use strict;
use warnings;

$/ = "//";

my $genfile = "c:\bemisia_coi.gb";
open my $ifh, "<", $genfile or die "cannot open $genfile: $!\n";

while (my $chunk = <$ifh>){
  last if eof $ifh;
  my ($accession) = $chunk =~ /LOCUS\s*([A-Z]*\d+)/;
  my ($biotype) = $chunk =~ /BIOTYPE\s*([A-Z])/;
  my ($sequence) = $chunk =~ /ORIGIN\s*(.*)$/s;
  $sequence =~ s/\s|\d//g;
  my $outfile = "${accession}_${biotype}";
  open my $ofh, '>' $outfile or die "cannot open $outfile: $!\n";
  print $ofh, ">$accession\n$sequence";
  close $ofh;
}