"Is icing sugar the same as powdered sugar?"
Confectioner sugar is not the same as powdered sugar. I made my own powder sugar from
the regular C&H sugar and other brands of sugar in a small commercial powder grinding machine. This is also the process I use to make plenty of sugar bricks by grinding the sugar to a fine powder first.
The icing sugar has corn flour mixed with powder sugar which is not the same as pure powdered sugar. Either way if any hit the developing larvae they will be kill. That is why I don't use the sugar dusting method at all after learning about this side effect.
Also, in between the foragers and young nurse bees, there is another level of bees, the comb guard bees. They are just a bit mature than the young nurse bees in the hive. Their job is to safeguard the comb, young nurse bees and developing larvae. They are not the typical guard bees that fly to sting you when you approach the hive. They are a bit immature than the guard bees or foragers. They do not fly or feed the developing larvae. The next step is for them to turn into some of the foragers or guard bees.
So by leaving the frame of bees out of the hive for an extended time, these comb guard bees will not leave the frame that they're trying to protect. And since they are a bit older than the young nurse bees, they will not hesitate to be aggressive toward any foreign new queen that they have contact with. So if there is an old queen inside the present hive and you add this frame of new bees in, they might ball on the old queen.
Listen for the queen's intense piping sound when she is caught by the balling bees. If the balling is extensive then most likely one of her hind legs will be disabled--not salvageable. What a waste of a good laying queen!
Be careful when adding new foreign bees into a suspected queen less hive. To be safe, I would get rid of all the attaching bees from the frame first before adding it to the queen less hive. What a sad way for me to learn after killing too many good queens that I raised.