﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  359 
  

  

  II 
  (a). 
  Methods 
  used 
  for 
  Estimating 
  the 
  Density 
  and 
  Economic 
  Status 
  of 
  Glossina 
  

   palpalis. 
  

  

  The 
  most 
  convenient 
  method 
  for 
  measuring 
  variations 
  in 
  the 
  density 
  of 
  Glossina 
  

   palpalis 
  is 
  that 
  of 
  employing 
  expert 
  " 
  fly 
  boys 
  " 
  and 
  of 
  counting 
  the 
  number 
  of 
  

   flies 
  which 
  can 
  be 
  caught 
  per 
  boy 
  per 
  hour 
  under 
  standardised 
  conditions. 
  This 
  

   method 
  had 
  already 
  been 
  used 
  by 
  Dr. 
  G. 
  D. 
  H. 
  Carpenter 
  and 
  others, 
  and 
  when 
  

   care 
  was 
  taken 
  to 
  eliminate 
  sources 
  of 
  error 
  very 
  reliable 
  figures 
  were 
  secured.* 
  

  

  On 
  account 
  of 
  the 
  very 
  variable 
  activity 
  of 
  the 
  females 
  it 
  is 
  obvious 
  that 
  estimates 
  

   of 
  local 
  density 
  must 
  be 
  based 
  on 
  the 
  catch 
  of 
  males. 
  That 
  of 
  females 
  is 
  of 
  little 
  

   significance 
  by 
  itself 
  in 
  indicating 
  density, 
  but 
  taken 
  in 
  connection 
  with 
  the 
  catch 
  

   of 
  males 
  it 
  possesses 
  a 
  large 
  significance, 
  and 
  is 
  indicative 
  of 
  variations 
  in 
  the 
  

   economic 
  status 
  of 
  the 
  fly. 
  This, 
  like 
  density, 
  varies 
  extremely 
  (a) 
  from 
  time 
  to 
  

   time 
  in 
  the 
  same 
  region 
  or 
  locality, 
  and 
  (6) 
  from 
  one 
  district 
  or 
  locality 
  to 
  another 
  

   at 
  the 
  same 
  time. 
  It 
  is 
  in 
  part 
  determined 
  by 
  the 
  density 
  of 
  fly, 
  and 
  variations 
  

   in 
  density 
  correspond 
  to 
  variations 
  in 
  economic 
  status 
  (i.e., 
  by 
  reducing 
  density 
  

   we 
  assume 
  that 
  we 
  depreciate 
  the 
  injurious 
  status 
  of 
  the 
  insect, 
  and 
  its 
  status 
  must 
  

   naturally 
  vary 
  with 
  natural 
  fluctuations 
  in 
  density) 
  ; 
  but 
  in 
  larger 
  part 
  it 
  is 
  

   determined 
  by 
  the 
  behaviour 
  of 
  the 
  fly 
  towards 
  man, 
  and 
  this 
  in 
  turn 
  by 
  abundance 
  

   of 
  wild 
  hosts. 
  The 
  female 
  percentage 
  is 
  an 
  index 
  to 
  abundance 
  of 
  hosts, 
  and 
  therefore 
  

   to 
  the 
  liability 
  of 
  man 
  to 
  attack. 
  

  

  To 
  illustrate 
  the 
  above, 
  two 
  extremes 
  cited 
  in 
  Table 
  III 
  may 
  be 
  used 
  : 
  the 
  

   infestations 
  as 
  measured 
  in 
  Bugaba 
  and 
  Bale 
  beaches 
  respectively. 
  In 
  each 
  case 
  

   the 
  actual 
  catches 
  of 
  fly 
  were 
  made 
  at 
  three 
  points 
  a 
  few 
  hundred 
  yards 
  apart 
  on 
  

   these 
  beaches, 
  and 
  the 
  complete 
  data 
  concerning 
  degree 
  of 
  infestation 
  are 
  presented 
  

   in 
  Table 
  VIII. 
  

  

  At 
  first 
  glance, 
  in 
  comparing 
  the 
  density 
  of 
  fly 
  at 
  these 
  two 
  points 
  on 
  the 
  basis 
  

   of 
  the 
  total 
  catch 
  — 
  both 
  sexes 
  — 
  per 
  boy 
  per 
  hour, 
  it 
  would 
  appear 
  that 
  there 
  were 
  

   twice 
  as 
  many 
  flies 
  along 
  the 
  Bale 
  as 
  along 
  the 
  Bugaba 
  beach, 
  for 
  the 
  total 
  catch 
  

   is 
  more 
  than 
  twice 
  as 
  great. 
  But 
  the 
  difference 
  is 
  very 
  largely 
  due 
  to 
  the 
  enormously 
  

   greater 
  activity 
  of 
  the 
  females 
  at 
  Bale, 
  and 
  if 
  allowance 
  is 
  made 
  for 
  as 
  many, 
  

   proportionately 
  to 
  the 
  males, 
  at 
  Bugaba 
  as 
  at 
  Bale, 
  it 
  appears 
  that 
  there 
  are 
  almost 
  

   three 
  times 
  as 
  many 
  fly 
  at 
  Bugaba, 
  instead 
  of 
  less 
  than 
  half 
  as 
  many. 
  

  

  * 
  Proper 
  attention 
  to 
  the 
  following 
  suggestions 
  will 
  serve 
  to 
  eliminate 
  various 
  possibilities 
  

   of 
  error 
  : 
  — 
  

  

  (1) 
  Boys 
  should 
  be 
  trained 
  at 
  least 
  one 
  month 
  ; 
  all 
  new 
  boys 
  in 
  a 
  corps 
  without 
  one 
  or 
  

   or 
  two 
  experts 
  as 
  teachers 
  would 
  require 
  longer 
  training. 
  

  

  (2) 
  Nets 
  must 
  have 
  a 
  standard-sized 
  ring 
  and 
  a 
  standard 
  length 
  of 
  handle; 
  an 
  8-inch 
  

   ring 
  and 
  18 
  -inch 
  handle 
  were 
  used. 
  

  

  (3) 
  Catches 
  should 
  not 
  be 
  made 
  before 
  8.30 
  or 
  9 
  a.m. 
  nor 
  later 
  than 
  2.30 
  or 
  3 
  p.m. 
  

  

  (4) 
  Boys 
  will 
  make 
  more 
  even 
  catches 
  if 
  provided 
  each 
  with 
  a 
  dark- 
  coloured 
  umbrella, 
  

   upon 
  which 
  the 
  flies 
  will 
  settle, 
  and 
  from 
  which 
  they 
  are 
  easily 
  caught. 
  

  

  (5) 
  Unless 
  density 
  is 
  very 
  low 
  — 
  less 
  than 
  1*0 
  — 
  it 
  is 
  better 
  not 
  to 
  spend 
  more 
  than 
  

   2 
  to 
  3 
  "boy 
  hours" 
  at 
  the 
  same 
  point 
  on 
  the 
  same 
  day; 
  density 
  is 
  easily 
  reduced, 
  

   temporarily, 
  by 
  catching. 
  

  

  _ 
  (6) 
  Boys 
  should 
  be 
  stationed 
  along 
  the 
  routes 
  most 
  likely 
  to 
  be 
  followed 
  by 
  moving 
  

   flies, 
  and 
  always, 
  if 
  there 
  is 
  shadow, 
  at 
  the 
  edge 
  of 
  it. 
  

  

  (7) 
  Estimates 
  of 
  density 
  must 
  be 
  based 
  on 
  catch 
  of 
  males, 
  on 
  account 
  of 
  the 
  variability 
  

   of 
  female 
  activity. 
  

  

  (8) 
  Good 
  results 
  cannot 
  be 
  secured 
  on 
  cool, 
  cloudy 
  or 
  windy 
  days. 
  

  

  