Native to the United States, the holly leafminer (Phytomyza ilicicola) is the most damaging insect pest of holly in the eastern United States.  The holly leafminer damages a number of holly varieties by feeding between the upper and lower surface of the leaf tissue.  These mines ruin the aesthetics, may cause partial defoliation, and can lead to early leaf drop in heavy infestations.  Damage is also created when the female adults pierce the leaf tissue to deposit eggs.  Feeding of the sap occurs at these wounds and causes leaf deformities.

Susceptible Hosts
Holly leafminer is a pest that affects many varieties of holly including American holly (Ilex opaca), English holly (Ilex aquifolium), dune holly (Ilex cumulicola), inkberry (Ilex glabra), deciduous holly (Ilex dicidua), Japanese winterberry (Ilex serrata), winterberry (Ilex vericillata), and yaupon holly (Ilex vomitoria).

Pest
Phytomyza ilicicola

Symptoms
* Initial symptoms appear as short (1/2 inch), slender mines in the leaves.
* The leaf mines become wider, and eventually may cover the entire leaf in yellow serpentine mines, and/or brown blotches.

Signs
* The eggs are very small, white, and oval.
* The larvae are pale-yellow, legless, and about 1.5 mm in length
* The pupae are 2mm in length, and reddish-brown in color with tapered, blunt ends.
* The adult is a black and gray fly that is about 2.5 mm in length.

Life Cycle
* Pupation occurs in early spring (March/April)
* The adult flies emerge over a six-week period beginning in May, as the leaves appear on holly.
* After mating occurs, the female pierces the underside of the young leaves, which causes tiny, green blisters, and deposits her eggs.

* Eggs hatch in about 4 days, and the larvae begin to feed on the leaf tissue between the upper and lower leaf surface, creating new mines.

* Over wintering occurs in the leaf mines.

Distribution
The holly leafminer is found along the East Coast and as far west as Ohio and Alabama.

Properly timed soil applications of Xytect, Transtect, or Lepitect are extremely effective against leafminers.   When possible, American hollies should be grown in partial shade.  Trees in full sun are usually more heavily damaged by this pest.  Spray with Orthene, Xytect or Transtect at 350-660 GDD to control large populations of adult flies and again at 1200 – 1400 GDD to control larvae. 

Sprays to control adults will reduce adult feeding on leaves and also control oviposition punctures in the leaves.  All of these products will provide good trans-laminar movement to control larvae inside the foliage. 

Soil applications are extremely effective against this pest.  Orthene foliar sprays will provide translaminar movement and provide good control of larvae inside the foliage.  Xytect and Transtect can also be applied as foliar sprays and will provide translaminar movement and good control as well.  For small to medium size shrubs or hedges consider using lower dosage rates.

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