Depends on the characteristics of the trap, the bait and the bug, doesn't it? A highly attractive trap with a steep drop-off, and large and effective kill zone, and a kind of bug with a small but active nightly migration radius (when near campers) (compared to the trap attraction radius) might quickly attract and kill all the bugs that will come into that radius that night.

When you kill all those bugs in the first hour of the night, does that leave a noticeable excess-food signal in the region where the dead bugs use to be?