When I try to use -B, I get an error. E.g.

$@ autossh -B wlan0 $HOST /usr/lib/autossh/autossh: invalid option -- 'B' usage: autossh [-V] [-M monitor_port[:echo_port]] [-f] [SSH_OPTIONS] ...

but if I swap autossh for ssh, it succeeds.

Why is autossh even trying to understand the -B?

I'm using autossh 1.4g on a debian-based distrubution.