Monarthropalpus flavus

Box Tree Moth (BTM) (Cydalima perspectalis) has stolen the thunder of another non-native boxwood nemesis: Boxwood Leafminer (Monarthropalpus flavus, family Cecidomyiidae). However, the European expat remains a significant boxwood pest and should not be ignored.

Boxwood leafminer damage is already becoming apparent. However, the symptoms are highly variable and may be mistaken for winter injury, a “leaf blotch” disease, or something else. Birds seeking meat morsels in the form of leafminer larvae can produce an entirely different type of strange-looking damage.

The boxwood leafminer is a European import first reported in the U.S. in the early 1900s. The exact timing of its accidental introduction is not known, but it’s suspected the leafminer may have arrived in the U.S. as early as the 1600s when boxwoods were first planted in U.S. gardens.

The non-native boxwood leafminer (Monarthropalpus flavus) was accidentally introduced into North America from Europe in the early 1900s. It is now common on its namesake host throughout Ohio producing symptoms at this time of the year that may be mistaken for winter injury.

Swarms of boxwood leafminer adult flies are flitting around their namesake host. The delicate-looking flies belong to the same family (Cecidomyiidae) as gall midges.

I posted a BYGL Alert on Boxwood Leafminer (Monarthropalpus flavus) back in March noting that heavy oviposition observed last season presaged heavy leaf damage this spring. However, I neglected to report a possible odd side effect: heavily infested boxwoods going snap, crackle, pop.

It's common for boxwoods to emerge from the winter with yellow to brown foliage caused by a number of issues including winter injury and salt damage. However, the primary cause behind discolored boxwoods this spring is the predicted damage by boxwood leafminer.

Boxwood leafminer activity is already very evident on their namesake host in southwest Ohio. This does not bode well for 2020. As the midge fly leaf mining activity further delaminates the upper and lower leaf surfaces, symptoms may become apparent by the end of this season. They will certainly intensify next spring.

Participants in this week's Greater Cincinnati BYGLive! Diagnostic Walk-About were treated to an enormous swarm of boxwood leafminer adult flies flitting around their namesake host. The flies are a type of wood midge and belong to the same family (Cecidomyiidae) as gall midges.