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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