Forest Pest Insects in North America: a Photographic Guide

Woolly elm aphid

Eriosoma americanum (Riley) (Hemiptera: Aphididae; Eriosomatinae)

Orientation to pest

Woolly elm aphid, Eriosoma americanum (Riley), is a native insect in North America whose primary hosts are American elm (Ulmus americana L.) and secondary, summer hosts are serviceberry (called saskatoon in Canada) and other species of Amelanchier spp. This aphid flies to elm in the fall where it mates and lays overwintering eggs. These hatch in the spring and nymphs feed on the edges of young elm leaves, causing them to roll inward and form a gall over the colony. In early summer, winged-forms migrate to Almelanchier species where they form colonies on the roots. Two other species of Eriosoma may also be found on elm, E. lanigerum (Hausmann) that causing terminal shoots to form rosettes and E. rileri Thomas, which forms woolly clusters on limbs and trunks. This aphid is a minor pest on Amelanchier alnifolia (Nutt.) Nutt., which is a fruit crop in Manitoba, Canada.

Hosts commonly attacked

American elm (U. americana) is the primary host and species of serviceberry (Amelanchier) are the alternative hosts.

Distribution in the USA

Woolly elm aphid is widely distributed throughout the eastern United States and Canada in the range of elm and serviceberry species.

Images of woolly elm aphid

Winged adult of woolly elm aphid Government of Alberta • Agriculture and Rural Development 300x268
Stem of serviceberry infested by woolly elm aphid Whitney Cranshaw, Colorado State University, 768x512 / 1536x1024
Figure 1. Winged adult of woolly elm aphid
Elm leaf galled by woolly elm aphid Steven Katovich, USDA Forest Service, 768x512 / 1536x1024
Figure 2. Elm leaf galled by woolly elm aphid Figure 3. Stem of serviceberry infested
by woolly elm aphid

Important biological control agents related to this pest species

Given this aphid's native status and limited damage, little is known about its natural enemies. In North America, some predators have been observed feeding on it, including the mirid Saileria irrorata Henry and the coccinellid Scymnus brulleri Mulsant.

Web links for information on woolly elm aphid