Leaf Miners are insect larvae that eat leaf tissue within the leaf itself, that is between the upper and lower leaf surfaces. These larvae are common in Colorado and are the offsprings of various insects including certain species of flies, moths, sawflies, wasps, and beetles. Leaf Miners attack a wide range of trees including but not limited to birch, boxwood, cypress, magnolia, oak, and others. As the Leaf Miners feed on the interior of the leaf, outlines of tunnels and blisters can be seen. As the insect matures, it consumes ever-larger sections of the leaf leading to yellowing, browning, and eventually leaf death. They create winding tunnels that are clear, except for the trail of black fecal material (frass) left behind as they feed. Leaf Miner species can often be determined by the shape of tunnels and droppings.
Adults are black to gray flies with yellow stripes and clear wings 1/10 inch in length. Larvae are worm-like maggots (1/3 inch) which are often pale yellow or green in color. Leaf Miners larvae overwinter in soil beneath host trees. In April, pupation occurs and adults emerge and mate, laying eggs on the underside of host leaves. The larvae hatch and enter the interior of the leaf, eating for approximately 2-3 weeks. The larvae then drop into the soil below the host to pupate and repeat the life cycle. Several generations can occur each year.
Healthy trees can withstand some degree of Leaf Mining insect larvae, but stressed trees may be more susceptible to catastrophic damage. Walker Tree Care has a plant healthcare department that is trained and equipped to deal with infestation and prevention of all species of Leaf Miners.