I don't know if this helps you, but when I winter coleus I take cuttings. It's much easier to check over one section of stem and a few leaves. So far I haven't brought any hitch-hikers with me doing it this way.

Susan,
I too have had that problem...
The ones that are really hard to get rid of are the fungus gnats. They come from the soil and are like little fruit flies.
There are some yellow sticky strips you can buy that I have had some success with to trap them when they emerge. I also do not over water as that will bring more hatching..
If those are the ones you are seeing perhaps this will be of some help.
Good luck.
Lynn

Check out this link on Far North Forumn

Here is a link that might be useful: Bringing in plants for winter .. bug problems

Here's a suggestion: Put some isopropyl alcohol (70%) in a spray bottle, dilute it with some water, then spray (as in mist) the soil lightly if you see fungus gnats or thrips. Takes care of 'em instantly. I use this, with a few drops of dishwashing liquid as a surfactant, aphids, mealybugs, whitefly, spider mites (be sure to get the undersides of leaves). Works great. Gary

Put some isopropyl alcohol (70%) in a spray bottle, dilute it with some water,

(Gotta love it when people keep the actual proportions secret.)
------------------------
Don't forget that any topical spray will not kill eggs. You will always need to spray at least once more for the second generation of bugs in 3-5 days.

Here's a suggestion: Put some isopropyl alcohol (70%) in a spray bottle, dilute it with some water, then spray (as in mist) the soil lightly if you see fungus gnats or thrips. Takes care of 'em instantly. I use this, with a few drops of dishwashing liquid as a surfactant, aphids, mealybugs, whitefly, spider mites (be sure to get the undersides of leaves). Works great. Gary

Sorry about the double post; I left the computer and hit some button or other and that happened. Leftwood, you're right. I use 1:1 or 2:1 (water:alcohol), the stronger formula if whitefly, mealy bugs, or spider mites are the target.