Amber-marked Birch Leaf Miner

The insect called the amber-marked birch leaf miner [Profenusa thomsoni (Konow) (Hymentoptera: Tenthredinidae] was introduced, possibly from Europe, into the northeastern United States in the early 1900s. Since then, it has become established throughout many parts of Canada, and was first reported in Edmonton, Alberta in the early 1970s.

In 1996, the birch leaf miner was first reported in Anchorage. The pest was probably introduced through imported ornamental birch. The birch leaf miner successfully “switched” tree hosts, and has now spread to native Alaskan birch. Intense outbreaks with noticeable defoliation have been a yearly occurrence in the Anchorage Bowl, and to some degree in the Mat-Su Valley. The birch leaf miner was detected in Fairbanks in 2002, but so far, has not been seen in Southeast Alaska. Hardest hit have been urban paper birch (Cover photo); birch in forest settings are less affected.

This brochure describes the life history and life stages of the birch leaf miner and presents homeowners with guidelines for minimizing damage to ornamental and native birch.

Life History:

Birch leaf miners spend the winter in the prepupal stage (brownish cocoons) in the soil beneath defoliated birch. Pupation occurs in the summer and the adult sawflies (almost always females) emerge in early July depending upon temperature and humidity. Adult emergence may last for more than a month. Eggs are deposited singly in slits cut in the central area of young leaves. Larvae feed on the tissues between the leaf surfaces (Figure 1). Young larvae feed singly. As the individual larval mines increase in size, they coalesce and form large, hollowed-out brown areas in the leaf (Figure 2). As many as 20–40 larvae may be found feeding in one leaf. Mature larvae chew their way out of the leaf and drop to the ground. They enter the litter layer, form small earthen cells, 2.5 to 5 cm below the soil surface. There they spin papery, brown cocoons. There is one generation of ambermarked birch leaf miners per year (Figure 3).

Description:

Mature larvae are somewhat flattened, yellowish white, and are about 6 mm long. Adults are black and about 3 mm long. Adult populations are almost totally comprised of females.

Damage Caused:

The most obvious sign of infestation is severe browning and distortion of foliage beginning in early August. Damage appears to be more serious on open-grown ornamental birch than on birch in forest stands. Heavily defoliated trees may be more susceptible to attack by other insects and pathogens. Tree mortality as a result of birch leaf miner defoliation has not been observed in Alaska.

Guidelines for Reducing Damage:

It is important to insure that birch growing in urban settings have the best possible growing conditions. Care should be taken to avoid injuring the roots, either mechanically or through soil compaction. Soil should neither be placed on top of nor removed from the area beneath the crown of the tree. Birches are very susceptible to drought conditions, especially in urban areas. In order to avoid moisture stress, adequate water should be provided to the trees, at least once a week, throughout the growing season. Spring fertilization also helps to promote tree vigor and to minimize the effect that defoliators such as leaf miners might have on a tree. The Cooperative Extension Service should be consulted for specific information on the type and amount of fertilizer to be applied.

Alternatives: When leaf miners are sighted, several alternatives are available for their control:

• When leaf miner populations are low, some limited defoliation may occur but most trees will be minimally affected as the damage occurs late in the growing season. The raking and disposal of leaves and litter beneath the defoliated tree in the fall will remove many of the overwintering prepupae and help minimize leaf miner defoliation the following year.
• Early chemical control can greatly reduce subsequent damage. Prevention of egg-laying and larval feeding may be accomplished using systemic insecticides. Systemic insecticides are longer lasting, but take longer to become effective and require extreme caution in their application. These systemics can be applied either to the foliage or to the soil to be absorbed through the roots and transported later to the foliage. Check with your local Cooperative Extension Service office for insecticides that are currently registered for birch leaf miner control.

Photography Credits

Figures: Bugwood, www.bugwood.org, The University of Georgia Cooperative Extension Service, Tifton, GA.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Since approved uses of a pesticide may change frequently, it is important to check the label for current approved and legal use.
Follow recommended practices for the disposal of surplus pesticides and pesticide containers. Mention of a pesticide in this publication does not constitute a recommendation for use by the USDA, nor does it imply registration of a product under Federal Insecticide, Fungicide, and Rodenticide Act, as amended. Mention of a proprietary product does not constitute an endorsement by the USDA.

Amber-marked Birch Leaf Miner

by Ed Holsten, Research Entomologist, USDA Forest Service, Alaska Region, State and Private Forestry.

Additional information on this insect can be obtained from your local USDA Alaska Cooperative Extension office, Alaska State Forestry office.

Please see this link for up-to-date contact information for our professional staff and office locations.