﻿SCALE 
  INSECTS 
  OF 
  IMPORTANCE 
  293 
  

  

  Injuries. 
  The 
  harm 
  done 
  by 
  scale 
  insects 
  is 
  seldom 
  appreciated 
  till 
  

   it 
  is 
  too 
  late. 
  The 
  scales 
  may 
  be 
  noticed 
  on 
  the 
  bark 
  in 
  considerable 
  

   numbers, 
  but 
  so 
  long 
  as 
  the 
  tree 
  shows 
  no 
  marked 
  injury, 
  the 
  majority 
  

   of 
  people 
  are 
  inclined 
  to 
  believe 
  that 
  but 
  little 
  harm 
  has 
  been 
  done. 
  They 
  

   appear 
  to 
  overlook 
  the 
  fact 
  that 
  a 
  tree, 
  like 
  a 
  man, 
  may 
  put 
  forth 
  every 
  

   possible 
  effort 
  to 
  sustain 
  itself 
  and 
  apparently 
  succeed 
  in 
  doing 
  so, 
  only 
  

   to 
  collapse 
  suddenly 
  at 
  the 
  end. 
  Every 
  living 
  scale 
  insect, 
  after 
  it 
  has 
  

   become 
  established, 
  is 
  an 
  automatic 
  pump 
  drawing 
  the 
  vital 
  fluids 
  from 
  

   the 
  host 
  plant 
  through 
  a 
  slender, 
  hair-like 
  beak 
  or 
  proboscis 
  (pi. 
  3, 
  fig. 
  10). 
  

   The 
  amount 
  insects 
  are 
  capable 
  of 
  abstracting 
  in 
  this 
  way 
  from 
  a 
  tree 
  is 
  

   truly 
  surprising. 
  I 
  have 
  repeatedly 
  seen 
  showers 
  of 
  honeydew 
  falling 
  

   from 
  elms 
  badly 
  infested 
  with 
  the 
  elm 
  bark 
  louse, 
  the 
  excretion 
  being 
  so 
  

   copious 
  as 
  to 
  keep 
  the 
  walk 
  beneath 
  wet 
  even 
  on 
  good 
  drying 
  days. 
  

   This 
  abundant 
  excretion 
  is' 
  not 
  seen 
  in 
  the 
  case 
  of 
  the 
  armored 
  scales, 
  

   like 
  the 
  species 
  to 
  be 
  considered 
  later, 
  but 
  the 
  production 
  of 
  their 
  firm, 
  

   protective 
  coverings, 
  as 
  well 
  as 
  the 
  nutrition 
  of 
  the 
  thousands 
  of 
  insects, 
  

   must 
  make 
  an 
  enormous 
  draft 
  on 
  the 
  infested 
  tree. 
  This 
  is 
  proved 
  by 
  

   the 
  fact 
  that 
  not 
  infrequently 
  trees 
  are 
  unable 
  to 
  withstand 
  the 
  drain 
  and 
  

   succumb. 
  The 
  injury 
  these 
  species 
  can 
  inflict 
  is 
  in 
  a 
  measure 
  directly 
  

   proportional 
  to 
  their 
  productivity. 
  A 
  moderately 
  prolific 
  species 
  pos- 
  

   sessing 
  the 
  ability 
  to 
  develop 
  several 
  generations 
  in 
  a 
  season 
  is 
  one 
  to 
  be 
  

   feared, 
  because 
  under 
  favoring 
  conditions 
  a 
  much 
  larger 
  number 
  of 
  in- 
  

   dividuals 
  might 
  be 
  produced 
  than 
  would 
  be 
  possible 
  for 
  a 
  much 
  more 
  

   prolific 
  species 
  which 
  was 
  limited 
  by 
  nature 
  to 
  one 
  generation 
  annually. 
  

   It 
  is 
  the 
  same 
  for 
  one 
  year 
  as 
  the 
  relation 
  existing 
  between 
  arithmetical 
  

   and 
  geometric 
  progression. 
  This 
  is 
  why 
  the 
  San 
  Jose 
  scale 
  is 
  so 
  danger- 
  

   ous. 
  It 
  is 
  not 
  only 
  moderately 
  prolific, 
  but 
  it 
  develops 
  a 
  number 
  of 
  gen- 
  

   erations 
  in 
  a 
  season. 
  It 
  has 
  been 
  estimated 
  that 
  in 
  one 
  year 
  in 
  the 
  lati- 
  

   tude 
  of 
  Washington 
  (D. 
  C.) 
  a 
  single 
  female 
  might 
  produce, 
  all 
  condi- 
  

   tions 
  such 
  as 
  food 
  supply, 
  etc. 
  being 
  favorable, 
  the 
  enormous 
  number 
  of 
  

   3,216,080,400 
  descendants. 
  

  

  Means 
  of 
  dispersal. 
  This 
  is 
  an 
  extremely 
  important 
  matter, 
  par- 
  

   ticularly 
  to 
  the 
  man 
  -whose 
  trees 
  are 
  free 
  from 
  these 
  pests. 
  The 
  period 
  

   when 
  any 
  of 
  the 
  scale 
  insects 
  to 
  be 
  considered 
  below 
  can 
  travel 
  of 
  their 
  

   own 
  free 
  will 
  is 
  very 
  limited 
  and, 
  excluding 
  the 
  males, 
  which 
  may 
  be 
  dis- 
  

   regarded 
  in 
  this 
  connection, 
  they 
  are 
  wingless 
  and 
  their 
  crawling 
  powers 
  

   by 
  no 
  means 
  great. 
  These 
  scale 
  insects 
  depend 
  almost 
  entirely 
  on 
  some 
  

   external 
  agency 
  to 
  transport 
  them 
  even 
  from 
  tree 
  to 
  tree, 
  unless 
  the 
  limbs 
  

   interlock. 
  It 
  has 
  been 
  demonstrated 
  by 
  Prof. 
  W. 
  G. 
  Johnson 
  that 
  the 
  

  

  