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Steven Frank & James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

Boxwood leafminer, Monarthopalpus flavus (Shrank), Cecidomyiidae, DIPTERA

General Information

The boxwood leafminer is the most commonly reported pest of boxwoods in North Carolina. Accidentally introduced from Europe, this small fly seems to prefer American boxwood, although English and Japanese boxwoods are also susceptible.

Boxwoods infested with this leafminer develop blisters on the lower leaf surface. Infested leaves are usually smaller, off-color and drop sooner than healthy leaves. Heavily infested boxwoods usually have sparse foliage and poor color. Shrubs are generally not killed by leafminers.


Adult leafminer flies emerge over a two-week period in early spring just after the boxwoods have put out their new growth (about the time weigelas bloom). These flies are like tiny, orange mosquito-like (about 1/8 inch long) insects which swarm around or cling to boxwoods. After laying eggs in the leaf tissue, the flies die. There is one generation per year.

Tiny, whitish maggots hatch and feed inside the leaf. As they grow (up to 1/8 inch long), the maggots become bright yellow. Several maggots may develop in a single leaf. Their feeding induces the formation of blisters on the lower leaf surface inside of which the maggots develop for about a year. Very early the next spring, the blisters form a thin, translucent spot called the window, and the maggots develop into orange pupae. Fully developed pupae wriggle through the windows and hang down from the underside of the leaf. Soon adult flies emerge from the pupae to begin a new generation.


One of the pesticides listed in the table can be applied just as the boxwood leafminer flies appear in the spring. The flies emerge just after the new growth appears on boxwoods in April. At other times of the year, use a systemic such as Merit, Marathon, Tristar or Acelepryn as soil drench or soil injection. For the latest chemical recommendations, see the North Carolina Agricultural Chemicals Manual. Other homeowner lawn and garden products may be helpful. English boxwood seems less affected and Ohio reports 'Suffruticosa,' 'Pendula,' and 'Argenteno-variegata' as less susceptable.   Consult the labels and your local Cooperative Extension agent.
Pesticide (Trade Name) and Formulation TradeName Labeled Location Signal word IROC MOA Group Compatible with beneficials
†abamectin Avid G, L, N Caution 6 Yes
*acephate Orthene L Caution 1B No
acetomiprid Tristar G,N,L Caution 4A Yes
†azadirachtin Azatin G,N,L,I Caution 18B Yes
†bifenthrin Talstar G,N,L,I Caution 3 No
chlorantraniliprole Acelepryn L [none] 28 Yes
dinotefuran Safari G,N,L,I Caution 4A Yes
*†malathion malathion L Warning 1B No
imidacloprid Marathon II G,N Caution 4A Yes
*imidacloprid Merit L,I Caution 4A Yes
†permethrin Astro (Some homeowner insecticides may also contain permethrin or bifenthrin.) G,N,L,I Caution 3 No
†pyriproxyfen Distance G,N,L,I Caution 7C Yes
†spinosad Conserve G,N Caution 5 Yes
* Suitable for home use.
†Spray when adults are flying.

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service

Written by J.R. Baker April, 1994. Lightly revised 1998 by S. Bambara & S.Frank 2011.

Web page last reviewed January, 2011 by the webperson.