In far off New Zealand I lived for 8 years in an area where we had things called sandflies - horrible little pests a bit like blackfly I think. Nothing much seemed to stop them but for mosquitos which were also a problem I used to take extra large doses of Vitamin B especially B2. Mosquitos really did not like it at all and stayed away. My Husband said I smelled a bit strange but he could cope!
Might be worth a try.