85 
When  the  boats  are  at  a  good  distance 
from  the  shore,  mosquitos  are  not  seen  in  day¬ 
time.  At  twilight  and  at  night,  some  species, 
chiefly  of  Mansonia  and  Cellia,  are  attracted  by 
the  lights  and  may  appear  on  board,  but  they 
are  not  nearly  so  numerous  as  when  the  boat 
is  near  to,  or  moored  at  the  bank. 
Several  kinds  of  Simulium  apparently  like 
following  rivers  where  the  air  is  al¬ 
ways  damp.  Sometimes  they  are  found  up  to 
thirty  miles  from  their  breeding  places  ;  I  had 
already  noticed  this  on  the  São  Francisco 
river,  and  observed  it  again  on  the  Paraná.  Si¬ 
mulium  amazonicam  is  found  on  all  the  large 
rivers,  where  there  are  falls,  and  is  most  an¬ 
noying  when  one  travels  by  water.  Onshore, 
horses  are  more  persecuted  than  their 
riders. 
In  the  ports  some  flies  belonging  to  the 
Anthracidae  and  Muscidae  groups  came  on 
board,  while  others  bred  there  or  were  ship¬ 
ped  with  goods. 
At  night,  many  more  insects  appear,  speci¬ 
ally  when  the  boats  are  well  lit.  On  dark  nights 
they  are  more  numerous  but  generally 
small  in  size.  The  moths  are  mostly  small 
and  Microlepidoptera  prevail.  The  díptera 
are  chiefly  small  Nematocera  with  aquatic 
larvae,  specially  Chironomidae.  When  the 
river  winds  through  marshy  regions,  their 
number  increases  considerably.  Trichoptera  and 
Neuroptera  with  aquatic  larvae  are  also  found 
in  many  individuals,  but  in  few  species.  Most 
of  them  are  Plecoptera  of  the  genus  Périodes ; 
Ephemeridae  appear  ocasionally,  while  some 
species  of  Trichoptera  are  more  regularly  ob¬ 
served.  Í  noticed  a  Leptonema  and  another  one, 
which  probably  belongs  to  a  new  genus  of 
Macrontinatinae  ( Hy dropsy chidae ).  A  goodly 
number  of  brazilian  Trichoptera  is  alreadly 
known  but  there  must  be  many  more.  Their 
preservation  is  difficult,  as  the  body  is  very 
soft  while  the  antennae  are  fragile  and 
often  extremely  long. 
Unlike  the  clear  streams  coming  from  the 
mountains,  the  turbid  waters  of  large  rivers, 
depositing  quantities  of  mud,  are  unfavoura¬ 
ble  media  for  aquatic  larvae  and  only  a  small 
number  of  species  have  adapted  themselves 
to  them,  though  there  may  be  many  individu¬ 
als.  They  are  of  practical  interest  as  food  for 
fishes  but  their  study  must  be  left  for  the  future. 
Where  many  insects  appear,  spiders  are 
always  found  and  this  is  true  even  on  board 
ship. 
2.  Blood-sucking  Díptera. 
Acording  to  all  accounts,  the  summer  of 
1917-18  was  unfavourable  for  the  collecting 
of  insects  in  the  regions  of  the  Paraná  and 
of  Paraguay  through  which  we  passed.  This 
was  due  to  a  spell  of  dry  weather  just  be¬ 
fore  the  summer  and  to  a  great  frost  in 
winter,  which  was  still  indicated  by  the  large 
number  of  dry  branches  hanging  on  the 
trees.  To  add  to  this,  the  best  season  was 
already  over  and  we  were  only  able  to  col¬ 
lect  on  river  banks  or  on  board  ship.  In 
spite  of  these  difficulties,  we  collected  and 
preserved  about  600  insects,  besides  many 
which  were  not  mounted.  We  did  not  find 
many  new  species  but  made  some  interes¬ 
ting  observations  on  the  distribution  of  he- 
matophagous  díptera.  Partly  for  this  reason 
and  partly  on  acount  of  its  practical  interest, 
I  shall  deal  with  this  group  first,  beginning 
with  the  Culicidae. 
Culicidae. 
Anophelinae.  Of  this  sub-family,  we  only 
found  two  kinds  of  Cellia.  One  was  C.  ar- 
gyrotarsis  which  must  be  considered  the 
transmissor  of  malaria  among  the  inhabitan- 
ts  of  the  Upper  Paraná  and  the  crews  of  boats 
who  spend  the  night  in  foci  of  infection.  Some 
specimens  were  caught  in  Porto  Tibiriçá  and 
many  others  were  captured  on  board  the 
launch,  on  an  excursion  to  the  Ivahy  river. 
Of  C.  albimana,  only  a  few  specimens  ap¬ 
peared  on  the  Upper  Paraná.  At  the  time 
the  rivei  was  high  and  the  conditions  unfa¬ 
vourable  to  the  breeding  of  these  mosquitos; 
as  it  happens  on  other  rivers,  many  more 
might  have  been  found  at  a  different  period. 
In  any  case  the  intervention  of  other  mos¬ 
quitoes  is  not  necessary  to  explain  the  pre¬ 
sence  of  malaria  in  this  region. 
