The best researched oil to fight mosquitoes is the Australian lemon eucalyptus.
http://www.picaridin.info/lemon-eucalyptus.htm
Keep in mind that all essential oils best are dilluted before skin contact its unwise to use them pure.
To make a sprayer that can create an aërosol you can dillute in some pure alcohol and then add water or (as i prefer) a hydrosol.
Aromatharapy does not replace doctors advice!
Be sure to keep them out of reach for children and never use undilluted oil on skin or in bathing.
The internal use of essential oils shoud not be done without guidance of a certified aromatherapist - there are health risk to it.