There’s even the old Marx brothers joke “time flies like an arrow; fruit flies like a banana”

The fruit fly trap taught to me by an entomologist friend is baited with wine, suggesting the fruit flies want fermenting fruit

The trap: get a plastic fizzy drink bottle; bigger is better

Cut off the top. The cut piece is a cone

Place the cone (the top piece) upside down on the rest of the bottle

Sticky tape the joint

Bait with cheap wine or leftover wine or beer

Her tastes were revealed in the description of baiting the trap — she specified red wine, but I have tested with various booze and fruit flies have no taste, they’ll go for anything. You could probably extract bait from the sourdough starter you made in lockdown and kept alive despite never making bread after that first try