I spend a lot of time hiking around swampland, and know what you mean. Bug bites are aggravating. About the best you can do is applying "a lot"  directly to the skin AND then to your clothing. Be sure to saturate your skin at entry points where bugs can get into your clothing... such as below your pants legs, up your sleeves, down your shirt collar, etc. Use a repellant  that states it has 24 hour protection, although I doubt it really lasts that long. Sweating will lessin it's effect also, so I tend to reapply more than once on a trip.