How can I prevent "bees" from damaging my grape crop?

The bee-like insects are probably yellowjackets.  Yellowjackets are social wasps that build paper nests either in the ground, a log or landscape timber, or building wall or attic.  The workers from the colony travel up to a few hundred yards from the nest while looking for food.  In early summer, the wasps forage for caterpillars and other “meat” items and are beneficial predators.  However, in late summer they prefer sweets such as soda pop, candy and the sweet juices of fruits and vegetables. 

Discourage yellowjackets from feeding on the grapes by harvesting the grape clusters as soon as they ripen.  Remove any over-ripe or damaged fruit from the garden area.  Do not leave beverages, candy or other food items in the vicinity of the grapevines as they may attract yellowjackets to the area. 

Traps can be used outside the perimeter of the planting to discourage yellowjackets from feeding on the grapes.  Place the traps before the berries begin to ripen.  Different baits and traps may have to be tried to determine if any traps/baits will work in the grape planting.  Place traps early (July or early August) to improve chances of success.  Once the yellowjackets have found the ripened fruit, the traps will be of little benefit. 

Applications of insecticides to grapevines are of very limited benefit and difficult to use because of harvest waiting intervals.  Yellowjacket nests in the ground or in walls can be destroyed by placing an insecticide dust in and around the nest entrance during the night.