Wasps can sometimes be a problem, depending on the year and the location. Wasps are mainly looking for water on hot days, but they also like the sweetness of the grapes. Attracted by the scent, wasps come flying around, and go for the berries. Once the skin is cracked and the 'buffet' open, neighboring bees also like to drop in for a drink. They may sting when disturbed while feasting.
Mesh nets help against wasps-- gauze or fly screens, especially. The nets can cover whole grape areas or be wrapped around individual grape clusters. The classic wasp trap of hanging a narror-necked bottles with juice won't solve the problem-- this tends to lure more wasps than it catches!