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Problem: Woolly Elm Aphid (Eriosoma americana)
Hosts: Elm
Description: Leaves are twisted and malformed with
leaf clusters forming rosettes. Unfurling these leaves reveals aphids that are
covered with white waxy threads.
Life History: The Woolly Elm Aphid overwinters as an egg placed in a
bark crevice. These eggs are produced by females the previous fall. It is
interesting to note that these females produce a single egg and die soon after the egg is
laid because they lack functional mouth parts. Eggs hatch in the spring producing a
wingless female that feeds by sucking sap from the bottom of a young elm leaf. At
maturity, these females produce nearly 200 young, which are, again, all females.
Leaves form rosettes as populations rise. A winged generation (all females) appears by the
end of June and actively seeks out the Amelanchier shrub which is commonly known as the
shadbush or serviceberry. A new generation of females migrates to the underground
parts of the shrub. Several generations are produced underground. In the fall, a
final winged generation of females migrates back to the elm and starts the cycle over
again.
Recommendations: Damage is usually minimal and
control is difficult due to protection provided to the aphids by the rosette of leaves.
Control measures are rarely warranted.
References:
1. Insects That Feed on Trees and Shrubs, Cornell University Press, pg 262.
Last Update: 03/28/2003
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