Allium leaf miner also called onion leaf miner has been detected and confirmed in Lancaster County PA recently. This is a new pest in the U.S. which affects all onions, chives, shallots, garlic, but the most sensitive is leeks. This pest can also affect ornamental Allium species, and weeds. Adult female flies puncture leaves on the edges and lay eggs. Larvae move through leaves to the sheath and bulbs where they pupate, and overwinter as brown pupae. Punctures and leaf mines are wounds through which bacteria and fungi can invade. See the Penn State and Cornell pest alert for more information and references: PestAlert-Allium Leaf Miner
NFG April 17, 2017
