American sycamore is a magnificent native tree often found growing along streams and rivers. Although it thrives in rich, moist soils, its ability to survive stressful environmental conditions such as drought, heat, compacted soil, and pollution makes sycamore a popular tree in cities and residential landscapes. Often by the middle of summer and reliably by the month of October, sycamores just look sick. Their leaves have turned from verdant green to anemic yellow. This is not just Mother Nature preparing the tree for winter. This is the work of the dastardly sycamore lace bug. Since late spring many sycamores have had the life sucked out of them by thousands of these tiny insects.
We met relatives of the sycamore lace bug in a previous episode of Bug of the Week May 26, 2006, entitled “And may all your azaleas be white.” It is not unusual to find dozens of lace bug eggs, nymphs, and adults on the undersides of sycamore leaves. The adult lace bug is a beautiful insect. Its outermost wings are delicate with lacey veins, hence the name lace bug. These wings are not just adornment. They can be tilted like a shield to ward off the attack of a would-be predator like a lacewing larva or ladybug. As autumn ends, adult lace bugs find refuges beneath bark or under debris on the ground to spend the winter. In spring shortly after new leaves are formed, they return to the foliage, feed, and insert small black eggs into the leaf surface. A female lace bug can lay more than 200 eggs during the course of her lifetime.
The eggs hatch into tiny black nymphs festooned with rows of spines. Like their parents, lace bug nymphs have a beak that is inserted into the plant tissue to withdraw the liquid contents of the plant cells. The combined feeding of nymphs and adults results in many tiny white spots or “stipples.” These can be seen on the upper surface of the leaf. The lower surface of the leaf is a spectacle of nymphs and adults feeding and dashing about. They leave behind the spoils of their ongoing capers - shed skins, eggs inserted into leaves, and dark fecal spots. As numbers of lace bugs grow, stipples increase and sometimes coalesce in a way that makes the entire leaf appear yellow or bronze. If lace bugs and their damage are too great, the sycamore may simply drop its leaves and bring a premature end to the lace bug's shenanigans.
Information used in this episode came from Managing Insect and Mite Pests on Woody Landscape Plants: An IPM Approach by J. A. Davidson and M. J. Raupp. To learn more about the sycamore lace bug, please visit the following web sites.