Birch Leafminer
Fenusa pusilla |
| USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus. |
This introduced sawfly attacks all species of birch, but gray birch and paper birch are most susceptible. Defoliation by the birch leafminer is unsightly and may predispose trees to attack by the bronze birch borer. Defoliation also permits excess heating of the soil by direct sunshine. The resulting high temperatures can kill roots and lead to birch dieback.
The flattened, yellowish-white larvae are about ΒΌ of an inch long with black spots on the underside of the thorax and on the first abdominal segment. Larvae feed on tissue between the leaf surfaces, creating irregular brown, dry patches on the leaves. Full-grown larvae chew exit holes in the leaves and then drop to the ground, where they hibernate in the soil. Pupation occurs during April. First generation adults emerge in early May. There may be three or four generations per year.
Damage; inner leaf tissue may be completely destroyed (note the appearance of the black frass in mines) larva in leaf on gray birch
Photo by E. Bradford Walker, Vermont Department of Forests, Parks and Recreation
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Damage; trees attacked appear off-color
Photo by Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation
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