Injured fruit were first reported in Adams county during 1998. Sawfly larvae resemble caterpillars, but have prolegs on each abdominal segment. Sawfly overwinter as larvae in the soil and have only one generation per year. Adults emerge during late pink and early bloom. Eggs are laid on the calyx end of developing fruit.
Young larvae feed along the surface of the fruit and leave a winding feeding scar on the surface.
These apples usually remain on the tree, and the presence of the scars can reduce fruit value. Older larvae bore deeply into one or more fruit, usually causing mid-season fruit abortion. Monitoring and management White sticky rectangle traps should be placed at one per 3 to 5 acres along the orchard periphery at pink on the south sides of trees at 5 to 6 feet above the ground. Treatment thresholds are 5.5 flies per trap by petal fall if no prebloom insecticide has been applied or 4.7 flies per trap with a prebloom insecticide. An application of an organophosphate insecticide as soon as pollination is complete is the best control tactic for orchards with a history of this sawfly.