Is it really necessary to apply a repellent for clothing?
YES
The blood meal is vital to the existence of biting insects, either for nourishment (as in ticks) or for the maturation of eggs (as in mosquitoes). Therefore, they will do anything to bite, and will seek out the slightest gap in your defences.
40% of mosquito bites take place through clothing, so it is strongly recommended to wear clothing that has been pre-sprayed with pyrethroid-based repellent as a complement to bodily protection of exposed skin.