I've used a pesticide sprayer and gasoline to take out bag-worms for years.
Gives you a cone of flame about three wide aat a distance of five feet from the tip. Or you can loosen the tip and get a stream about fifteen feet long.
But if you want real dramatic stuff, try diesel fuel in one of those syringe-type giant squirters. Have a bucket of water handy to suck back into the gun and put out any flame that gets inside, though.