This boxwood leaf has been broken open to show the larvae feeding. Infested leaves often drop early.
Exuviae of an emerged adult leafminer.

The boxwood leafminer is a serious pest of boxwood, Buxus spp. It was first reported as a pest in the United States in 1910. Now it is found across the United States wherever boxwood grows.

It's the most serious pest of this evergreen plant. All varieties of boxwood are susceptible, but the slower-growing English varieties are less susceptible than the American cultivars. The leafminer feeds between the upper and lower sides of the leaf. This feeding causes blisters on the underside of the leaf. Leaves infested by this pest become yellow and smaller than a normal leaf. In fact, plants that are severely infested appear completely unhealthy.

Photos: Brian Kunkel, University of Delaware, Bruce Watt, University of Maine, Eric R. Day, Virginia Polytechnic Institute, State University, Bugwood.org