Pest profile

Boxwood Leafminer

Monarthropalpus flavus · Diptera: Cecidomyiidae[2]

Swarms of tiny orange midges around boxwoods in spring, and blistered, yellowing leaves later, point to the boxwood leafminer.[1]

Adult boxwood leafminer, a delicate orange mosquitolike gall midge with clear wings, on a leaf
Adult boxwood leafminer, a delicate orange mosquitolike gall midge with clear wings, on a leaf. (c) Katja Schulz, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are delicate, mosquitolike flies about 1/10 inch long with long legs and antennae and a reddish to yellowish orange body.[1]
  • Larvae are legless maggots up to 1/8 inch, green, orange, whitish or yellow, hidden inside leaves.[1]
  • After emergence, empty whitish pupal skins stick out of small holes under the leaves.[1]

Where it lives

It feeds only on boxwoods (Buxus species).[1]

US map: public records from 20 states since 1990 (GBIF).

Biology and life cycle

Adults are present for about two weeks in spring, usually April, and females lay up to about 20 eggs per leaf.[1]

Eggs hatch in two to three weeks, and larvae feed through summer, overwinter and pupate inside the mine.[1]

There is one generation a year.[1]

Damage and signs

  • Mines start as pale spots on the upper leaf and become brownish swollen blisters underneath.[1]
  • Infested leaves are yellower and smaller; heavy infestations brown and drop leaves and cause branch dieback.[1]

Health risk

It damages only boxwood; UC IPM notes nothing about people.[1]

Control

Prevention

Keep boxwoods vigorous with good care, especially adequate soil moisture in the dry season.[1]

Consider resistant boxwoods such as Buxus microphylla var. japonica, 'Green Pillow' or 'Vardar Valley'.[1]

Sanitation

Rake up fallen boxwood leaves in fall and winter, and clip off lightly mined leaves.[1]

Pesticides

For valued plants, UC IPM lists dinotefuran or imidacloprid soil drenches in late winter or spinosad sprays in spring, applied after bloom because all three harm bees.[1]

Common questions

What are the little orange flies around my boxwood?
Probably adult boxwood leafminers, which appear for about two weeks in spring.[1]
Can I avoid the problem?
Planting resistant boxwood varieties is one of the most reliable options UC IPM lists.[1]

Sources

  1. University of California Statewide IPM Program, “Boxwood Leafminer (Pests in Gardens and Landscapes).” ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/boxwoodlfmin.html (accessed 2026-10-06)
  2. iNaturalist, “Monarthropalpus flavus taxon page (order and family).” www.inaturalist.org/taxa/467578 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.