822 
THE  TROPICAL  AGRICULTURIST. 
power  of  spinning  a thread  to  let  itself  down,  or  to 
come  home  again  by  in  passing  alarms,  during  the 
first  few  days  of  its  life.  After  that,  if  it  falls  to 
the  ground,  it  can  only  return  by  crawling. 
The  remedies  which  are  chiefly  used  all  turn  directly 
on  these  habits.  The  plan  of  driving  sheep  through 
an  infested  field,  or  of  brushing  the  plants  with 
boughs,  either  carried  by  hand  or  fixed  on  a scufilery 
or,  again  of  dragging  a cart-rope  over  the  plants, 
all  turn  on  endeavouring  to  make  the  caterpillars 
loose  their  hold,  which  we  see  amounts,  with  a large 
proportion,  to  the  same  thin"  as  killing  them  out- 
right._ 
As  in  the  case  of  turnip  flea  beetle,  various  kinds 
of  dressings  may  be  of  use,  such  as  lime,  &c.,  if 
applied  so  that  they  stick  to  the  insect  and  leafage  ; 
and  also  all  measures  to  keep  the  earth  moist 
enough  to  run  on  a good  crop,  and  keep  the  sawfly 
from  enjoyment  of  the  full  light,  heat,  and  drought, 
in  which  it  delights,  will  be  of  service. 
There  is  one  other  kind  to  bo  noticed,  because  it 
differs  greatly  from  those  just  named  in  its  habits. 
It  is  the  corn  sawfly  (Cephus  pi/iiniaius)  which  feeds 
more  es^iecially  within  the  wheat  stalks;  and  its 
presence  may  be  partially  known  by  the  blasted 
ear.  This  whitish  maggot  has  only  the  rudiments 
of  the  three  pairs  of  claw-feet ; and  when  its  work 
of  mischief  to  us  is  done,  it  rests  for  the  winter 
in  a silken  case,  very  near  ground  level,  in  the  sawn 
through  stalk.  To  prevent  attack  recurring,  it  is  a 
perfect  treatment  to  gather  together  the  infested 
stubble  and  burn  it.  This  is  an  exception  to  the 
usual  form  of  life  and  place  of  change  of  sawfly 
larvoe,  and  therefore  must  be  treated  differently ; 
but  there  is  the  same  principle  to  be  followed  as 
with  caterpillars  and  chrysalids  of  other  kinds  of 
sawflies,  and  also  of  butterflies  and  moths;  that  is, 
firstly,  to  find  out  where  they  pass  the  winter,  and 
then  to  turn  them  out  from  their  shelters. 
The  amount  of  injury  caused  by  sawfly  cater- 
pillars, and  especially  from  time  to  time  by  those 
of  the  turnip  sawfly,  is  so  serious  that  a great  deal 
has  been  written  (of  more  or  less  use)  on  the  sub- 
ject ; but  in  the  short  notes  of  the  five  kinds  of 
attack  mentioned  above,  it  will  be  seen  that  whether 
as  infestors  of  the  forest  tree  or  the  garden  fruit 
bush;  as  feeders  within  the  firm  fruit  of  the  apple, 
or  on  the  succulent  leaves  of  the  turnip,  or  carrying 
on  their  injurious  work  hidden  within  the  growing 
wheat-straw;  or,  again,  whether  the  larvae  or  cater- 
pillars are  possessed  of  22  or  20  feet,  or  (for  practical 
purposes)  of  no  feet  at  all,  there  is  one  method  of 
prevention  applicable  to  them  all — to  turn  out  the 
cocoons  and  destroy  them. 
The  families  of  the  parasite  wasp-flies  are  impor- 
tant to  us,  as  a means  of  keeping  the  increase  of 
other  insects  in  check.  One  division  of  these  is 
that  of  the  Ichneumon  flies.  These  are  much  like 
the  Ichneumon  parasite  of  the  corn  sawfly.  They 
are  lightly-made  insects,  with  a longish  body  and 
abdomen ; long  legs ; a small  head  with  long  horns, 
often  having  a ring  of  white  on  them  ; and  an  ovi- 
positor, sometimes  short,  sometimes  long,  and  often 
permanently  extended  like  a large  and  long  sting. 
With  this  they  insert  their  eggs,  for  the  most  part 
inio  the  grubs  of  other  insects,  but  sometimes  into 
their  eggs,  and  occasionally  into  the  chrysalids ; 
and  those  kinds  furnished  with  long  ovipositors 
pierce  with  them  through  bark  or  solid  wood,  and 
thus  insert  their  eggs  into  beetle  grubs,  or  what- 
ever their  selected  victim  may  be,  which,  although 
out  of  sight,  their  instinct  tells  them  is  within, 
ready  to  act  as  food  to  their  m iggots ; and  thus 
they  give  us  help  which  nothing  else  affords. 
In  the  case  of  corn-ears  which  are  infested  by 
aphides,  many  of  the  aphides,  instead  of  being  of 
the  natural  colour,  green  or  yellow,  brown  or 
other  tints,  will  be  seen  to  be  of  a rich,  brown,  or 
almost  black.  These  have  been  killed  by  the 
ichneumon.  The  leinale  of  the  AhhuhuH  inserts  a 
single  egg  ini-o  abdomen  of  many  aphides,  one 
after  the°  other,  and  the  nirggot,  which  hitches 
from  the  egg,  consumes  all  that  is  eatable,  until  its 
live  h st  is  reduced  to  a state  which  will  not  carry 
June  r,  1897. 
on  life  any  longer.  Its  uninvited  guest  goes  through 
its  changes  within  to  an  ichneumon  fly,  and  pie- 
sently  quits  the  harened  skin,  which  is  distinguished, 
as  just  observed  by  its  colour.  Sometimes  every 
aphis  on  a corn-ear  is  thus  destroyed,  and  the.e  are 
other  kinds  of  allied  parasite  flies  which  help  us 
similarl5\ 
One  of  the  forms  of  attack  which  is  the  plainest 
to  be  seen  is  that  of  the  cabbage  ichneumon  fly. 
This  little  fly  lays  a vast  number  of  eggs,  sometimes 
more  than  sixty,  in  one  caterpillar  of  the  large  cab- 
bage butterfly.  Here  the  maggots  hatch  and 
feed,  avoiding  by  instinct  such  parts  as  the  con- 
sumption of  would  cause  a fatal  loss,  to  the 
host,  and,  consequently,  to  the  guest.  The  con- 
taining caterpillar — the  live  food,  that  is — mean- 
while feeds  and  grows,  not  only  until 
it  attains  its  full  size,  but  it  may  often  be  known 
from  utiinfested  ones  by  its  swollen  appearance.  It 
has  not,  however,  power  to  turn  to  the  chrysalis 
state:  when  the  time  for  this  comes,  the  maggots 
within  pierce  its  skin,  and  each  one  spins  for  itself 
a small  cocoon  of  yellow  silk,  in  which  it  goes  through 
its  changes  to  the  complete  insect  by  the  side  of 
the  dead  body  of  the  exhausted  caterpillar.  These 
little  ichneumon  flies  are  one  of  our  protections 
against  great  increase  of  the  caterpillars,  and  the 
small  silken  cocoons,  which  are  easily  seen  when 
they  lie  together  in  masses  on  cabbage  leaves,  should 
never  be  destroyed. 
Another  kind  of  small  ichneumon  fly  [llemitehs 
melanarius),  preys  in  the  same  way,  by  means  of  its 
maggots,  inside  the  chrysalids  of  the  greenveined 
cabbage  butterfly.  These  infested  chrysalids  may  be 
known  by  their  dark  brown  colour,  and  should  never 
be  destroyed,  as  each  one  is  a case — package,  so  to 
say — full  of  checks  to  a troublesome  crop  preyer. 
All  these  ichneumon  flies  are  very  much  alike  in 
shape,  and  their  wings  are  much  veiued. 
The  parasite  wasp  flies  of  the  two  other  families, 
which  are  most  important  to  us  {Olialcididui  and 
Proctotrupida;),  are,  for  the  most  part,  very  small, 
with  almost,  or  quite,  veinless  wings.  The 
Pteromalua  puparum  is  one  of  the  kinds  which  des- 
troys chrysalids  of  the  large  and  small  cabbage 
butterflies.  This  very  small  fly  is  stated  to  lay  its 
eggs  on  the  outside  of  the  chrysalis,  as  soon  as  it 
has  cast  off  its  caterpillar  skin,  and  is  still  soft  and 
tender.  The  maggots  from  these  eggs  soon  hatch 
and  eat  into  the  chrysalis,  and  sometimes  as  many 
as  from  two  hundred  to  three  hundred  live  thus 
in  one  chrysalis,  where  they  change  to  the  perfect 
pirasite  fly,  and  come  out  soon  in  summer  to  con- 
tinue the  useful  work.  In  winter  some  remain  in 
the  chrysalis. 
The  use  of  these  Pleromali  is  well  shown  by  their 
work  in  North  America,  in  checking  increase  of 
cabbage  butterfly. 
The  small  white  cabbage  butterfly  made  its  ap- 
pearance (or,  at  least,  was  first  observed  there)  at 
Quebec  about  1859,  and  gradually  spread  and  caused 
much  damage,  but,  for  several  years  no  parasite 
appeared  to  check  it.  In  1871 — that  is,  about  twelve 
years  after  the  appearance  of  the  butterfly — it  was 
announced  that  the  parasite  we  are  now  speaking 
of  had  appeared : the  British  parasite  had  followed 
the  British  butterfly,  and  was  doing  its  appointed 
work.  In  1875  it  (the  p.irasite)  h id  become  quite 
common  in  the  State  of  New  York;  and  later  on 
it  was  observed  to  be  still  on  the  increase. 
The  great  benefit  gained  by  natural  helpers  of 
this  kind  has  caused  it  to  be  suggested  that  we  should 
rear  them.  This  matter  seems  rather  hard  to  manage; 
also  we  do  not  often  benefit  much  by  upsetting  the 
regular  balance  appointed;  but  it  is  often  in  our 
power  to  follow  up  a hint  of  this  kind,  by  remem- 
be.’ing  that  when  an  out-of-the-way  insect  enemy 
has  appeared,  wo  may  very  likely  be  able  also  to  in- 
troduce its  regular  check  and  leave  the  results  to  follow 
in  due  course.  Soincliines,  also  a now  infestation 
may  be  traced  home  to  the  country  from  which  it 
came  by  means  of  its  accompanying  parasites. 
In  the  memorable  appearance  of  the  Hessian  fly  in 
this  country,  wc  had  no  duo  to  lead  us  to  the 
