﻿80 
  RUPERT 
  W. 
  JACK. 
  

  

  a 
  questionable 
  premise, 
  namely, 
  that 
  the 
  distribution 
  of 
  the 
  fly 
  is 
  the 
  same 
  in 
  both 
  

   wet 
  and 
  dry 
  seasons. 
  If 
  this 
  is 
  the 
  case 
  in 
  the 
  locality 
  where 
  the 
  observations 
  were 
  

   made, 
  the 
  results 
  obtained 
  have 
  great 
  value 
  ; 
  but 
  it 
  is 
  certainly 
  not 
  the 
  case 
  in 
  

   Southern 
  Rhodesia, 
  nor, 
  according 
  to 
  Lamborn, 
  in 
  Nyasaland. 
  The 
  vast 
  bulk 
  of 
  the 
  

   forest 
  in 
  this 
  territory 
  consists 
  of 
  some 
  three 
  species 
  of 
  Brachystegia, 
  producing 
  the 
  

   type 
  of 
  forest 
  known 
  to 
  the 
  Matabele 
  as 
  " 
  gusu," 
  and 
  the 
  well-known 
  mopani. 
  The 
  

   habit 
  of 
  " 
  gusu 
  " 
  forest 
  varies 
  with 
  the 
  soil 
  and 
  subterranean 
  water-supply. 
  Broadly 
  

   speaking, 
  the 
  trees 
  concerned 
  appear 
  to 
  become 
  leafless 
  all 
  over 
  the 
  territory 
  at 
  

   about 
  the 
  same 
  time 
  of 
  year, 
  namely 
  late 
  in 
  July. 
  In 
  many 
  places, 
  as 
  at 
  Salisbury, 
  

   the 
  new 
  leaves 
  appear 
  again 
  almost 
  immediately, 
  and 
  if 
  this 
  were 
  the 
  case 
  everywhere, 
  

   it 
  is 
  to 
  be 
  presumed 
  that 
  no 
  marked 
  seasonal 
  change 
  in 
  the 
  distribution 
  of 
  fly 
  in 
  

   gusu 
  country 
  would 
  take 
  place. 
  In 
  all 
  the 
  fly 
  country 
  known 
  to 
  the 
  writer, 
  however, 
  

   the 
  forest 
  does 
  not 
  as 
  a 
  rule 
  come 
  into 
  leaf 
  again 
  until 
  the 
  middle 
  of 
  November 
  or 
  

   later, 
  being 
  apparently 
  dependent 
  to 
  some 
  extent 
  on 
  the 
  commencement 
  of 
  the 
  

   heavy 
  rains.* 
  As 
  a 
  striking 
  instance 
  of 
  the 
  effect 
  of 
  different 
  soil 
  conditions, 
  in 
  

   August 
  1916, 
  the 
  writer 
  crossed 
  the 
  Mafungabusi 
  plateau 
  towards 
  the 
  Umniati 
  River. 
  

   Water 
  is 
  well 
  held 
  on 
  the 
  plateau, 
  and 
  permanent 
  streams 
  pour 
  down 
  the 
  gorges 
  into 
  

   which 
  the 
  edge 
  is 
  broken, 
  only 
  to 
  lose 
  themselves 
  during 
  the 
  dry 
  season 
  in 
  the 
  deep 
  

   sand 
  which 
  extends 
  from 
  15 
  to 
  20 
  miles 
  between 
  the 
  plateau 
  and 
  the 
  Umniati 
  River. 
  

   On 
  the 
  plateau 
  the 
  whole 
  forest 
  was 
  in 
  full 
  leaf, 
  whilst 
  between 
  the 
  plateau 
  and 
  the 
  

   river 
  it 
  was 
  quite 
  leafless. 
  With 
  respect 
  to 
  mopani, 
  this 
  type 
  of 
  forest 
  has 
  never 
  

   been 
  noticed 
  in 
  foliage 
  between 
  the 
  end 
  of 
  July 
  and 
  the 
  beginning 
  of 
  November 
  and 
  

   has 
  frequently 
  been 
  noted 
  as 
  leafless 
  after 
  the 
  middle 
  of 
  the 
  latter 
  month. 
  

  

  During 
  the 
  leafless 
  period 
  tsetse 
  congregates 
  in 
  those 
  parts 
  of 
  the 
  fly 
  belt 
  where 
  

   there 
  are 
  evergreen 
  trees, 
  such 
  as 
  Ficus, 
  Acacia, 
  Parinarium 
  mobola, 
  Diospyros 
  

   mashuna, 
  Kigilia 
  pinnata, 
  etc. 
  Such 
  trees 
  occur 
  on 
  the 
  banks 
  of 
  water-courses 
  and 
  

   the 
  edges 
  of 
  vleis, 
  even 
  though 
  these 
  dry 
  up 
  on 
  the 
  surface 
  during 
  the 
  dry 
  season. 
  

   Some 
  of 
  them 
  are 
  also 
  found 
  on 
  " 
  ant-heaps 
  " 
  thinly 
  scattered 
  through 
  the 
  forest. 
  

   In 
  some 
  spots, 
  as 
  on 
  the 
  edges 
  of 
  vleis, 
  where 
  there 
  is 
  abundant 
  underground 
  water 
  

   the 
  Brachystegias 
  come 
  into 
  leaf 
  again 
  in 
  August, 
  even 
  though 
  the 
  vast 
  majority 
  of 
  

   the 
  same 
  species 
  in 
  the 
  vicinity 
  remain 
  leafless 
  till 
  the 
  advent 
  of 
  the 
  rains. 
  

  

  The 
  concentration 
  of 
  G. 
  morsitans 
  from 
  August 
  to 
  November 
  and 
  its 
  general 
  dis- 
  

   tribution 
  during 
  the 
  wet 
  season 
  and 
  first 
  half 
  of 
  the 
  winter 
  renders 
  observations 
  

   bearing 
  on 
  the 
  question 
  of 
  its 
  most 
  prolific 
  breeding 
  season 
  very 
  difficult 
  indeed. 
  

   There 
  is 
  a 
  general 
  opinion 
  that 
  the 
  fly 
  is 
  most 
  abundant 
  in 
  October 
  and 
  November, 
  

   and 
  this 
  may 
  be 
  the 
  case. 
  It 
  is 
  certainly 
  most 
  in 
  evidence 
  during 
  these 
  two 
  months, 
  

   but, 
  being 
  much 
  more 
  widely 
  scattered 
  at 
  most 
  other 
  times, 
  it 
  is 
  difficult 
  to 
  draw 
  

   comparisons. 
  Nevertheless, 
  the 
  establishment 
  of 
  the 
  fact 
  that 
  the 
  hot 
  months 
  pre- 
  

   ceding 
  the 
  rains 
  are 
  of 
  maximum 
  importance 
  to 
  the 
  welfare 
  of 
  the 
  fly 
  would 
  be 
  of 
  

   considerable 
  value. 
  It 
  may 
  well 
  be 
  that, 
  apart 
  from 
  the 
  breeding 
  rate, 
  the 
  summer 
  

   months 
  show 
  the 
  greatest 
  mortality 
  amongst 
  the 
  flies 
  from 
  the 
  attacks 
  of 
  insect 
  

   enemies 
  and 
  that 
  they 
  generally 
  become 
  reduced 
  in 
  numbers 
  during 
  this 
  period 
  ; 
  

   but 
  as 
  the 
  earliest 
  month 
  with 
  which 
  we 
  can 
  compare 
  the 
  prevalence 
  of 
  fly 
  at 
  any 
  

  

  *An 
  exception 
  occurred 
  during 
  the 
  present 
  year 
  (1918), 
  apparently 
  due 
  to 
  the 
  pheno- 
  

   menally 
  heavy 
  rains 
  of 
  last 
  season, 
  the 
  gusu 
  forest 
  being 
  generally 
  two 
  months 
  ahead 
  

   of 
  its 
  usual 
  time. 
  The 
  mopani, 
  however, 
  was 
  not 
  affected. 
  

  

  