Cockroach or insects triggering conductive ink sensor
I doubt you'll have much luck with resistive sensing - the chitin shell and legs of an insect will have a very high resistance. Any voltage high enough to give reasonable current is likely to cook the little buggers. Not that that's a bad thing, of course.

By the same token, I'm dubious about the capacitance, as well.

I'd suggest a different approach, such as optical sensing.