The dispersal peak of the western flower thrips,Frankliniella occidentalis(Pergande), occurred during the spring grape bloom period and the insects were attracted to the flowers. The thrips oviposited in the young berries and eggs were dissected from the wounds. The insects were very prolific when 25, 75, and 100 adults were caged on Thompson Seedless clusters at either 0, 50, or 100% bloom. The thrips scarred the rachis, laterals, and berry pedicels of Thompson Seedless and Calmeria grapes but did not cause necrotic scars on the surface of the fruit. Clusters that supported up to 1,582 adults and nymphs did not have a greater amount of surface scars than non-infested clusters. Total berry to rachis length ratios indicated that exposure to thrips may have improved fruit set. Surface scars were mechanically induced with a platinum wire. The light halo around an ovipositional scar was unique to a deposited egg. The amount of ovipositional scars on Calmeria grapes was proportional to the number of thrips introduced on the clusters and the amount of time the clusters were exposed to natural infestations.