OK. so, I've been doing some experiments on my own regarding the grapefruit.
Grapefruit JUICE (fresh squeezed) is most effective. You don't need a lot. It does not dry sticky UNLESS you glob it on, which you don't have to do. I tried using grapefruit rind and although it works, it doesn't work as well as the juice. Rub a rind on your arm and It does not dry sticky at all.
I cut a grapefruit in half and put it on the table outside. I sat outside and was pleasantly surprised that no bugs bit me the whole time I was out there (1 hour). Smelled nice too.
I've been experimenting with it when I go out and work on my bee hive. I'll report in when I get more data. (will they ignore me or bite me?)
Enjoy!