No cause for alarm yet! You can take my word on that. I am currently in Australia where SHB was introduced in 2000 unofficially. Unfortunately I had to be the one to discover the darn thing.
I work at a University and am currently studying SHB with a world Authority on SHB, and his group from Germany. They have studied beetle populations in every country they exist.
In our area at present, all hives contain in excess of 60 beetles, more commonly 100plus.
Hives can sustain this number until high humidity and colony disturbance occur. Then you get a total meltdown.
In fact yesterday we found a hive that holds the world record of beetles collected 2200. This is uncommon and is what is known as an aggregation site (pheromones at work). All I can say is lucky we found them and sucked them up with our vacuum sampler.
With the numbers you have just keep squashing them for now and removing larva. Make sure you have good ventilation and airflow. Placing a stick under the lid helps dramatically. Don't feed patties while adult beetles are present. This just provides a medium for larval reproduction.
Hives need to be kept strong. Remove any comb that is being neglected otherwise the larva will work from the outside combs and eventually consume the hive. This can happen within 3 days.
An extra hint. If a hive looks like it might break down (greasy sweaty look) remove 1 frame from the all boxes and increase bee space for 24 hrs before returning frames to the hive. This allows the bees to clean the hive and harass beetles which often leave.