I had the same problem a few months ago. I used some of those yellow sticky traps (no chemicals involved) and placed them near a lamp outside of my grow area. they were attracted to the light and the yellow of the traps and within a week or so all of them were out of my grow and within a week of that all of them dead or gone. though i went through like 4 of the traps but they were cheap, like less than 5$ for a pack of them from walmart. I also put sand over the top layer of my soil then removed the sand when they were gone. good luck.