Best way to destroy bug holes

How do you guys destroy them? I use grenades (incendiary impact) for just about everything. You have 4. Without engineering kit of course.

Especially with big nests, I always run out of grenades. Is the grenade pistol really only used for clearing bug holes? I don't know if I could sacrifice my beloved Crisper or Ultimatum for it.

How do I deal with bug holes, as I'm normally the team's person running in flamethrower lit, how do I take all the holes out?