Not that I know of. Have you actually tried just going into into phpMyAdmin and looking around? I have several users set up for several databases, and have never been asked to select a user to use phpMyAdmin. That doesn't mean it's not automatically selecting a/the user when I select a particular database. Come to think of it, if you have Drupal running, you must already have a user defined anyway.
The first thing to try is robots.txt to control where in your site spiders can go. Tell all bots to stay out of places where they have no business going (such as login and profile pages). Some bots may also obey various settings for how long to stay on-site and how often to visit. If some spiders don't obey robots.txt, then once you identify them by IP address, you can deny (ban) them by IP addresses in .htaccess.