Yellowjackets, Vespula spp.

Yellowjackets and certain other wasps may break open the skins of grape berries in order to reach the sweet contents. In the early part of the growing season these wasps are mainly predatory. Toward the end of the season the wasps' foraging behavior changes and the sugar content of the fruit increases. Although honey bees are sometimes seen on broken fruit consuming the juice, they are not responsible for the initial injury because their mandibles are not strong enough to puncture the fruit skin. Control measures can be directed against the overwintering yellowjacket queens by establishing bait stations containing an attractant and a pesticide in early spring. Destruction of nearby nests is helpful but difficult, because they are often located underground.  Control aimed at foraging workers in the preharvest period may help, will be limited by short residual life of available insecticides, and only the active workers will be affected.

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