Boxwood Leafminer – Monarthopalpus flavus

Boxwood Leafminer: Appearance, Territory, Damage and Life Cycle

Latin Name: Monarthropalpus Flavus

Appearance: The most damaging insect pest of boxwood is the boxwood leafminer. Boxwood leafminer is a significant pest of a popular landscaping plant. This insect’s annual feeding may severely disfigure bushes in some regions of Michigan, when injured leaves shed in the middle of summer. The insect is actually a fly, but its larval phase, which resembles a little yellow worm (maggot), causes the leaf damage by feeding between the top and lower layers of the leaf.

Hosts Plants: The most damaging insect pest of boxwood is the boxwood leafminer.

Territory: Europe

Damage Insect Cause: The larvae continue to eat when the temperature heats up in the spring, creating apparent “blisters” on the leaf that, when taken off, reveal the little yellow maggots. A cracking sound is made by plants that are severely damaged. Small pinprick-sized emergence holes will occur on the underside of the leaf as the adult flies emerge. Although boxwood leafminer is a seasonal concern in some areas, it has been prevalent in west Michigan for several years. Some boxwood cultivars are more resistant than others, so selecting the most resistant kinds is usually a good idea.

Life History and Habits: Boxwood leafminer larvae overwinter as half-developed larvae in leaf blisters. When the weather warms up in the spring, the larvae become active. In May, the adults force the pupal skin out of the mine, where it hangs for a few days after the fly emerges. Adult flies congregate around boxwoods about the time the Weigelas bloom. Female’s mate and lay their eggs on the undersides of the leaves when the new growth of the boxwood emerges in the spring. In 14-21 days, the eggs hatch into the larval stage (a maggot) and consume for the rest of the summer. After that, the larvae develop into orange pupae, which darken before the adults emerge. Every year, a new pest generation emerges.