User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-26074976-20140603192318/@comment-184612-20140603235313

You just feed the Hunting Bug for whichever stats you want. They're upgradeable when the feeding meter is full, and usually must be upgraded before you can upgrade the Insect Glaive itself. Certain evolutions require stats to be at a certain level (personally I prefer the Speed types).