﻿REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  231 
  

  

  and 
  of 
  the 
  Agricultural 
  Dei)artment 
  at 
  Washington, 
  and 
  from 
  different 
  

   newspapers, 
  as 
  well 
  as 
  from 
  private 
  correspondence. 
  The 
  record, 
  as 
  

   therein 
  presented, 
  is 
  very 
  imperfect, 
  but 
  still 
  is 
  sufficient 
  to 
  show 
  the 
  

   periodicity 
  in 
  the 
  return 
  of 
  periods 
  when 
  the 
  Hessian 
  Fly 
  has 
  been 
  suffi- 
  

   ciently 
  abundant 
  to 
  ravage 
  wheat-tields 
  and 
  excite 
  apprehension 
  and 
  

   alarm. 
  Without 
  much 
  doubt, 
  in 
  the 
  different 
  States 
  mentioned, 
  espe- 
  

   cially 
  in 
  the 
  Middle 
  States, 
  the 
  insect 
  is 
  tolerably 
  abundant 
  nearly 
  every 
  

   year, 
  but 
  few 
  seasons 
  occurring 
  when 
  after 
  a 
  careful 
  search 
  by 
  experts 
  

   the 
  fly 
  would 
  not 
  be 
  found. 
  

  

  As 
  the 
  recorded 
  facts 
  indicate, 
  within 
  about 
  ninety 
  years 
  there 
  have 
  

   been, 
  in 
  the 
  Atlantic 
  and 
  Middle 
  States, 
  six 
  periods 
  of 
  unusual 
  abun- 
  

   dance, 
  namely, 
  centering 
  about 
  the 
  years 
  1790, 
  1817, 
  1844-'45, 
  1871-'72, 
  

   and 
  1876-78. 
  These 
  dates, 
  which 
  generally 
  are 
  Inserted 
  in 
  larger 
  type 
  

   in 
  the 
  table, 
  mark 
  the 
  time 
  of 
  culmination 
  in 
  the 
  degree 
  of 
  abundance 
  

   and 
  extent 
  of 
  ravages 
  committed, 
  and 
  were 
  preceded 
  by 
  from 
  one 
  to 
  

   several 
  years 
  of 
  less 
  or 
  greater 
  abundance. 
  After 
  the 
  culmination, 
  or 
  

   year 
  of 
  greatest 
  abundance, 
  the 
  fly 
  often 
  suddenly 
  disappears. 
  This 
  

   sudden 
  disai)pearance 
  is, 
  without 
  doubt, 
  due 
  to 
  the 
  great 
  increase 
  in 
  the 
  

   number 
  of 
  parasites, 
  while 
  the 
  original 
  increase 
  is 
  probably 
  due 
  to 
  a 
  suc- 
  

   cession 
  of 
  warm, 
  damp 
  seasons, 
  favorable 
  to 
  the 
  multiplication 
  of 
  the 
  

   flies. 
  These 
  seasons, 
  when 
  we 
  look 
  at 
  the 
  later 
  Hessian 
  Fly 
  years, 
  such 
  

   as 
  1844-^45, 
  1871-'72, 
  and 
  1876-'78, 
  when 
  the 
  insect 
  had 
  become 
  wide- 
  

   spread 
  over 
  the 
  western 
  portion 
  of 
  the 
  wheat 
  area, 
  were 
  evidently 
  areas 
  of 
  

   similar 
  climatic 
  features 
  common 
  to 
  the 
  Atlantic 
  and 
  Mississippi 
  Valley 
  

   States. 
  Whether 
  these 
  seasons 
  were 
  warm 
  and 
  moist 
  or 
  not, 
  we 
  have 
  

   not 
  the 
  means 
  at 
  hand 
  to 
  enable 
  us 
  to 
  form 
  an 
  opinion. 
  

  

  As 
  stated 
  to 
  us 
  by 
  Mr. 
  Thomas, 
  in 
  1817 
  the 
  rainfall 
  from 
  Maine 
  to 
  

   Maryland 
  was 
  slightly 
  above 
  the 
  average, 
  1.01 
  per 
  cent, 
  of 
  the 
  mean. 
  

  

  The 
  winter 
  of 
  1843-'44 
  was 
  the 
  most 
  severe 
  in 
  the 
  West 
  that 
  had 
  been 
  

   experienced 
  for 
  twenty 
  years 
  j 
  the 
  spring 
  was 
  cold 
  and 
  late 
  ; 
  1844 
  was 
  

   very 
  wet 
  over 
  the 
  West, 
  in 
  fact 
  the 
  wettest 
  season 
  known 
  since 
  its 
  set- 
  

   tlement, 
  or 
  at 
  least 
  since 
  1811. 
  This 
  was 
  the 
  year 
  of 
  the 
  great 
  flood 
  in 
  

   the 
  Mississippi. 
  It 
  was 
  also 
  wet 
  in 
  parts 
  of 
  Virginia 
  and 
  Maryland. 
  

   But 
  along 
  the 
  sea-coast, 
  from 
  Maine 
  to 
  Florida, 
  the 
  amount 
  of 
  rainfall 
  

   was 
  only 
  about 
  .90 
  per 
  cent, 
  of 
  the 
  mean. 
  In 
  1845 
  it 
  was 
  not 
  very 
  wet 
  

   in 
  any 
  section 
  where 
  wheat 
  was 
  cultivated, 
  the 
  amount 
  along 
  the 
  sea- 
  

   coast 
  being 
  placed 
  at 
  .95, 
  and 
  this 
  was 
  about 
  the 
  same 
  in 
  the 
  Middle 
  

   and 
  Northwestern 
  States, 
  varying 
  from 
  .83 
  to 
  .91 
  per 
  cent, 
  of 
  the 
  mean. 
  

  

  We 
  thus 
  see 
  that 
  the 
  Hessian 
  Fly 
  years, 
  1817 
  and 
  1844, 
  were 
  wet 
  

   years, 
  periods 
  of 
  more 
  than 
  the 
  average 
  rainfall. 
  Of 
  1871 
  we 
  have 
  no 
  

   records 
  at 
  hand 
  ; 
  the 
  spring 
  and 
  summer 
  of 
  1877 
  were 
  damp 
  and 
  wet, 
  

   and 
  also 
  appear 
  to 
  have 
  been 
  warmer 
  than 
  the 
  previous 
  year. 
  There 
  

   thus 
  appears 
  to 
  be 
  a 
  correlation 
  between 
  the 
  seasons 
  of 
  greatest 
  abun- 
  

   dance 
  of 
  Hessian 
  Flies 
  and 
  a 
  greater 
  degree 
  of 
  moisture, 
  if 
  not 
  of 
  heat. 
  

  

  