An idea came to me as I was eating Sweet and Spicy Chili Doritos (Yes, the same ones endorsed by Col. Hoffman).
What about a vehicle that acted as a submarine, only it didn't submerge under water, but had a large drill bit on the front and was able to flow through dirt and rock with ease?
Beat the Locust at their own game of making "emerging holes" and make "submerging holes" and invade the Locust instead of them invading the humans on the surface.
Or, perhaps a missle that would burrow underneath the surface of the planet on its own and drill down several miles beneath the surface and plant itself and detonate itself and really affect the Locust en mass.
Just some thoughts.