User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-26074976-20140507085750/@comment-184612-20140507132810

The hunting bug is unique to each Glaive, it upgrades as you upgrade it. If you end up with a bug you don't like, you'd have to remake the weapon. Each Insect Glaive has a certain Type of Hunting Bug that it will get, either Slash or Impact (which I have listed in the weapon tables). Each Type of bug has its own evolution path which is governed by the 3 stats, Power, Speed, and Stamina.

The way upgrading the Insect Glaive works is you feed the bug until it is full, and then you are able to level it up. You'll see on the weapon tree that there's a level range on each weapon. That's the level range for the bug before you can upgrade the Insect Glaive itself. So, if an Insect Staff is listed as Slash LV1-3 then it'll be a Slash Type bug that you'll have to level up to level 3 before you can upgrade the Glaive itself to its next form. As for the Hunting Bug evolutions, I believe they happen at level 3 and 6 (it's been awhile) where it will have to reach certain prerequisite stats in order to upgrade down either the Power, Speed (my personal favorite), Stamina, or Balanced paths.