Yea, I was wondering about Moth Balls too. Ha...The Moth Ball joke is an oldie but goodie!
I went out online to see what I could dig up...Seems as though Moth Balls, WD-40, Ivory bar
soap rubbed onto the surface, and dryer sheets are some of the things posted that seem to work. I'm thinking I'm going to try dryer sheets as they will be the easiest to secure. Definetly don't want them coming loose and clogging the air intake of the motors....Might also coat the inside of the dome with WD-40. It should leave an oil residue that might deter them from starting a nest.
Then there are fake wasp nests you can buy, like BeeeFree and Waspinator! They look like hornets nests...I don't think those would be a good idea for a car wash for obvious reasons....