Friend uses vinegar & eucalyptus essential oil mix as a spray on his horse to keep flies away effectively. Simple. Essential oils are amazingly easy & don't impact your nervous system (yep) diluted tea tree (kills ants on the spot/roaches hate it), lemongrass (citronella) quite the mosquito deterrent. 'Fruit flies' are often just that - an indicator of nearby fruit/garage, dog poop, etc. Flies don't like ammonia either.. Save pesticides for the scorpions.