Petiolegall Aphid

Petiolegall Aphid (Pemphigus species) - Found on cottonwoods and poplars.  The feeding of the aphid on the petiole (stalk of a leaf) causes the leaf to develop a marble-like gall feature.

Marble-shaped Petiolegalls on the petiole or leaf stalk of a cottonwood
Photo: Hunter Cathcart



Petiolegall cut open showing a gray mass of aphids
Photo: Hunter Cathcart

Petiolegall aphids do not cause significant damage to the tree.

Winged adult aphids lay eggs in bark cracks on cottonwoods and poplars in the fall. In spring the eggs hatch and the nymphs (immature aphids) feed on the developing leaf petioles. The feeding causes the plant to produce a gall structure around the developing aphids. As the overwintered stage becomes full-grown, they produce young which will remain inside the gall structure until full-grown. The young developing in the gall will have wings. The galls open along a slit and the winged aphids leave the plant in late June or July. The photos above were taken on July 11, 2007. The winged aphids leave the gall and fly to a summer host. The summer host are the roots of various annual plants such as sugarbeets, lambsquarters, and lettuce. Several non-winged aphid generations may be produced on the roots of the summer hosts. At the end of summer sexual winged stages are produced that will fly back to the winter host (a cottonwood tree), mate, and lay eggs.

Controls for petiolegall aphids are usually not necessary and have not been developed for gall-forming insects on trees. If a control is desired, a non-insecticide application of Dormant oil can be sprayed on the bark of poplar trees to smother the overwintering eggs.

This information was obtained from Colorado State University Cooperative Extension.

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.