﻿GENERAL 
  REPORT 
  FOR 
  1881. 
  37 
  

  

  along. 
  During 
  flight 
  their 
  position 
  is 
  generally 
  face 
  to 
  the 
  wind 
  and 
  

   partially 
  elevated. 
  At 
  l^ast 
  this 
  is 
  the 
  position 
  in 
  which 
  I 
  have, 
  noticed 
  

   great 
  numbers 
  of 
  them 
  while 
  drifting. 
  They 
  do 
  not 
  fly, 
  but 
  float 
  on 
  

   the 
  breeze, 
  and 
  move 
  no 
  faster 
  than 
  the 
  wind 
  does. 
  

  

  While 
  on 
  the 
  move 
  their 
  actions 
  are 
  controlled 
  to 
  a 
  great 
  extent 
  by 
  

   the 
  atmospheric 
  conditions 
  which 
  have 
  already 
  been 
  noticed 
  under 
  the 
  

   head 
  of 
  "general 
  notes." 
  When 
  hungry 
  they 
  come 
  down 
  and 
  feed, 
  and 
  

   then 
  are 
  oft* 
  again. 
  This 
  state 
  of 
  aflairs 
  continues 
  until 
  near 
  the 
  time 
  

   for 
  commencing 
  operations 
  for 
  the 
  continuation 
  of 
  their 
  kind. 
  This 
  

   takes 
  place 
  within 
  two 
  or 
  three 
  weeks 
  after 
  obtaining 
  wings. 
  Coition 
  

   and 
  egg 
  depositing 
  are 
  then 
  kept 
  ux> 
  alternately 
  until 
  cold 
  weather 
  sets 
  

   in 
  or 
  until 
  they 
  die 
  of 
  exhaustion 
  j 
  the 
  number 
  of 
  egg 
  deposits 
  made 
  

   by 
  a 
  single 
  female 
  varying 
  from 
  one 
  to 
  four, 
  each 
  of 
  which 
  averages 
  25 
  

   eggs; 
  the 
  interval 
  between 
  egg 
  deposits 
  being 
  from 
  four 
  to 
  eight 
  or 
  

   more 
  days 
  according 
  to 
  the 
  state 
  of 
  the 
  weather 
  and 
  the 
  vigor 
  of 
  the 
  

   insect, 
  it 
  being 
  much 
  more 
  frequent 
  in 
  favorable 
  weather 
  and 
  with 
  

   healthy 
  and 
  vigorous 
  females. 
  After 
  egg 
  laying 
  is 
  over 
  they 
  die 
  from 
  

   the 
  effects 
  of 
  frosts 
  and 
  from 
  the 
  exhaustion 
  brought 
  on 
  by 
  the 
  exer- 
  

   tions 
  of 
  reproduction. 
  

  

  "How 
  does 
  it 
  happen 
  that 
  this 
  insect 
  becomes 
  so 
  exceedingly 
  numer- 
  

   ous 
  at 
  times 
  when 
  other 
  species 
  remain 
  normal?" 
  is 
  a 
  question 
  that 
  has 
  

   frequently 
  been 
  submitted 
  to 
  me. 
  My 
  answer 
  is, 
  through 
  its 
  migratory 
  

   habits 
  and 
  the 
  character 
  of 
  its 
  native 
  habitat. 
  As 
  soon 
  as 
  surroundings 
  

   become 
  adverse 
  to 
  its 
  increase, 
  it 
  has 
  but 
  to 
  launch 
  itself 
  into 
  the 
  air 
  

   and 
  be 
  off 
  for 
  a 
  locality 
  where 
  these 
  are 
  favorable, 
  and 
  where 
  there 
  are 
  

   few 
  or 
  no 
  enemies 
  ; 
  while 
  species 
  not 
  possessing 
  this 
  habit 
  are 
  obliged 
  

   to 
  remain 
  and 
  struggle 
  on 
  in 
  the 
  best 
  way 
  they 
  can. 
  While 
  migration 
  

   <loes 
  not 
  always 
  prove 
  beneficial 
  in 
  this 
  direction, 
  the 
  cases 
  where 
  it 
  

   does 
  not 
  are 
  so 
  very 
  few 
  that 
  in 
  the 
  end 
  they 
  are 
  not 
  noticeable. 
  

  

  If 
  we 
  take 
  any 
  insect 
  that 
  has 
  gradually 
  developed 
  this 
  habit 
  we 
  find 
  

   one 
  that 
  has 
  become 
  alarmingly 
  common 
  and 
  destructive. 
  The 
  Colorado 
  

   Potato 
  Beetle, 
  for 
  instance, 
  is 
  an 
  example 
  of 
  this 
  sort. 
  But 
  a 
  very 
  

   few 
  years 
  ago 
  we 
  only 
  heard 
  of 
  it 
  as 
  being 
  found 
  in 
  moderate 
  numbers 
  

   feeding 
  on 
  a 
  wild 
  species 
  of 
  solanum 
  {Solanum 
  rostrattim) 
  —a 
  native 
  of 
  

   (^^olorado 
  and 
  adjacent 
  country. 
  On 
  the 
  approach 
  of 
  man, 
  however, 
  

   with 
  his 
  cultivated 
  i)lants 
  it 
  found 
  a 
  new 
  solanaceous 
  plant 
  that 
  it 
  i)re- 
  

   ferred 
  to 
  its 
  old 
  and 
  long-used 
  one. 
  The 
  growth 
  of 
  the 
  latter 
  being 
  

   certain 
  and 
  not 
  fortuitous 
  gave 
  this 
  insect 
  a 
  basis, 
  and 
  in 
  a 
  very 
  few 
  

   years 
  it 
  began 
  to' 
  move 
  from 
  field 
  to 
  field, 
  establishing 
  colonies 
  wherever 
  

   it 
  went, 
  until 
  now 
  it 
  lias 
  not 
  only 
  spread 
  throughout 
  all 
  Eastern 
  North 
  

   America, 
  but 
  has 
  also 
  succeeded 
  in 
  reaching 
  Europe. 
  Although 
  not 
  a 
  

   parallel 
  case 
  with 
  that 
  of 
  C. 
  spretus^ 
  it 
  is 
  a 
  fair 
  example 
  of 
  how 
  migra- 
  

   tion 
  favors 
  the 
  increase 
  of 
  a 
  particular 
  species 
  of 
  insect 
  in 
  contradis- 
  

   tinction 
  to 
  one 
  that 
  is 
  non 
  migratory. 
  The 
  Chinch 
  Bug 
  and 
  Cotton 
  

   Worm 
  are 
  also 
  examples 
  of 
  the 
  increase 
  by 
  migration 
  or 
  moving 
  from 
  

   one 
  locality 
  to 
  another. 
  

  

  