Phytomyza ilicis

Holly leafminer damage. Photo: Daniel Herms, The Ohio State University, Bugwood.
Scientific Name: 
Phytomyza ilicis
Common Name: 
Holly Leafminer
Growing Degree Days (GDD's): 
245–600 GDD's, Base 50F, March 1st Start Date (Source: Robert Childs, UMass Extension.); 246-448 GDD's, Base 50F, March 1st Start Date (Source: Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
English holly (Ilex aquifolium) *Only reproduces on this host.
Insect Description: 

This particular species of holly leafminer was introduced from Europe and feeds only on Ilex aquifolium. Holly leafmining flies on other species of holly are therefore different species of insects. This species is now known both to the eastern and western United States. The damage this species causes, as well as its biology, are both similar to our native holly leafminer (P. ilicicola) which is discussed elsewhere in this guide. The main difference in the life cycle is that the European holly leafminer lays its eggs in the midvein of the leaf. The young larvae then tunnel in the midvein until the fall. One generation occurs per year. Larvae overwinter in their leaf mines, pupating in March or April. Over an approximately 6 week period, the adult flies emerge in the spring. This may begin after new leaves have formed on the host. Adults are tiny, black flies approximately 1/8 inch in length. In approximately 10 days, adult females lay their eggs in the leaf midveins. Larvae are yellow maggots and up to 1.5 mm. when fully grown. Larvae feed slowly, and current year's mines may be easily overlooked (Johnson and Lyon, 1991).

Damage to Host: 

Feeds and reproduces only on Ilex aquifolium. Damage is similar to that of the native holly leafminer but larvae of the European holly leafminer mine the midveins of the foliage until late fall. In heavy infestations, every leaf may be mined. Plants may drop leaves prematurely (especially when several mines are found per leaf) and remain thinly crowned until new growth begins the following spring. 

Monitoring: 

Monitor for mines in the late summer, and again for expanding mines beginning in March. Adult flies may be seen on terminal leaves in May through June. 

Cultural Management: 

Pick and destroy mined leaves before March/April. 

Natural Enemies & Biological Control: 

Natural enemies (parasites and predators) of the European holly leafminer have been detected in both the US and Canada. Sources note that natural enemies may keep populations of this insect below damaging levels, particularly if no chemical management (or reduced risk chemical management) is used. Parasitoid wasps such as Chrysocharis gemma, C. pubicornis, Cyrtogaster vulgaris, Opius ilicis, and Sphegigaster flavicornis have been recorded as biological controls or natural enemies of the European holly leafminer (Invasive Species Compendium; CABI).

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bifenthrin (NL)

Carbaryl (L)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyromazine (NL)

Diflubenzuron (N)

Dinotefuran (NL)

Fenpropathrin (NL)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Permethrin (L)

Pyrethrins+sulfur (NL)

Spinosad (NL)

Notes: 

Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection) acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), diflubenzuron (soil drench), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: September 27, 2024. To check current product registrations in Massachusetts, please visit the MA Department of Agricultural Resources Pesticide Product Registration page and click on "Search Pesticide Products Registered in Massachusetts - Kelly Solutions".