By default, if you have the Pathauto module enabled and relevant patterns defined for your content, those patterns will be used during migration to automatically generate path aliases. To disable the application of Pathauto for a migration:

1. Install and enable the Migrate Extras module.
2. Add a field mapping explicitly setting the 'pathauto' field to 0 in each content migration:
   

   $this->addFieldMapping('pathauto')
        ->defaultValue(0);