Generally, beta sites can't have migration paths (I remember there was an exception, but I forgot which beta site has it).
From What is the reasoning behind restricting the number of migration paths?, Shog9 explained the problem with migration, especially on beta sites. In summary,
Think about this: it takes 5 people to vote to migrate a question. At which point, the destination site gets to decide whether or not the question is appropriate, potentially rejecting it. [...]
The question still wasn't written by someone familiar with the site where it ends up posted. They had no opportunity read the Help Center or About pages, or even to see existing questions on the site! The question probably isn't well-tagged (indeed, the system will automatically reject questions that have no valid tags on the destination), and very possibly missing details that are important to the folks who would be most likely to answer it...
[U]sers don't get migrated. They get notified of the migration, but they still have to go set up an account on the destination site before they'll be notified of any comments or answers left on their question post-migration. So requests for clarification often go unheard. This is never fun for anyone, but it's particularly harsh on a small and growing community still trying to establish their scope and standards for quality - for this reason, we do not create default migration paths to beta sites, and strongly discourage even moderators from migrating to/from sites in their formative stages.
[I]n most cases, it's more effective - and certainly more expedient - to skip migration entirely and just vote to close as off-topic while leaving a comment directing the asker to a more appropriate site (or sites...). This gives the asker a chance to create an account and familiarize himself with the community and their scope before throwing his question up, and also tends to weed out some of the folks less willing to put any real effort into addressing criticism.