﻿456 
  W. 
  F. 
  FISKE. 
  

  

  relatively 
  little 
  difficulty 
  in 
  feeding 
  ; 
  but 
  if 
  there 
  are 
  very 
  many 
  flies, 
  the 
  man 
  

   provides 
  himself 
  with 
  one 
  or 
  two 
  fly 
  switches, 
  and 
  they 
  have 
  proportionately 
  greater 
  

   difficulty 
  in 
  feeding. 
  

  

  Availability 
  of 
  food 
  is 
  also 
  measured 
  by 
  the 
  precise 
  location 
  of 
  host 
  animals 
  with 
  

   respect 
  to 
  protection. 
  If 
  separated 
  from 
  shelter 
  by 
  as 
  much 
  as 
  20 
  yards 
  of 
  unsheltered 
  

   terrain, 
  food 
  may 
  be 
  entirely 
  unavailable 
  to 
  the 
  flies. 
  This 
  was 
  proved 
  by 
  conditions 
  

   along 
  certain 
  reaches 
  of 
  shore 
  in 
  Buddu, 
  where 
  there 
  was 
  abundance 
  of 
  crocodiles 
  

   along 
  a 
  sandy 
  beach 
  separated 
  by 
  from 
  20 
  to 
  100 
  yards 
  of 
  grass 
  land 
  from 
  shelter 
  and 
  

   breeding 
  grounds. 
  The 
  flies 
  could 
  not 
  perceive 
  the 
  hosts 
  at 
  this 
  distance, 
  and 
  they 
  

   do 
  not 
  freely 
  range 
  so 
  far 
  from 
  shelter 
  in 
  search 
  of 
  food. 
  

  

  The 
  factors 
  which 
  operate 
  naturally 
  and 
  control 
  the 
  range 
  and 
  density 
  of 
  Glossina 
  

   "palpalis 
  in 
  this 
  region 
  are, 
  mainly, 
  as 
  described 
  above 
  ; 
  the 
  factors 
  which 
  can 
  be 
  

   operated 
  by 
  human 
  effort 
  to 
  reduce 
  obnoxious 
  density 
  to 
  within 
  innocuous 
  limits 
  

   are 
  identical. 
  It 
  is 
  useless 
  to 
  contemplate 
  destructive 
  control 
  measures. 
  We 
  can 
  

   see 
  from 
  the 
  experiment 
  and 
  observations 
  made 
  on 
  the 
  " 
  spider 
  islands" 
  that 
  it 
  

   requires 
  an 
  immense 
  amount 
  of 
  destruction 
  by 
  specific 
  agency 
  to 
  produce 
  a 
  

   measurable 
  effect 
  on 
  the 
  density 
  of 
  the 
  species. 
  The 
  spiders 
  on 
  Wema 
  Island 
  actually 
  

   destroyed 
  enormous 
  numbers 
  of 
  flies, 
  but 
  for 
  the 
  most 
  part 
  these 
  flies 
  would 
  have 
  

   been 
  as 
  promptly 
  destroyed 
  by 
  any 
  one 
  of 
  various 
  other 
  agencies 
  in 
  the 
  absence 
  

   of 
  ihe 
  spiders. 
  If 
  the 
  spiders 
  are 
  about, 
  the 
  flies 
  increase 
  to 
  slightly 
  greater 
  density, 
  

   and 
  then, 
  through 
  wider 
  dispersion, 
  run 
  greater 
  risks 
  and 
  the 
  natural 
  balance 
  is 
  

   struck 
  at 
  a 
  slightly 
  higher 
  level. 
  Or, 
  stating 
  the 
  same 
  truth 
  in 
  another 
  way, 
  the 
  main 
  

   effect 
  of 
  artificial 
  or 
  unduly 
  heavy 
  natural 
  destruction 
  of 
  flies 
  by 
  any 
  specific 
  agency 
  

   isjto 
  make 
  conditions 
  of 
  life 
  much 
  more 
  favourable 
  to 
  the 
  rapid 
  multiplication 
  of 
  the 
  

   survivors. 
  It 
  is 
  wholly 
  impractical 
  to 
  consider 
  any 
  control 
  measures 
  involving 
  

   artificial 
  destruction 
  of 
  flies, 
  and 
  wholly 
  necessary 
  to 
  rely 
  upon 
  measures 
  designed 
  to 
  

   deprive 
  the 
  insects 
  of 
  either 
  food 
  or 
  protection 
  or 
  to 
  render 
  food 
  less 
  available 
  to 
  them. 
  

  

  For 
  reasons 
  in 
  part 
  set 
  forth 
  in 
  Sect. 
  II 
  preceding 
  it 
  is 
  regarded 
  as 
  inadvisable 
  

   and 
  even 
  dangerous 
  to 
  contemplate 
  control 
  of 
  the 
  pest 
  through 
  depriving 
  it 
  of 
  food. 
  

   It 
  is 
  probable 
  that 
  if 
  completely 
  deprived 
  of 
  all 
  favoured 
  hosts 
  it 
  would 
  be 
  unable 
  to 
  

   exist 
  on 
  hosts 
  favoured 
  to 
  a 
  no 
  greater 
  degree 
  than 
  sheep, 
  goats 
  and 
  man, 
  but 
  it 
  is 
  

   probable 
  that 
  it 
  would 
  continue 
  to 
  exist 
  if 
  cattle 
  or 
  pigs 
  were 
  provided. 
  It 
  is 
  also 
  

   certain 
  that 
  where 
  favoured 
  hosts 
  are 
  plentiful, 
  man 
  is 
  almost 
  immune 
  to 
  attack, 
  but 
  

   that 
  when 
  they 
  are 
  few 
  man 
  is 
  freely 
  attacked, 
  and 
  our 
  object 
  must 
  always 
  be 
  to 
  

   protect 
  man 
  rather 
  than 
  to 
  destroy 
  flies. 
  

  

  There 
  is 
  ro 
  such 
  objection 
  to 
  the 
  proposition 
  of 
  controlling 
  fly 
  through 
  depriving 
  

   it 
  of 
  protection, 
  and 
  it 
  is 
  on 
  measures 
  designed 
  to 
  this 
  end 
  that 
  we 
  must 
  chiefly 
  

   rely. 
  They 
  are 
  the 
  clearing 
  measures 
  already 
  in 
  use, 
  and 
  they 
  have 
  been 
  proved 
  

   efficacious 
  on 
  many 
  occasions. 
  The 
  maximum 
  of 
  economy 
  and 
  efficiency 
  is 
  to 
  be 
  

   gained 
  through 
  clearing 
  at 
  precisely 
  the 
  right 
  points 
  — 
  i.e., 
  at 
  the 
  centres 
  of 
  infestation 
  

   wherein 
  natural 
  increase 
  of 
  fly 
  is 
  most 
  rapid. 
  By 
  clearing 
  these 
  the 
  dispersion 
  of 
  flies 
  

   into 
  the 
  surrounding 
  zone 
  is 
  prevented, 
  and 
  the 
  effect 
  is 
  general. 
  By 
  clearing 
  in 
  

   the 
  zone 
  infested 
  by 
  immigrating 
  flies 
  the 
  effect 
  is 
  local 
  at 
  best. 
  A 
  small 
  amount 
  of 
  

   clearing 
  at 
  the 
  centres 
  of 
  infestation 
  may 
  be 
  much 
  more 
  effective 
  than 
  a 
  large 
  

   amount 
  of 
  clearing 
  away 
  from 
  them. 
  

  

  