Bugs & worms in the stems of my plants?

I've moved my plants outside this growing season because I ran out of room inside. Now, I'm running into bugs that bore a hole into the stem of the plant. They are eating their way through the stem which is causing the plants to wilt. I'm sure because the stem can no longer carry the water and nutrients past the point of entry. When I put the plants in the ground, I put "collars" around them. Some are even still in the buckets just sitting outside. Do I cut the plant just below the point of entry, simply spray with insecticide, or what? Please help before it's too late.