Cats do not like citronella, or lemon scents. I have bought three lemon scent thyme and that seems to work.
Citronella candles will stop all insects from biting you when you sit in the garden. So yes they will keep the insects away. Also when ants come into the house a bit of sliced lemon will deter them.
My favourite and best working cat deterrent is a very cheap curry powder, just a little sprinkle and you won't see those cats. Mrs Bouquet