The woolly elm aphid, Eriosoma americanum, females lay a single egg in the cracks and crevices of elm bark, where the egg overwinters. This generation of aphids lay their egg in the fall. Eggs hatch on elm in the spring as leaves are unfolding. A young, wingless female hatched from the egg feeds on the underside of elm leaf tissue. This female aphid matures and gives birth to 200 young, all females, without mating. These aphids feed, and the elm leaf curls around them and protects them. By the end of June, the curled leaf becomes very crowded and the aphids begin to spill out. Elms are the primary hosts of this insect. Winged migrants mature from the curled elm leaf and disperse to find serviceberry hosts, their secondary host plants. Another set of females is produced on serviceberry. These new females crawl to and begin feeding on the roots of serviceberry. Multiple generations occur on the roots of serviceberry through the summer. By the fall, a winged generation develops again (on the roots of serviceberry) and it is these individuals that fly back to their elm hosts to lay their single overwintering egg (Johnson and Lyon, 1991).
The damage to the elm host plant is mostly aesthetic. Woolly elm aphids cause elm leaves to curl around them. These leaves may turn reddish or brown in color as a result. Curled leaves become packed with aphids and cast skins, which may eventually spill out of the curled leaves in June. The generation that feeds on the roots of serviceberry may cause some damage during the course of their feeding to the roots. (Certain species of Amelanchier, while not native to Massachusetts, are severely damaged as seedlings by the feeding of these aphids on their roots. For example, Amelanchier alnifolia or saskatoon berry, is so severely fed upon by this insect that up to 85% of seedlings may be lost (Fry, 2001).) In managed landscapes, however, this insect is likely to be only of aesthetic interest, and may not require management intervention.
Visually monitor for curling in newly developing elm leaves.
There is potential for discouraging this aphid in a managed landscape by avoiding planting elm near serviceberry. However, winged individuals readily disperse in woolly elm aphid populations, and may be able to travel long distances to find their alternate host plants. Remove and destroy any newly developing elm leaves that are curling around these feeding aphids early in the growing season if practical or possible on smaller trees.
A tiny parasitoid wasp, Aphelinus mali, is a native natural enemy of aphids in the genus Eriosoma. Lacewings, lady beetles, and syrphid fly larvae are all predators of these aphids. Plantbug predators are also found associated with the curled elm leaves, such as Deraeocoris aphidiphagus which is associated with the woolly elm aphid (Johnson and Lyon, 1991). The multicolored Asian lady beetle (Harmonia axyridis) has also been observed laying its eggs nearby and feeding on woolly elm aphids (Simisky, Personal Observation). While the effectiveness of natural enemies at reducing woolly elm aphid populations on elm has been questioned, it is still valuable to encourage and protect their populations in managed landscapes.
Commercially available nematodes have been tested against the root-feeding life stage of this insect on Amelanchier spp. In a study when woolly elm aphid populations were heavy on Amelanchier spp. seedlings, neither species of nematode (Heterorhabditis megidis or Steinernema feltiae) reduced aphid infestations significantly at the crown or the roots. However, H. megidis was significantly more effective than S. feltiae at reducing E. americanum levels at the crown (Fry, 2001).
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (eggs) (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Chlorpyrifos (N)
Chromobacterium subtsugae (NL)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Cypermethrin (NL)
Dinotefuran (NL)
Emamectin benzoate (L)
Fenpropathrin (NL)
Flonicamid+cyclaniliprole (N)
Tau-fluvalinate (NL)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Isaria (paecilomyces) fumosoroseus (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Neem oil (NL)
Permethrin (L)
Pymetrozine (NL)
Pyrethrins+piperonyl butoxide (L)
Pyrethrin+sulfur (NL)
Pyriproxyfen (L)
Spinetoram+sulfoxaflor (N)
If managing this insect on Amelanchier seedlings, two applications of Beauveria bassiana were found to be effective at reducing the numbers of aphids on these plants (Fry, 2001).
Active ingredients that may be applied systemically include: Abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (eggs) (injection, soil drench), chlorantraniliprole (soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
