I think the $dbh->do() method wants an "attributes" (think of options) hashref as the second argument (which is being passed through to prepare() ). I.e. you'd need to specify an empty hashref if you don't have any options to pass:

my $numrows = $dbh->do($insert_query, {}, $date,$fields[3],...);
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Update:  it appears that undef would work, too (in place of {}) — see the example in the docs.