It really depends on what you plan to be doing and where you'll be and how wet it's been. I hike quite a bit and generally end up with lots of bites. I'll sometimes get a few in town in the evening. In Hana, especially, you should expect mosquitoes. As alternatives to DEET, you can wear clothes treated with permethrin or use the non-smelly picaridin repellent.
Efficacy: Picaridin was tested against mosquitoes, flies and ticks in both field studies and in laboratory cage tests. Against certain strains of mosquitoes, Picaridin provides equal or longer protection than identical concentrations of DEET. Efficacy against ticks has been demonstrated in laboratory cage tests.
Cosmetics: Picaridin has been successfully tested with dermatologist. It will not cause irritations on your skin and is nearly odorless.
http://www.picaridin.com/science.htm