A very simple trap using…
1. An empty plastic bottle
2. A small piece of banana skin (had to fish one off the compost heap)
3. A cone of paper (reused a drawing kindly supplied by Edie)
Put the banana skin inside the bottle, make a paper cone with a small whole to fit inside the bottle neck and fasten on using tape so flies can’t get out around the edge of the paper. Within a few hours the kitchen was clear of flies and they were all having a jolly old time feasting on the banana skin but couldn’t figure out how to get out.
How to get rid of fruit flies using a basic trap « Becoming Domestic
You could try that until you nuke 'em.