University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Boxwood Leafminer
Monarthropalpus flavus

Boxwood leaf miner damage
Boxwood leaf miner damage
2 (1 = rare 5 = annual)
2 (1 = very little damage 5 = plants killed)

Plants Affected
Damage starts to appear about midsummer as yellow spots. Winding tracks (mines) through the leaves are at first whitish, turning brown as they age. Leaves may fall off early. In addition, heavy infestation can cause plants to look thinned out; even killing branches. Heavy infestation make the plants more prone to winter kill and diseases.

Life Cycle
These miners over winter as a partially grown larvae in the boxwood leaves. Warm weather in the spring helps the larva finish growing and become a pupa. A few days before the adult emerges, the pupa wiggles out of the mine to the surface of the leaf. A fly emerges from the pupa case. The flies are about the size of a gnat. After mating, females lay slightly more than two-dozen eggs inside the upper tissue of new leaves. Several weeks later, the larvae emerge and begin feeding. It is not uncommon to find multiple larvae in the same mine. Larvae grow slowly through the summer.

There are few natural predators but there are boxwoods known to be resistant to this insect.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic