﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  357 
  

  

  This 
  strange 
  increase 
  in 
  the 
  activity 
  of 
  the 
  female 
  flies 
  on 
  this 
  islet 
  was 
  obviously 
  

   associated 
  with 
  the 
  experiment 
  being 
  conducted 
  there, 
  and 
  that 
  which 
  seemed 
  the 
  

   most 
  plausible 
  explanation 
  was 
  that 
  the 
  male 
  flies 
  are 
  normally 
  active 
  and 
  easily 
  

   caught 
  at 
  all 
  times 
  during 
  good 
  weather, 
  whether 
  they 
  are 
  hungry 
  or 
  not, 
  but 
  that 
  

   ~the 
  females 
  are 
  normally 
  inactive 
  and 
  not 
  to 
  be 
  caught 
  except 
  when 
  hungry 
  and 
  

   seeking 
  food. 
  This 
  hypothesis 
  was 
  borne 
  out 
  by 
  the 
  observation 
  (made 
  during 
  the 
  

   course 
  of 
  the 
  experiment) 
  that 
  the 
  mere 
  presence 
  of 
  the 
  corps 
  of 
  fly 
  boys 
  (9 
  or 
  10 
  of 
  

   them) 
  on 
  the 
  islet 
  had 
  temporarily 
  banished 
  from 
  it 
  the 
  several 
  crocodiles 
  and 
  Varanus 
  

   which 
  had 
  formerly 
  frequented 
  it 
  and 
  which 
  were 
  the 
  only 
  visible 
  sources 
  of 
  food 
  

   for 
  the 
  flies. 
  Assuming 
  that 
  only 
  hungry 
  females 
  are 
  active 
  and 
  easily 
  caught, 
  

   the 
  effect 
  of 
  this 
  would 
  be 
  to 
  increase 
  the 
  number 
  of 
  them 
  and 
  therefore 
  the 
  number 
  

   caught 
  per 
  boy 
  per 
  hour, 
  through 
  decreasing 
  their 
  food 
  supply. 
  

  

  On 
  this 
  hypothesis 
  such 
  variations 
  in 
  the 
  percentage 
  of 
  females 
  amongst 
  caught 
  

   flies 
  as 
  are 
  presented 
  in 
  Tables 
  I 
  and 
  II 
  (i.e., 
  such 
  as 
  occur 
  between 
  different 
  islands) 
  

   would 
  indicate 
  corresponding 
  variations 
  in 
  abundance 
  of 
  food, 
  or 
  density 
  of 
  host 
  

   animals. 
  It 
  was 
  resolved 
  to 
  test 
  this 
  hypothesis 
  by 
  banishing 
  the 
  host 
  animals 
  

   from 
  a 
  small 
  islet 
  without 
  catching 
  off 
  any 
  of 
  the 
  flies, 
  and 
  observing 
  the 
  effect 
  on 
  

   sex 
  ratio. 
  

  

  This 
  experiment 
  was 
  made 
  on 
  the 
  small 
  island 
  of 
  Lugazi, 
  in 
  the 
  following 
  manner 
  

   and 
  with 
  the 
  following 
  results. 
  

  

  19th 
  and 
  20th 
  December 
  1913. 
  A 
  total 
  of 
  197 
  flies 
  were 
  caught 
  on 
  the 
  islet, 
  the 
  

   sex 
  was 
  determined 
  and 
  they 
  were 
  then 
  liberated 
  (in 
  order 
  that 
  catching 
  off 
  of 
  males 
  

   should 
  not 
  affect 
  the 
  sex 
  ratio). 
  The 
  ratio 
  was, 
  males 
  : 
  females 
  : 
  : 
  166 
  : 
  31 
  = 
  15*5 
  

   per 
  cent, 
  females. 
  

  

  22nd 
  to 
  27th 
  December 
  1913. 
  All 
  host 
  animals 
  known 
  to 
  be 
  fed 
  upon 
  by 
  Glossina, 
  

   consisting 
  of 
  several 
  Varanus 
  and 
  crocodiles, 
  were 
  systematically 
  hunted 
  from 
  the 
  

   islet. 
  

  

  26th 
  and 
  27th 
  December 
  1913. 
  A 
  total 
  of 
  208 
  flies 
  were 
  caught, 
  showing 
  sex 
  

   ratio, 
  males 
  : 
  females 
  : 
  : 
  89 
  : 
  119 
  = 
  57*2 
  per 
  cent, 
  females. 
  

  

  This 
  experiment 
  was 
  carefully 
  conducted, 
  and 
  careful 
  notes 
  were 
  kept 
  upon 
  the 
  

   behaviour 
  of 
  the 
  flies 
  on 
  the 
  islet 
  towards 
  man 
  and 
  also 
  towards 
  certain 
  domestic 
  

   .animals 
  which 
  were 
  tethered 
  there 
  (see 
  Sect. 
  II 
  (6)). 
  They 
  were 
  so 
  strikingly 
  affected 
  

   by 
  the 
  banishment 
  of 
  their 
  reptilian 
  hosts 
  as 
  to 
  leave 
  no 
  doubt 
  that 
  they 
  had 
  been 
  

   principally 
  dependent 
  on 
  them, 
  and 
  that 
  the 
  increase 
  in 
  percentage 
  of 
  females 
  from 
  

   15*5 
  to 
  57*2 
  was 
  the 
  direct 
  result 
  of 
  food 
  shortage. 
  Data 
  on 
  this 
  phase 
  of 
  the 
  

   experiment 
  appear 
  in 
  Sect. 
  II 
  following. 
  

  

  I 
  (d). 
  The 
  Real 
  Ratio 
  between 
  the 
  Sexes 
  of 
  Glossina 
  palpalis. 
  

  

  The 
  foregoing 
  observations 
  and 
  experiments 
  demonstrate 
  conclusively 
  enough 
  

   that 
  the 
  ratio 
  between 
  the 
  sexes 
  of 
  caught 
  flies 
  is 
  no 
  criterion 
  of 
  the 
  real 
  sex 
  ratio 
  

   in 
  the 
  locality 
  where 
  the 
  catch 
  is 
  made. 
  It 
  would 
  be 
  impossible 
  to 
  determine 
  the 
  

   real 
  ratio 
  accurately, 
  otherwise 
  than 
  by 
  the 
  continuation 
  of 
  such 
  an 
  experiment 
  

   as 
  was 
  made 
  on 
  Lula 
  until 
  all 
  flies 
  had 
  been 
  caught, 
  and 
  this 
  would 
  require 
  more 
  

   time 
  than 
  the 
  knowledge 
  is 
  likely 
  to 
  be 
  worth. 
  

  

  