Leaf miners are a type of insect that eat the mesophyll layer of the leaf. The elm leafminer's common name is a sawfly. The adult female sawfly lays eggs on the bottom side of the leaf. These eggs hatch and the larvae burrow through the mesophyll layer of the leaf creating tracts as they eat. The leaf eventually falls to the grown in the fall, or the leaf is killed by excessive leafmining and falls to the ground. Once the leaf is on the grownd, the larvae crawl out and burrow about one inch under the top soil. The larvae form a cacoon and wait out the winter underground. In the spring the larvae hatch from the cacoon and dig their way out of the soil to emerge as an adult sawfly. The adult saw fly lays more eggs and the life cycle continues.
The majority of damage done by the leafminer is asthetic;the overall damage to the leaf is not life threatening ot the tree, but the leaves can die if too much of the mesophyll is eaten. There are insectasides available for the soil, to kill the sawfly cacoons, or for the leaves of the tree, to kill the eggs. Insectasides are expensive and time consuming. Therefore finding trees that are less likely to be attacked by sawflies is the best solution to this problem.