How to kill fruit flies without apple cider vinegar?
Answers:
White vinegar with a splash of dishwashing detergent in it. I find that the white vinegar works much better than apple cider vinegar.
Other answers:
Get rid of whatever is attracting them.
Get rid of whatever is attracting them.
This isn't really the answer you're looking for, but fruit flies hate mint. You can buy mint extract or mint oil and they will not come around it.
First, get rid of any softened, rotting fruit, or anything sweet that is found on the counter tops (opened soda cans, beer bottles, alcohol, fruit juice, sugars, etc) and take out the trash immediately. Second, clean the countertops with an all purpose cleaner of your choice (Clorox Cleanup, Lysol All Purpose Lemon spray, Fantastic, etc). Once all foods for the fruit flies are gone they will disappear. Also, if you have a garbage disposal pour white vinegar down the drain while running it for a few seconds. Fruit flies also like garbage, recycling bins, and dirty mop water (anywhere something can be rotting) Wash out the trash can and recycling bins because the garbage bags leak sometimes. The site below offers some good information on fruit flies.
In my experience, this works without the need for "traps". With nothing to feed on the can't live.
Fruit juice and liquid soap. Beer and liquid soap.