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European Pine Shoot Moth - Rhyacionia buollana

by Rayanne D. Lehman

The European pine shoot moth is a serious but sporadic pest of ornamental, Christmas tree, and timber pines. Damage, including distorted growth and misshapen trees, may be misdiagnosed as another shoot borer or as a disease.

Hosts and Distribution: The European pine shoot moth infests many species of pine, pre­ferring Austrian, red, and Scotch. This introduced pest was first detected on Long Island, New York, in 1914, where it was severely damaging Scotch pine. Repeated introductions of infested nursery stock from Europe, particularly Holland, are thought to be responsible for the nine-state distribution revealed during a 1915 survey. Because it was quickly rec­ognized as a serious pest of native red pine, growers in Canada significantly reduced the number of red pines they planted.

This borer is widely distributed in the northeastern states west to Minnesota, and in Oregon, Washington, and southern Canada. Pines in nurseries and Christmas tree planta­tions are most frequently infested. Trees in closed stands and those taller than 8 meters are generally not damaged. 

Identification: Adults are medium-sized moths with wingspans of 18-22 mm. Their orange-red forewings have several irregular silver bars. Superficially the moths resemble several other species of lepidopterous pine pests, especially the smaller, closely related Nantucket pine tip moth (Reg. Hort. Entomology Circular 162). Like some other shoot-boring moths, European pine shoot moths may be mistaken for dried and damaged buds or bud scales.

Larvae are pale yellow-brown to brown and have black head capsules and thoracic shields. At maturity they are about 13 mm long.

Life History and Habits: Adults emerge from pupation sites in new-growth shoots between mid-June and mid-July, at approximately 700-800 growing degree days (base 50°F) (Mich. St. Univ. 1996). Male moths emerge before females, and when conditions are favorable, adults can fly several miles. These moths are most active at dusk when temperatures are about 70°F. They cause no direct damage to trees. Females deposit up to 50 small, oval, flattened eggs, singly or in small groups. Eggs are laid for several weeks on needle sheaths, needles, and buds of the new growth anywhere on the tree. Initially, eggs are cream-colored, but change to orange-brown and resemble the buds and bud scales Before hatching in about 10 days, they develop a greyish color - much like that of the needle sheaths.

First-instar larvae move about on the new shoots and settle to construct silken webs between the needle sheaths and the bark on the current year's shoot.  They bore through the fascicles and into the needles to feed, causing resin to soak their webbing. By late summer, larvae move out of the needles and hollow out newly formed buds to create overwintering chambers. Resin-coated silken webs also cover openings to these chambers, protecting the larvae inside.

Larvae remain dormant inside the overwintering chamber from late August until tree growth resumes the following spring. After several days of temperatures above ~ or between 20-200 growing degree days (base 50°F), they exit the buds and enter newly expanding buds or shoots to complete feeding. This stage of feeding usually occurs in late April and causes the most significant damage - a single larva may damage many shoots.

If suitable buds are not found, larvae move upward in the tree, sometimes reaching and destroying the leader. Feeding is completed by mid-May, when pupal chambers are creat­ed inside the shoots. In about 3 weeks the moths emerge, frequently leaving the empty pupal cases protruding from the buds. There is a single generation each year:

Damage, Detection, and Diagnosis: Three different types of damage may occur on shoots anywhere on the tree: newly hatched larvae can kill individual needles, particularly around buds; intermediate larvae kill buds in preparation for overwintering; and mature larvae kill developing buds and elongating shoots. Damage by the mature larvae, which occurs in spring, is the most significant and results in production of numerous adventitious buds, leading to a type of witches'-broom.

As a result of European pine shoot moth feeding, trees will have dead, stunted shoots that may look as though they are infected with Sphaeropsis (Diplodia) shoot blight.  The Nantucket pine tip moth causes similar damage but is appreciably smaller.

Shoots that are damaged, but not killed, will continue to grow into a characteristic "S" shape, known as a posthorn. Infested trees are frequently bushy and distorted and may develop multiple leaders, which require intensive corrective pruning to restore a desirable shape.

Detection of this pest may be difficult. In late summer or fall, look for resinous masses concealing single larvae inside hollowed-out buds. In spring, scout for dying buds and shoots containing larvae. Commercially available pheromone lures are useful for monitor­ing male activity. Growers using these lures can accurately time their control measures against newly hatched larvae in summer.

Control: Shearing trees after mid-July will remove many eggs or young larvae on new shoot tips. Individual shoots containing mature larvae should be destroyed before mid-June, when adult emergence begins. Like Nantucket pine tip moth, this species is not able to survive extended exposure to extreme cold - temperatures below -20°F are lethal. The butt pruning of trees will remove overwintering sites below the insulating snow line. Dry weather and poor soil conditions are reported to enhance buildup of this significant pine pest.

Numerous species of native and introduced parasites and predators may keep popula­tions from reaching high levels. None, however, can rapidly reduce heavy infestations to acceptable levels, making chemical controls necessary when trees are nearing harvest.  Benyus (1983) suggests treatment when one of the following conditions exists: 10% or more of young trees are damaged, older trees have more than five injured tips per tree, or any amount of damage is found in the harvest year. Sprays directed against larvae can be effective twice during the life cycle - at egg batch or when overwintered larvae migrate to new shoots in spring.

Selected References

Benyus, J.M., ed. 1983. Christmas tree pest manual. U.S. Dep. Agric. For. Serv. No. Cent. For. Exp. Stn. St. Paul, Minn. 108 pp.

Drooz, A.T., ed. 1985. Insects of eastern forests. U.S. Dep. Agric. For. Serv. Misc. Publ. 1426. Washington, D.C. 608 pp.

Johnson, W.T. and H.H. Lyon. 1966. Insects that feed on trees and shrubs, 2nd ed. Cornell University Press, Ithaca, N.Y 556 pp.

Michigan State University. 1996. Christmas tree insect forecast table. Mich. St. Univ. Coop. Ext. Crop Advisory Team Alert. 10(1): 5.

Pointing, PJ. and G.W. Green. 1962. A review of the history and biology of the European pine shoot moth, Rhyacionia buoliana (Schiff.), in Ontario. Proc. Entomol. Soc. Ont. 92:58-69.

 

REGULATORY HORTICULTURE

Vol. 22, No. 2 (Fall 1996)

Entomology Circular No. 183

PDA, Bureau of Plant Industry