﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  421 
  

  

  In 
  one 
  case 
  what 
  had 
  been 
  two 
  small 
  islands 
  lying 
  of! 
  the 
  shore 
  of 
  a 
  larger 
  one 
  had 
  

   been 
  united 
  by 
  a 
  low 
  isthmus, 
  and 
  were 
  connected 
  with 
  the 
  larger 
  island 
  by 
  an 
  almost 
  

   continuous 
  line 
  of 
  " 
  merinde 
  " 
  or 
  ambatch 
  trees 
  growing 
  in 
  the 
  shallowed 
  water. 
  

  

  Many 
  other 
  radical 
  changes 
  in 
  the 
  character 
  of 
  the 
  shore 
  line 
  were 
  noted, 
  and 
  it 
  

   soon 
  became 
  evident 
  that 
  although 
  the 
  fly 
  was 
  to 
  be 
  found 
  in 
  maximum 
  density 
  along 
  

   the 
  open 
  fly 
  beaches, 
  the 
  great 
  mass 
  or 
  body 
  of 
  fly 
  bred 
  in 
  the 
  deposits 
  of 
  sand 
  and 
  

   gravel 
  marking 
  the 
  old 
  beach 
  line, 
  usually 
  hidden 
  from 
  sight. 
  

  

  Moreover 
  in 
  not 
  a 
  few 
  cases 
  it 
  appeared 
  certain 
  that 
  with 
  the 
  recession 
  of 
  the 
  lake 
  

   conditions 
  of 
  life 
  formerly 
  intolerable 
  for 
  tsetse 
  had 
  become 
  favourable 
  to 
  it 
  in 
  many 
  

   localities, 
  and 
  that 
  in 
  other 
  localities 
  the 
  effect 
  had 
  been 
  the 
  opposite. 
  

  

  The 
  question 
  of 
  lake 
  level, 
  and 
  of 
  fluctuations 
  of 
  it, 
  was 
  thus 
  injected 
  into 
  the 
  

   general 
  subj 
  ect 
  of 
  tsetse 
  bionomics 
  as 
  one 
  of 
  its 
  more 
  important 
  phases. 
  Data 
  were 
  

   sought, 
  and 
  it 
  was 
  discovered 
  that 
  the 
  old 
  beach 
  line 
  marked 
  the 
  high 
  lake-level 
  

   of 
  1906 
  ; 
  that 
  the 
  existing 
  low 
  level 
  was 
  likely 
  to 
  be 
  only 
  temporary 
  ; 
  and 
  that 
  at 
  

   any 
  time 
  the 
  waters 
  might 
  rise 
  to 
  the 
  old 
  level. 
  

  

  In 
  consequence 
  great 
  changes 
  and 
  fluctuations 
  in 
  density 
  of 
  tsetse 
  might 
  be 
  expected 
  

   to 
  occur 
  without 
  other 
  warning 
  than 
  rise 
  or 
  fall 
  of 
  the 
  water. 
  Eventually, 
  in 
  comparing 
  

   conditions 
  on 
  a 
  certain 
  reach 
  of 
  shore 
  as 
  they 
  existed 
  in 
  1915, 
  with 
  conditions 
  as 
  they 
  

   had 
  been 
  specifically 
  described 
  in 
  old 
  reports 
  of 
  the 
  officers 
  employed 
  on 
  Sleeping 
  

   Sickness 
  Extended 
  Investigations 
  in 
  1906, 
  it 
  was 
  found 
  that 
  changes 
  in 
  the 
  degree 
  

   of 
  infestation 
  had 
  been 
  of 
  the 
  most 
  extreme 
  character. 
  The 
  Mujuzi 
  colony, 
  for 
  

   the 
  most 
  striking 
  example, 
  already 
  mentioned 
  several 
  times, 
  and 
  last 
  cited 
  in 
  Table 
  

   XXXI 
  just 
  preceding, 
  was 
  non-existent 
  in 
  1906. 
  

  

  A 
  more 
  detailed 
  account 
  of 
  the 
  changes 
  wrought 
  in 
  specific 
  cases 
  is 
  presented 
  in 
  

   Sect, 
  XL 
  

  

  In 
  certain 
  respects 
  no 
  factor 
  in 
  the 
  bionomics 
  of 
  Glossina 
  palpalis 
  in 
  this 
  region 
  

   is 
  more 
  important 
  than 
  this 
  of 
  the 
  fluctuations 
  in 
  lake 
  level, 
  as 
  the 
  breeding 
  places 
  

   of 
  the 
  insect 
  are 
  affected. 
  The 
  rising 
  waters 
  uproot 
  vegetation, 
  clear 
  the 
  shore, 
  

   and 
  wash 
  clean 
  the 
  beaches. 
  Falling 
  waters 
  leave 
  ideal 
  conditions 
  of 
  life 
  for 
  tsetse 
  

   where 
  formerly 
  they 
  were 
  hard 
  or 
  intolerable. 
  Then 
  the 
  rapidly 
  growing, 
  tropical 
  

   vegetation 
  closes 
  in 
  on 
  the 
  breeding 
  places, 
  gradually 
  shutting 
  them 
  off 
  from 
  the 
  

   flies, 
  until 
  rising 
  waters 
  shall 
  again 
  open 
  them 
  to 
  occupation. 
  

  

  VII 
  (/). 
  Correlation 
  between 
  Extent 
  and 
  Character 
  of 
  Breeding 
  Grounds 
  and 
  

   Degree 
  of 
  Infestation 
  of 
  small 
  islets 
  by 
  Glossina 
  palpalis. 
  

   A 
  fly 
  survey 
  of 
  small 
  islets 
  of 
  less 
  than 
  one 
  square 
  mile 
  in 
  Victoria 
  Nyanza 
  was 
  

   begun 
  in 
  December 
  1913 
  and 
  continued 
  through 
  parts 
  of 
  January, 
  February, 
  August 
  

   and 
  September 
  following. 
  The 
  object 
  was 
  to 
  ascertain 
  the 
  extent 
  to 
  which 
  the 
  degree 
  

   of 
  infestation 
  is 
  correlated 
  with 
  amount 
  and 
  character 
  of 
  breeding 
  grounds 
  as 
  

   represented 
  by 
  deposits 
  of 
  beach 
  sand 
  or 
  gravel 
  along 
  either 
  the 
  old 
  or 
  new 
  beach 
  

   line. 
  First 
  and 
  last, 
  some 
  50 
  islets 
  were 
  visited. 
  Conditions 
  with 
  respect 
  to 
  extent 
  

   and 
  character 
  of 
  breeding 
  grounds 
  were 
  extremely 
  diverse. 
  On 
  some 
  islets 
  no 
  deposits 
  

   of 
  beach 
  sand 
  or 
  gravel 
  could 
  be 
  found 
  — 
  on 
  others 
  they 
  were 
  numerous 
  and 
  extensive. 
  

   The 
  islets 
  may 
  be 
  roughly 
  assigned 
  to 
  five 
  categories, 
  accordingly 
  as 
  breeding 
  grounds 
  

   of 
  this 
  type 
  are 
  " 
  very 
  good," 
  " 
  good," 
  " 
  poor," 
  " 
  very 
  poor" 
  or 
  " 
  none," 
  and 
  the 
  

   accompanying 
  table 
  (Table 
  XXXII) 
  has 
  been 
  framed 
  to 
  include 
  a 
  fairly 
  represen- 
  

   tative 
  number 
  from 
  each 
  group. 
  

  

  