In reply to Flinticus:
Citronella candles are probably the least effective insect repellent, the odour of citronella is volatile and moves away fast and I don't know if there's any evidence that it repels insects anyway.
Those repellers linked are just another variation on the heated mat containing pyrethrum, which does work. Hotels in Africa have them but by the time the mozzie is in your room the only remedy is insecticide spray.
We have found that mosquito coils, which are also pyrethrum, burned around the tent entrance work well. Burn them inside the tent and midges die in 15 minutes but everything will smell smokey and you will get mild bronchitis from the smoke.