﻿DIRECTION 
  AND 
  VELOCITY 
  OF 
  WIND. 
  31 
  

  

  not 
  live 
  upon 
  this 
  tree. 
  This 
  being 
  the 
  case, 
  dispersion 
  by 
  the 
  wind, 
  

   which 
  is 
  concerned 
  chiefly 
  with 
  small 
  caterpillars, 
  is 
  limited 
  in 
  its 
  

   results 
  by 
  the 
  food 
  plants 
  which 
  the 
  young 
  caterpillars 
  are 
  able 
  to 
  

   reach, 
  and 
  this 
  depends 
  somewhat 
  upon 
  the 
  ability 
  of 
  the 
  larva? 
  to 
  

   crawl. 
  For 
  instance, 
  if 
  caterpillars 
  are 
  blown 
  by 
  the 
  wind 
  and 
  drop 
  

   on 
  cultivated 
  ground 
  or 
  in 
  pastures, 
  they 
  must 
  perish 
  on 
  account 
  of 
  

   scarcity 
  of 
  food. 
  Similarly, 
  if 
  caterpillars 
  lodge 
  in 
  solid 
  pine 
  

   forests 
  (PI. 
  XIII) 
  they 
  will 
  perish 
  for 
  want 
  of 
  suitable 
  food. 
  

   In 
  fact, 
  the 
  establishment 
  of 
  the 
  pest 
  in 
  this 
  way 
  depends 
  upon 
  the 
  

   larva? 
  being 
  able 
  to 
  find 
  suitable 
  food. 
  Either 
  the 
  larva? 
  must 
  be 
  

   dropped 
  by 
  the 
  wind 
  on 
  a 
  food 
  plant 
  that 
  is 
  favorable 
  for 
  their 
  de- 
  

   velopment 
  or 
  they 
  must 
  fall 
  within 
  crawling 
  distance 
  of 
  it. 
  In 
  many 
  

   sections 
  of 
  the 
  country 
  the 
  foliage 
  is 
  unfavorable 
  for 
  gipsy-moth 
  food; 
  

   hence 
  colonies 
  have 
  not 
  become 
  established. 
  

  

  CONDITION 
  OF 
  FOOD 
  PLANTS. 
  

  

  The 
  condition 
  of 
  the 
  trees 
  in 
  an 
  infested 
  area 
  has 
  an 
  important 
  

   relation 
  to 
  the 
  liability 
  of 
  the 
  spread 
  of 
  the 
  insect. 
  Unfavorable 
  

   food, 
  coupled 
  with 
  warm 
  weather, 
  naturally 
  stimulates 
  the 
  activity 
  

   of 
  the 
  larvae, 
  and 
  this 
  increases 
  the 
  chances 
  for 
  spread. 
  If 
  there 
  are 
  

   dead 
  trees 
  in 
  the 
  infested 
  area 
  the 
  chances 
  of 
  wind 
  spread 
  of 
  the 
  

   larva? 
  from 
  them 
  are 
  greater 
  than 
  on 
  healthy 
  trees, 
  as 
  the 
  caterpillars 
  

   are 
  unprotected 
  from 
  the 
  sun 
  and 
  wind 
  and 
  move 
  about 
  continually 
  

   in 
  search 
  of 
  food 
  if 
  the 
  temperature 
  is 
  high 
  enough. 
  

  

  DIRECTION 
  AND 
  VELOCITY 
  OF 
  THE 
  WIND. 
  

  

  Of 
  all 
  of 
  the 
  factors 
  thus 
  far 
  enumerated 
  perhaps 
  no 
  one 
  is 
  as 
  

   important 
  with 
  regard 
  to 
  dispersion 
  as 
  is 
  the 
  wind. 
  The 
  others 
  

   may 
  be 
  regulated 
  or 
  controlled 
  to 
  some 
  extent 
  but 
  it 
  is 
  impossible 
  to 
  

   do 
  this 
  with 
  the 
  wind. 
  For 
  instance, 
  it 
  is 
  possible 
  to 
  reduce 
  the 
  in- 
  

   festation 
  in 
  any 
  area 
  so 
  that 
  wind 
  spread 
  is 
  nearly 
  precluded, 
  because 
  

   it 
  is 
  dependent 
  upon 
  the 
  factors 
  which 
  have 
  been 
  mentioned, 
  which, 
  

   with 
  the 
  exception 
  of 
  temperature, 
  can 
  be 
  controlled. 
  

  

  The 
  natural 
  trend 
  of 
  dispersion 
  of 
  the 
  gipsy 
  moth 
  has 
  been 
  toward 
  

   the 
  north 
  and 
  northeast. 
  The 
  spread 
  of 
  the 
  brown-tail 
  moth 
  has 
  

   been 
  chiefly 
  in 
  a 
  northeasterly 
  direction, 
  and 
  the 
  reason 
  attributed 
  

   to 
  this 
  has 
  been 
  that 
  the 
  prevailing 
  wind 
  during 
  July, 
  when 
  the 
  

   moths 
  are 
  flying, 
  was 
  from 
  the 
  opposite 
  direction. 
  Since 
  (he 
  aviation 
  

   of 
  first-stage 
  gipsy-moth 
  larva' 
  lias 
  been 
  proved, 
  it 
  is 
  evident 
  that 
  

  

  a 
  part, 
  at 
  Least, 
  of 
  the 
  more 
  newly 
  infested 
  area 
  is 
  due 
  to 
  the 
  action 
  of 
  

   the 
  wind. 
  It 
  is 
  also 
  true 
  that 
  the 
  prevailing 
  winds 
  in 
  April 
  and 
  May. 
  

  

  wIhm) 
  (lie 
  Larvae 
  are 
  small 
  enough 
  to 
  be 
  distributed 
  in 
  this 
  way. 
  is 
  

   chiefly 
  from 
  the 
  south 
  and 
  southwest. 
  'Fable 
  II 
  gives 
  the 
  record 
  of 
  

  

  wind 
  direction 
  for 
  20 
  days 
  in 
  April 
  and 
  May, 
  when 
  the 
  temperature 
  

  

  