
  or 
  gravel 
  deposits 
  and 
  by 
  nothing 
  else. 
  

  

  Finally, 
  it 
  was 
  estimated 
  that 
  the 
  clearing 
  of 
  bush 
  or 
  forest 
  from 
  about 
  45 
  acres, 
  

   or 
  roughly 
  1 
  per 
  cent, 
  of 
  the 
  total 
  or 
  4 
  per 
  cent, 
  of 
  the 
  arable 
  area 
  of 
  the 
  island, 
  

   would 
  suffice 
  virtually 
  to 
  exterminate 
  the 
  fly. 
  

  

  The 
  data 
  collected 
  during 
  this 
  bit 
  of 
  survey 
  work 
  are 
  presented 
  in 
  fig. 
  6 
  (p. 
  411). 
  

  

  VII 
  (h). 
  The 
  Foster 
  @f 
  SnsuSarity. 
  

  

  The 
  fly 
  survey 
  of 
  Bugaba 
  Island 
  disclosed 
  the 
  existence 
  of 
  semi-detached 
  colonies 
  

   of 
  flies, 
  centring 
  at 
  or 
  ver,y 
  near 
  to 
  the 
  relatively 
  few 
  and 
  short 
  reaches 
  of 
  shore 
  

   that 
  would 
  serve 
  as 
  breeding 
  grounds. 
  

  

  From 
  these 
  colony 
  centres 
  flies 
  dispersed 
  and 
  infested 
  reaches 
  of 
  shore 
  on 
  either 
  

   side 
  along 
  which 
  it 
  was 
  plain 
  that 
  conditions 
  of 
  life 
  were 
  unfavourable 
  to 
  the 
  existence 
  

   of 
  the 
  species, 
  except 
  as 
  migrants 
  from 
  the 
  better 
  protected 
  colony 
  centres, 
  or 
  centres 
  

   of 
  infestation. 
  

  

  It 
  was 
  very 
  plain 
  that 
  the 
  flies 
  actually 
  living 
  in 
  the 
  zone 
  of 
  dispersion 
  and 
  beyond 
  

   the 
  protected 
  precincts 
  could 
  not 
  perpetuate 
  themselves 
  unless 
  the 
  females 
  returned 
  

   to 
  the 
  breeding 
  grounds 
  with 
  their 
  young. 
  The 
  chances 
  that 
  they 
  may 
  do 
  this 
  are 
  

   best 
  nearest 
  the 
  breeding 
  grounds, 
  and 
  decrease 
  as 
  distance 
  from 
  the 
  breeding 
  grounds 
  

   increases. 
  Unless 
  gifted 
  with 
  a 
  " 
  homing 
  " 
  instinct 
  they 
  are 
  as 
  likely 
  to 
  seek 
  breeding 
  

   grounds 
  in 
  the 
  wrong 
  as 
  in 
  the 
  right 
  direction. 
  There 
  is 
  nothing 
  whatever 
  to 
  indicate 
  

   or 
  suggest 
  that 
  they 
  have 
  any 
  such 
  extraordinary 
  prescience. 
  

  

  On 
  the 
  contrary, 
  the 
  dispersion 
  of 
  fly 
  from 
  centres 
  of 
  infestation 
  in 
  protected 
  precincts 
  

   is 
  shown 
  by 
  the 
  graph 
  of 
  the 
  Bugaba 
  colonies 
  and 
  others, 
  to 
  be 
  not 
  incomparable 
  

   to 
  the 
  dispersion 
  of 
  water 
  welling 
  from 
  a 
  spring 
  in 
  an 
  arid 
  region. 
  At 
  the 
  colony 
  

   centre 
  — 
  i.e., 
  within 
  the 
  protected 
  precincts 
  — 
  the 
  fly 
  is 
  perpetually 
  increasing 
  in 
  

   density, 
  and 
  as 
  perpetually 
  flowing 
  or 
  dispersing 
  outward 
  into 
  unprotected 
  territory, 
  

   where 
  its 
  numbers 
  are 
  perpetually 
  decreasing 
  ; 
  much 
  as 
  water 
  from 
  a 
  desert 
  spring 
  

   is 
  continually 
  dispersing 
  outwards 
  into 
  the 
  arid 
  territory 
  surrounding, 
  and 
  as 
  con- 
  

   tinually 
  being 
  lost 
  by 
  evaporation. 
  There 
  is 
  a 
  perfect 
  natural 
  balance 
  between 
  

   outflow 
  of 
  water 
  and 
  loss 
  through 
  evaporation 
  ; 
  an 
  increased 
  outflow 
  causes 
  more 
  

   humid 
  conditions 
  near 
  the 
  source 
  and 
  extension 
  of 
  the 
  irrigated 
  area, 
  until 
  increased 
  

   evaporation 
  compensates, 
  and 
  vice 
  versa. 
  

  

  It 
  is 
  much 
  the 
  same 
  with 
  fly. 
  An 
  increased 
  amount 
  or 
  degree 
  of 
  protection 
  at 
  

   the 
  colony 
  centre, 
  or 
  anything 
  else 
  which 
  is 
  conducive 
  to 
  increased 
  rate 
  of 
  

  

  