This appears to be one of the solitary wasps or bees, and I suspect it was testing the stem to see if it was hollow. These types of wasps often use hollow-stemmed plants to build their nests. I can't tell from the image, exactly which wasp/bee it is. Some of wasps provision the burrows with paralyzed insects that are used to feed their larvae, and the bees use pollen and nectar to feed their larvae.  I wouldn't worry about it as we generally don't want to kill either type of beneficial insects, even when they cause minor damage on our plants.