These tiny insects feed on the strawberry near the cap, or calyx. Light feeding injury may simply cause the seeds on the berries to be more prominent. More severe injury will cause fruit bronzing. If the skin of the fruit is severely scarred, it cracks, especially near the cap. On early varieties, later sets of berries are more likely to be affected than king berries.
Later varieties are more likely to be affected than early ones.
You should suspect thrips injury if you have seedy berries, and bronzed or cracked fruit. Using a handlens or microscope you may observe the insects feeding just under the calyx. However, once the fruit is severely injured, the thrips may move on to new sites. Experience in other parts of North America has suggested two thrips per fruit at the early maturity stage is enough to cause significant problem. Adult thrips are thought to blow in from the USA on air currents.