First of all the lost princes actions dedication is to be commended. Have the messengers relay the news to the populous before returning to him. The tale might take some of this sting out of losing the berry bush.

And about that berry bush. We needs to [i]impress[/i] upon these beetles that actions like this won't be tolerated. Once our numbers are back up muster our forces to the the border, make it look like we're massing for an attack. But send a team of workers tunneling under the ground. These fortifications we had aren't built to our new standards, and we already know they are prone to collapse. Undermine them, bring them down, and in the resulting confusion have our forces sweep in and wipe out all beetles intruding on our territory. There are less of them than us and it would take a significant number to occupy our old defences, so this would be a terrible blow. 

We can not suffer our own works being turned on us. It is offensive!