About 30 years ago I read a guidebook to outdoor activities which claimed that taking large doses of Vitamin B1 for a number of days (weeks?) would make you less appealing to the bugs. I don’t know whether there is any scientific evidence for that. Some people definitely do attract more bugs. Wearing any kind of floral perfume or fragrance is bad (for humans), and certain colors of clothing are supposed to be bad. I noticed that this nonanal stuff is supposed to smell fruity or flowery. The main diet of mosquitoes, esp. males (who do not bite) is nectar.
I have read that north wood Indian guides stop eating sugar about 6 weeks before bug season. Could be they become less sweet and attractive. I have cut my sugar eating back a lot and also take Vitamin C 3 or 4 times a day, and mosquito bites rarely ever bother me although I still get them from time to time. Used to suffer terribly at the beach, New Jersey and Virginia.