288 
Whatever  has  been  attained  up  to  now  with  the  natural  method 
is  due  to  experiments  undertaken  and  carried  through  in  some 
cases  with  good  results,  especially  in  the  United  States  (main- 
land) and  the  Hawaiian  Islands.  I therefore  believe  that  it  would 
be  useful  to  add  to  this  treatise  an  account  of  what  has  been  ac- 
complished in  these  countries;  also  what  little  has  been  practiced 
elsewhere  following  their  example.  Thus  one  will  get  an  idea  of 
what  has  been  done  in  this  field  and  will  also  be  able  to  under- 
stand how  much  may  and  must  still  be  tried  with  prospects  of 
good  results. 
Facts  which  make  the  natural  method  advisable.  It  has  always 
been  very  obvious  for  anybody,  seeing  one  insect  devour  another, 
that  injurious  insects  must  also,  at  least  in  part,  be  devoured  by 
other  insects,  properly  called  predators. 
Acute  observers,  naturalists  and  specially  entomologists  who 
make  a study  of  insect  life,  had  since  remote  times  had  occasion 
to  notice  that  often  from  the  egg  or  from  the  chrysalis  of  a given 
insect  not  an  individual  of  the  same  species  is  born,  but  one  or 
more  individuals  belonging  even  to  different  orders,  so  that  from 
the  larva  of  a given  species  instead  of  passing  through  the 
consecutive  stages  peculiar  to  it,  at  a certain  moment  of  its  de- 
velopment, larvae  of  other  insects  appear  because  the  former  has 
been  killed  by  these  larvae  of  other  insects,  who  devour  it  from 
the  inside  or  suck  it  dry  from  the  outside.  These  are  the  parasitic 
insects,  which  have  been  noticed  since  remote  times,  and  of  which 
the  internal  ones  have  been  called  “entophagi”  by  Rondani  and 
the  external  ones  “ectophagi”  by  myself. 
Aldrovandi  (1602)  was  the  first  to  observe  the  exit  of  the 
larvae  of  Apanteles  glomeratus  (which  he  held  to  be  eggs)  from 
the  common  cabbage  caterpillar  and  later  Redi  (1668)  published 
the  same  observation  and  another  on  insects  of  different  species 
born  of  the  same  pupa. 
But  to  Valisnieri  belongs  the  merit  to  have  discovered  first 
the  real  nature  of  parasitic  insects  on  others  and  to  have  written 
about  the  form  and  biology  of  many  which  he  had  discovered. 
About  the  nature  and  work  of  these  parasites  he  wrote,  “if 
sometimes  there  are  born,  (from  one  insect  different  ones)  they 
are  what  I should  call,  false  individuals,  being  born  from  a differ- 
ent kind  of  worms  which  have  been  deposited  there  by  their 
mothers,  so  that  they  may  feed  off  the  real  native  worm.  This 
is  a law,  ordained  in  this  base  world  by  the  Supreme  Creator 
which  I have  not  yet  well  understood,  that  the  larger  always  de- 
vours the  smaller,  and  is  its  tyrant,  a law  which  I have  constantly 
observed  in  all  forms  of  life,  winged,  fourfooted  and  aquatic.” 
Cestoni,  a contemporary  of  Valisnieri,  in  a letter  to  him  speaks 
at  length  about  the  parasites  of  Aphis  brassicae,  Pieris  brassicae, 
and  finally  of  Aleyrodes  brassicae.  He  calls  the  insects  of  this 
latter  species  first  “ butterfly  atoms’  and  then  <(little  cabbage 
sheep ” and  their  parasites,  “wolf -mosquito.” 
