﻿696 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  by 
  General 
  Francis 
  A. 
  Walker, 
  from 
  the 
  StatiHtics 
  of 
  Agriculture, 
  Ninth 
  

   Census, 
  1870. 
  

  

  This 
  insect 
  is 
  double-brooded, 
  as 
  the 
  flies 
  appear 
  both 
  in 
  spring 
  and 
  

   autumn. 
  At 
  each 
  of 
  these 
  periods 
  the 
  fly 
  lays 
  twenty 
  or 
  thirty 
  eggs 
  in 
  a 
  

   crease 
  in 
  the 
  leaf 
  of 
  the 
  young 
  plant. 
  In 
  aboutfour 
  days, 
  in 
  warm 
  weather, 
  

   they 
  hatch, 
  and 
  the 
  pale-red 
  larviB 
  (Fig. 
  2a) 
  " 
  crawl 
  down 
  the 
  leaf, 
  work- 
  

   ing 
  their 
  way 
  in 
  between 
  it 
  and 
  the 
  main 
  stalk, 
  passing 
  downward 
  till 
  

   they 
  come 
  to 
  a 
  joint, 
  just 
  above 
  which 
  they 
  remain, 
  a 
  little 
  below 
  the 
  

   surface 
  of 
  the 
  ground, 
  with 
  the 
  head 
  toward 
  the 
  root 
  of 
  the 
  plant." 
  

   (Plate 
  lY, 
  Fig. 
  Ic.) 
  Here 
  they 
  imbibe 
  the 
  sap 
  by 
  suction 
  alone, 
  and 
  

   by 
  the 
  simple 
  pressure 
  of 
  their 
  bodies, 
  they 
  become 
  imbedded 
  in 
  the 
  

   side 
  of 
  the 
  stem. 
  Two 
  or 
  three 
  larvfe 
  thus 
  imbedded 
  serve 
  to 
  weaken 
  

   the 
  plant 
  and 
  cause 
  it 
  to 
  wither 
  and 
  die. 
  The 
  larvse 
  become 
  full-grown 
  

   in 
  five 
  or 
  six 
  weeks, 
  then 
  measuring 
  about 
  three-twentieths 
  of 
  an 
  inch 
  

   in 
  length. 
  About 
  the 
  1st 
  of 
  December 
  their 
  skin 
  hardens, 
  becoming 
  

   brown, 
  and 
  then 
  turns 
  to 
  a 
  bright 
  chestnut 
  color. 
  This 
  is 
  the 
  so-called 
  

   flaxseed 
  state, 
  or 
  puparium. 
  In 
  two 
  or 
  three 
  weeks 
  the 
  "larva" 
  (or, 
  

   more 
  truly 
  speaking, 
  the 
  semi-pupa) 
  becomes 
  detached 
  from 
  the 
  old 
  

   case. 
  In 
  this 
  puparium 
  some 
  of 
  the 
  larva 
  remains 
  through 
  the 
  winter. 
  

   Toward 
  the 
  end 
  of 
  April 
  or 
  the 
  beginning 
  of 
  May 
  the 
  pupa 
  (Plate 
  LXV, 
  

   Fig. 
  1&) 
  becomes 
  fully 
  formed, 
  and 
  in 
  the 
  middle 
  of 
  May, 
  in 
  ]^ew 
  Eng- 
  

   land, 
  the 
  pupa 
  comes 
  forth 
  from 
  the 
  brown 
  puparium, 
  " 
  wrapped 
  in 
  a 
  

   thin 
  white 
  skin," 
  according 
  to 
  Herrick, 
  "which 
  it 
  soon 
  breaks 
  and 
  is 
  

   then 
  at 
  liberty." 
  The 
  flies 
  appear 
  just 
  as 
  the 
  wheat 
  is 
  coming 
  up 
  ; 
  they 
  

   lay 
  their 
  eggs 
  for 
  a 
  period 
  of 
  three 
  weeks, 
  and 
  then 
  entirely 
  disappear. 
  

   The 
  maggots 
  hatched 
  from 
  these 
  eggs 
  take 
  the 
  flaxseed 
  form 
  in 
  June 
  

   and 
  July, 
  and 
  are 
  thus 
  found 
  in 
  the 
  harvest 
  time, 
  most 
  of 
  them 
  remain- 
  

   ing 
  on 
  the 
  stubble. 
  Most 
  of 
  the 
  flies 
  appear 
  in 
  the 
  autumn, 
  but 
  others 
  

   remain 
  in 
  the 
  puparium 
  until 
  the 
  following 
  spring. 
  By 
  burning 
  the 
  

   stubble 
  in 
  the 
  fall 
  their 
  attacks 
  may 
  best 
  be 
  prevented. 
  Among 
  the 
  

  

  parasites 
  on 
  this 
  species 
  are 
  the 
  egg-parasites, 
  

   Platygaster 
  and 
  Semiotellus 
  {Ceraphron) 
  des- 
  

   tructor 
  Say 
  (Fig. 
  3), 
  the 
  latter 
  of 
  which 
  pierces 
  

   the 
  larva 
  through 
  the 
  sheath 
  of 
  the 
  leaf. 
  Two 
  

   other 
  Ichneumon 
  parasites, 
  according 
  to 
  Her- 
  

   rick, 
  destroy 
  the 
  fly 
  while 
  in 
  the 
  flaxseed 
  or 
  

   semi-pupa 
  s'tate. 
  The 
  ravages 
  of 
  the 
  Hessian 
  

   fly 
  have 
  been 
  greatly 
  checked 
  by 
  these 
  minute 
  

   insects, 
  so 
  that 
  it 
  is 
  in 
  many 
  localities 
  not 
  so 
  

   destructive 
  as 
  it 
  was 
  formerly. 
  Dr. 
  Fitch 
  has 
  

   suggested 
  that 
  the 
  European 
  parasites 
  of 
  this 
  

   insect, 
  and 
  the 
  wheat-midge, 
  could 
  be 
  imported 
  

   Fig. 
  3.— 
  Parasite 
  of 
  the 
  and 
  bred 
  in 
  large 
  quantities, 
  so 
  as 
  to 
  stop 
  their 
  

   Hessian 
  Fly. 
  ravages. 
  With 
  proper 
  pecuniary 
  aid 
  from 
  the 
  

  

  State 
  this 
  seems 
  feasible, 
  while 
  our 
  native 
  parasites 
  might 
  perhaps 
  also 
  

   be 
  bred 
  and 
  multiplied 
  so 
  as 
  to 
  eftectually 
  exterminate 
  these 
  pests. 
  As 
  

   regards 
  the 
  increase 
  of 
  parasites, 
  B. 
  Wagner, 
  in 
  his 
  " 
  Researches 
  on 
  the 
  

   new 
  Corn 
  [wheat] 
  Gall-fly" 
  (Marburg, 
  1861), 
  finds 
  that 
  the 
  parasites 
  of 
  

   the 
  Hessian 
  fly 
  increase 
  in 
  a 
  ratio 
  corresponding 
  to 
  that 
  of 
  their 
  hosts. 
  

   In 
  the 
  same 
  year, 
  he 
  says, 
  in 
  which 
  the 
  hosts 
  are 
  very 
  generally 
  frequent, 
  

   they 
  are 
  so 
  infested 
  by 
  parasites 
  that 
  the 
  next 
  year 
  only 
  a 
  few 
  of 
  the 
  

   gali-flies 
  appear. 
  He 
  also 
  found 
  that 
  the 
  parasites 
  only 
  infested 
  the 
  

   summer 
  brood 
  of 
  Hessian 
  flies, 
  but 
  not 
  the 
  winter 
  brood 
  ; 
  seventy 
  per 
  

   cent, 
  of 
  the 
  former 
  were 
  found 
  to 
  be 
  infested. 
  Thus 
  far 
  the 
  Hessian 
  fly 
  

   has 
  not 
  occurred 
  west 
  of 
  the 
  Mississippi 
  Valley. 
  

  

  Egg 
  and 
  larva 
  : 
  The 
  egg 
  is 
  about 
  oue-fiftieth 
  of 
  an 
  inch 
  long 
  and 
  fonr-thousandtli3 
  

   of 
  an 
  inch 
  in 
  diameter, 
  cylindrical, 
  translucent, 
  and 
  of 
  a 
  pale-red 
  color 
  (Herrick). 
  

  

  