﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  449 
  

  

  The 
  dependence 
  of 
  Glossina 
  palpalis 
  upon 
  specific 
  forms 
  of 
  protection 
  — 
  breeding 
  

   grounds 
  and 
  shelter 
  — 
  has 
  been 
  shown 
  in 
  Sects. 
  VII 
  and 
  VIII. 
  Except 
  when 
  provided 
  

   with 
  both 
  kinds 
  within 
  easy 
  reach 
  (of 
  the 
  flies) 
  from 
  each 
  other 
  the 
  species 
  cannot 
  

   exist. 
  Where 
  both 
  kinds 
  occur 
  in 
  sufficient 
  proximity 
  the 
  fly 
  can 
  exist 
  if 
  also 
  

   provided 
  with 
  food, 
  but 
  food, 
  also, 
  must 
  be 
  within 
  easy 
  reach 
  of 
  flies 
  from 
  both 
  

   kinds 
  of 
  protection. 
  

  

  It 
  is 
  this 
  factor 
  of 
  the 
  actual 
  location 
  of 
  food 
  with 
  respect 
  to 
  protection 
  that 
  

   counts 
  most 
  heavily 
  in 
  determining 
  the 
  range 
  and 
  density 
  of 
  fly. 
  It 
  is 
  much 
  less 
  

   a 
  question 
  how 
  much 
  food 
  — 
  how 
  many 
  host 
  animals 
  — 
  exists 
  in 
  a 
  given 
  region 
  or 
  

   district, 
  or 
  on 
  a 
  given 
  island, 
  than 
  it 
  is 
  one 
  of 
  the 
  quantity 
  of 
  food 
  or 
  number 
  of 
  

   host 
  animals 
  existing 
  in 
  the 
  adequately 
  protected 
  precincts. 
  It 
  is 
  not 
  necessary 
  

   that 
  the 
  host 
  animals 
  shall 
  be 
  destroyed 
  in 
  order 
  to 
  injure 
  the 
  fly 
  ; 
  but 
  is 
  quite 
  

   sufficient 
  that 
  they 
  should 
  move 
  a 
  little 
  outside 
  the 
  range 
  or 
  reach 
  of 
  flies 
  from 
  

   either 
  shelter 
  or 
  breeding 
  places. 
  

  

  Therefore 
  if 
  the 
  animal 
  is 
  induced 
  by 
  Tabanus, 
  or 
  any 
  other 
  biting 
  fly, 
  to 
  move 
  

   a 
  little 
  farther 
  away 
  from 
  the 
  specifically 
  protected 
  precincts, 
  Glossina 
  is 
  forced 
  

   to 
  follow, 
  and 
  in 
  following 
  is 
  exposed 
  to 
  all 
  the 
  risks, 
  and 
  enemies 
  of 
  a 
  destructive 
  

   nature, 
  that 
  make 
  specific 
  protection 
  a 
  requisite 
  for 
  its 
  existence. 
  The 
  effect 
  of 
  the 
  

   rival 
  is 
  precisely 
  equivalent 
  to 
  either 
  of 
  the 
  following 
  : 
  — 
  (a) 
  reduction 
  in 
  quantity 
  

   of 
  available 
  food, 
  (b) 
  reduction 
  in 
  quantity 
  or 
  degree 
  of 
  protection, 
  or 
  (c) 
  increase 
  

   in 
  number 
  or 
  destructiveness 
  of 
  enemies. 
  

  

  This 
  is 
  if 
  the 
  host 
  is 
  induced 
  to 
  leave 
  the 
  locality. 
  It 
  is 
  the 
  same 
  if 
  retaliatory 
  

   activities 
  on 
  the 
  part 
  of 
  the 
  host 
  induce 
  the 
  flies 
  to 
  desist 
  from 
  attack 
  and 
  to 
  move 
  

   on 
  in 
  search 
  of 
  another, 
  more 
  submissive 
  animal. 
  To 
  do 
  this 
  the 
  flies 
  must 
  leave 
  

   protected 
  precincts 
  and 
  undergo 
  greater 
  risk 
  of 
  being 
  destroyed 
  themselves, 
  or 
  of 
  

   being 
  unable 
  to 
  find 
  protection 
  for 
  their 
  young. 
  

  

  The 
  activities 
  of 
  Tabanus 
  have 
  the 
  direct 
  effect 
  of 
  reducing 
  the 
  quantity 
  of 
  available 
  

   food 
  in 
  protected 
  precincts, 
  which 
  is 
  the 
  equivalent 
  of 
  either 
  reducing 
  the 
  amount 
  

   of 
  degree 
  of 
  protection, 
  or 
  increasing 
  the 
  number 
  or 
  destructiveness 
  of 
  enemies. 
  

  

  IX 
  (h). 
  Super-density 
  Of 
  Glossina 
  palpalis. 
  

  

  There 
  appears 
  to 
  be 
  nothing 
  to 
  prevent 
  the 
  multiplication 
  of 
  Glossina 
  palpalis 
  

   to 
  any 
  degree 
  of 
  density 
  which 
  the 
  food 
  supply 
  permits 
  in 
  any 
  locality 
  where 
  protec- 
  

   tion 
  is 
  provided 
  for 
  it, 
  except 
  the 
  continued 
  dispersion 
  of 
  flies 
  outwards 
  from 
  the 
  

   protected 
  precincts 
  to 
  infest 
  a 
  surrounding 
  zone 
  of 
  unprotected 
  territory. 
  Within 
  

   the 
  protected 
  precincts 
  the 
  natural 
  increase 
  of 
  the 
  species 
  is 
  greater 
  than 
  the 
  

   mortality, 
  but 
  gain 
  through 
  natural 
  increase 
  is 
  equal 
  to 
  loss 
  through 
  mortality 
  

   plus 
  loss 
  through 
  dispersion. 
  Hence 
  density 
  does 
  not 
  increase 
  beyond 
  certain 
  limits, 
  

   because 
  when 
  the 
  flies 
  become 
  sufficiently 
  numerous 
  to 
  arouse 
  their 
  host 
  animals 
  

   to 
  the 
  point 
  of 
  retaliation, 
  the 
  immediate 
  effect 
  is 
  to 
  accelerate 
  dispersion, 
  thus 
  

   reducing 
  density 
  in 
  the 
  protective 
  precincts. 
  Outside 
  these 
  precincts 
  mortality 
  

   is 
  greater 
  than 
  reproduction, 
  but 
  loss 
  through 
  mortality 
  is 
  equal 
  to 
  gain 
  through 
  

   natural 
  increase 
  . 
  plus 
  gain 
  through 
  immigration. 
  

  

  