Leaf miners are a diverse group of insects which includes some flies, beetles, moths, and sawflies. Leaf miners live and feed between the upper and lower leaf surfaces. The shape of their mines is often characteristic and helps to identify the pest. This is the holly leaf miner. The insect that causes the damage is the larva of a tiny fly.
The boxwood leaf miner is also a delicate fly. Adult females, like this one, insert their eggs through the epidermis of new leaves. After hatching, the maggots feed within the leaves, causing unsightly blisters to appear. It is not uncommon to find half a dozen maggots per leaf. Though infested plants are rarely killed, they become sickly and unappealing.
A systemic insecticide, one that is absorbed into the plant, is necessary for effective control.
Winding tunnels indicate the presence of columbine leaf miner. This tiny leaf miner maggot seems to wander as it feeds.
The adult locust leaf miner is a small yellow and black beetle. The mines of their larvae seen here on the right are sometimes responsible for turning entire black locust trees brown in mid-summer. The adults are pests as well. Their feeding damage is mainly noted on black locust but many plants including dogwood, elm, oak, and apple may also experience some damage.
Yellow or brown tips on arborvitae indicate the presence of a small leaf mining moth known as the arborvitae leaf miner.
Arborvitae leaf miner caterpillars are only 1/5 inch long when full grown. They are so small that they can feed and complete their development inside the narrow arborvitae leaves. Infestations of this and many other leaf miners can be controlled most effectively with a systemic insecticide.