I haven't tried this but my acupuncturist told me that pennyroyal herb can work as a pesticide. I am not sure if you grind up the herb and sprinkle it around, or make tea and spray it around - perhaps the internet can help with those questions - but she advocated its use to get rid of fleas. I have thankfully not had trouble with fleas for many years (that is why I can't remember the details of what she told me!) but if I had them again I would certainly try something natural before getting into the chemical sprays, if possible.
A word of warning, though - Pennyroyal can be a very effective abortifacient - so do NOT use it if you are pregnant or trying to get pregnant, or having visitors who are!