﻿61 
  

   TWO 
  PESTS 
  OF 
  MAHOGANY 
  IN 
  NYASALAND. 
  

   By 
  E. 
  Ballard. 
  

  

  Government 
  Entomologist, 
  Nyasaland 
  Protectorate. 
  

  

  Mahogany 
  trees 
  are 
  attacked 
  by 
  two 
  caterpillars 
  which 
  inflict 
  a 
  large 
  amount 
  of 
  

   damage 
  every 
  year. 
  One 
  of 
  these, 
  Heteronygmia 
  leucogyna, 
  Hmp. 
  (Lymantriidae), 
  

   eats 
  the 
  leaves, 
  while 
  the 
  other, 
  Mussidia 
  albipartalis, 
  Hmp. 
  (Pyralidae), 
  bores 
  

   under 
  the 
  bark, 
  causing 
  much 
  deformity 
  of 
  young 
  trees 
  and 
  the 
  formation 
  of 
  corky 
  

   excrescences, 
  accompanied 
  by 
  the 
  exudation 
  of 
  resin. 
  

  

  The 
  main 
  points 
  of 
  the 
  life-history 
  of 
  Heteronygmia 
  leucogyna 
  are 
  as 
  follows. 
  

   Between 
  150 
  and 
  200 
  eggs 
  are 
  laid 
  in 
  a 
  single 
  batch, 
  generally 
  low 
  down 
  on 
  the 
  trunk 
  

   of 
  the 
  tree. 
  These 
  eggs 
  are, 
  when 
  first 
  laid, 
  of 
  a 
  milky-white 
  colour, 
  smooth 
  and 
  

   spherical, 
  with 
  slightly 
  flattened 
  upper 
  pole. 
  Just 
  before 
  they 
  hatch 
  they 
  become 
  

   dark 
  owing 
  to 
  the 
  presence 
  of 
  the 
  contained 
  embryo. 
  After 
  about 
  nine 
  days, 
  the 
  

   young 
  larvae 
  emerge, 
  through 
  the 
  top 
  of 
  egg. 
  When 
  just 
  hatched 
  they 
  measure 
  

   3 
  mm. 
  in 
  length, 
  and 
  are 
  pale 
  yellow 
  in 
  colour, 
  with 
  bunches 
  of 
  fine 
  hairs. 
  The 
  full 
  

   grown 
  larvae 
  vary 
  slightly 
  in 
  colour, 
  some 
  being 
  very 
  pale, 
  while 
  others 
  are 
  darker, 
  

   with 
  dark 
  heads. 
  All 
  the 
  larvae 
  have 
  a 
  very 
  flattened 
  appearance, 
  and 
  are 
  marked 
  

   dorsally 
  with 
  black 
  and 
  red. 
  The 
  length 
  of 
  the 
  full-grown 
  larvae 
  is 
  3 
  cm. 
  The 
  pupa 
  

   is 
  formed 
  in 
  a 
  very 
  slight 
  cocoon 
  consisting 
  of 
  a 
  few 
  threads, 
  generally 
  on 
  the 
  under 
  

   side 
  of 
  a 
  leaf, 
  or 
  on 
  an 
  excrescence 
  on 
  the 
  bark. 
  The 
  colour 
  of 
  the 
  pupa 
  varies 
  from 
  

   green 
  to 
  brown. 
  The 
  pupation 
  period 
  lasts 
  for 
  ten 
  days. 
  

  

  Both 
  the 
  larvae 
  and 
  eggs 
  of 
  H. 
  leucogyna 
  are 
  heavily 
  parasitised. 
  Two 
  species 
  of 
  

   Chalcididae, 
  and 
  one 
  Ichneumon, 
  Ecthromorpha 
  variegata, 
  Brull6, 
  have 
  been 
  bred 
  

   from 
  the 
  larvae. 
  During 
  May 
  and 
  June 
  nearly 
  90 
  per 
  cent, 
  of 
  eggs 
  collected 
  were 
  

   found 
  to 
  be 
  parasitised, 
  but 
  those 
  collected 
  during 
  September 
  and- 
  October 
  were 
  

   unaffected. 
  

  

  The 
  larvae 
  of 
  H. 
  leucogyna 
  are 
  extremely 
  voracious, 
  and 
  last 
  rainy 
  season 
  practi- 
  

   cally 
  defoliated 
  the 
  mahogany 
  plantation 
  in 
  the 
  Bwaila 
  Gardens, 
  near 
  Zomba. 
  They 
  

   were 
  also 
  extremely 
  destructive 
  to 
  the 
  trees 
  shading 
  one 
  of 
  the 
  roads 
  in 
  Zomba 
  town- 
  

   ship. 
  

  

  The 
  bark-borer 
  of 
  mahogany 
  is 
  the 
  larva 
  of 
  Mussidia 
  albipartalis, 
  Hmp. 
  It 
  is 
  

   most 
  destructive 
  and 
  disfiguring 
  to 
  mahogany 
  trees. 
  Young 
  trees 
  which 
  are 
  attacked 
  

   by 
  this 
  insect 
  are 
  contorted 
  and 
  twisted, 
  and 
  the 
  growth 
  of 
  the 
  main 
  stem 
  is 
  frequently 
  

   arrested. 
  Large 
  excrescences 
  are 
  formed 
  at 
  the 
  point 
  of 
  attack, 
  and 
  in 
  some 
  cases 
  

   the 
  entire 
  trunk 
  of 
  the 
  tree 
  is 
  gnarled 
  and 
  roughened, 
  and 
  drips 
  with 
  resin 
  as 
  the 
  

   result 
  of 
  the 
  activities 
  of 
  these 
  insects. 
  On 
  well-grown 
  trees 
  their 
  depredations 
  are 
  

   confined 
  to 
  the 
  cambium, 
  but 
  in 
  young 
  trees 
  and 
  small 
  twigs 
  they 
  often 
  bore 
  right 
  

   down 
  the 
  middle 
  after 
  the 
  manner 
  of 
  a 
  Cerambycid 
  or 
  other 
  wood-boring 
  larva. 
  When 
  

   climbing 
  plants, 
  such 
  as 
  the 
  chitedze 
  bean 
  are 
  twined 
  round 
  the 
  stem 
  of 
  a 
  tree 
  infested 
  

   with 
  Mussidia 
  the 
  larvae 
  work 
  spirally 
  round 
  the 
  tree 
  under 
  the 
  stem 
  of 
  the 
  climber, 
  

   and 
  they 
  generally 
  appear 
  to 
  show 
  a 
  predilection 
  for 
  working 
  where 
  there 
  is 
  some- 
  

   thing 
  pressing 
  against 
  the 
  tree 
  trunk, 
  or 
  where 
  branches 
  fork. 
  

  

  The 
  life-history 
  has 
  been 
  only 
  partially 
  elucidated. 
  The 
  eggs 
  are 
  apparently 
  laid 
  

   on 
  the 
  trunk. 
  The 
  young 
  larva 
  on 
  hatching 
  begins 
  to 
  bore 
  into 
  the 
  bark 
  at 
  once. 
  

   The 
  full 
  grown 
  larva 
  is 
  about 
  one 
  inch 
  in 
  length, 
  and 
  is 
  coloured 
  blue-grey, 
  or 
  grey- 
  

  

  