Fruits seriously injured by the insect's feeding and egg-laying activities fall to the ground or, if harvested, are culled out on the packing line. Lightly injured fruits, however, will occasionally appear on the market, especially in lower commercial grades. Early in the growing season, adult curculios puncture the skin of young fruits and eat out small cavities beneath. When these fruits become mature, the punctures appear as small, round russeted scars. When abundant, these injuries cause the apples to be badly deformed and misshapen.
More typical injury is produced by egg-laying punctures, shaped as crescent slits in the skin.
As the apples grow, the injured areas expand and by maturity are more or less shield-shaped russeted scars. In the fall, adult curculios of the new generation often feed on ripening fruits, mostly around the calyx and stem ends. These feeding punctures do not heal. They appear as small, dark-brown cavities which may permit the entrance of decay organisms. Causal factors Adult plum curculios are small, hard-shelled beetles with long snouts.