I dislike the idea of insect repellant myself. If you shouldn't eat it, you shouldn't put it on your skin. Try doing the exercises indoors, while imagining you are outdoors. (It'll be quite effective, especially since you have to use your mind to 'create' or sense the Qi of sun, clouds, sky, earth, etc--and you will in that sense be connecting with them) Then take a 30 min walk, while doing Qi Gong breathing. This will give you extra balance in your exercises and you'll still get the qi exchange with the outside. Since you are moving while walking, insects shouldn't have time to be able to land on you.
Just a thought.
~Z