A moderately common pest problem observed on hawthorn trees in May and June is the hawthorn leafminer, Profenusa canadensis. The leafminer is the larval stage of a sawfly. The larvae live inside the leaf causing the leaf tips to turn brown. Leaves appear to be diseased or damaged by frost. However, frass and at certain times even the larvae can be seen between the upper and lower epidermis by holding the leaves up to the sun.