Boxwood leafminer, Monarthropalpusi flavus (Diptera: Cecidomyiidae), is the most serious insect pest of boxwoods. This small fly is native to Europe and widely distributed throughout the United States. The leafminer causes serious damage and heavily damaged plants will become quite unattractive. The larvae feed between the upper and lower leaves, which causes blistering and discoloration.
Both littleleaf boxwood, B. microphylla and common boxwood, B. sempervivens, are commonly attacked, but there is resistance found in individual varieties of both species. Common cultivars with reported resistance are ‘Handworthiensis’, ‘Pyramidalis’, ‘Suffruticosa’ and ‘Varder Valley’. Buxus microphylla var. japonica has also exhibited resistance to the leafminer.