Grape Blossom Midge, Contarinia johnsoni Felt (Diptera: Cecidomyiidae)
The grape blossom midge is a small fly that lays its eggs in unopened grape flower buds. Small maggots, or larvae, hatch and eat the inner portions of the flower. Buds affected in such a manner are incapable of forming a flower and thus a berry. Infested flower buds are slightly enlarged and lower portions are red. This is in contrast to normal flower buds, which are completely green. The grape blossom midge has one generation per year; it passes the winter as a full-grown larva.
This midge is most often present on vines near brushy or wooded areas, and it rarely causes much damage.
Current pesticide recommendations may be found HERE