Farmers and gardeners who grow blueberries may notice damage to the developing berries caused by the cranberry fruitworm. The cranberry fruitworm moth lays eggs on green berries and after hatching the larvae burrow into the fruit and eat the pulp. Larvae will move from berry to berry, feeding and leaving behind frass (excrement). Most people will not notice the fruitworms which are inside the fruit but the frass they leave behind is easily visible on the fruit clusters.
The good news is this pest usually causes very minor damage, only infesting a small percentage of berries. By the time berries are harvested the damaged, infested fruit has dropped off the bush. Large acreage conventional growers will often spray an insecticide at petal fall to control these pests because they are already spraying for other pests and diseases. For small growers treatment is not required as the damage in most cases is minimal. In the series of photos below, the fruitworms have already done their damage and are pretty much done. They will pass the rest of the year as larvae on the ground.
For more information:
Cranberry fruitworm fact sheet – North Carolina State University