It's either smell, body heat, or easy access to skin. Maybe you sweat more than your wife, or the compounds in your sweat are more attractive to mosquitos, or maybe her hygiene is better.

The smelliest parts of people are the sweat glands and mouth. I pay extra care to my smell when archery hunting by keeping my teeth brushed and using wet wipes on sweaty areas. Eating an apple also helps neutralize mouth odor.