Woolly elm aphid

The woolly elm aphid (Eriosoma rileyi) is a member of the order Hemiptera and the family Aphididae. It is a specialized pest that derives its common name from the abundant, fluffy white wax filaments secreted by the nymphs and adults. These filaments protect the aphid colonies as they feed on various species of elm trees.

The host range is largely limited to the genus Ulmus. Unlike some other aphids that alternate between two different host plants, the woolly elm aphid typically spends its entire life cycle on elm trees. They are most commonly found in clusters on the bark of the trunk, branches, and within crevices where the tree's tissue is vulnerable.

The biological cycle begins with overwintering eggs or nymphs tucked away in the bark. As temperatures rise in spring, the population becomes active. The aphids tap into the tree's phloem to feed on sap. They undergo multiple generations throughout the growing season, which allows the population density to increase rapidly if conditions are favorable for the pest.

The damage caused by Eriosoma rileyi can be significant. By removing large quantities of plant sap, the aphids weaken the tree, causing stunted growth, leaf yellowing, and branch dieback. Furthermore, the honeydew excreted by the aphids encourages the growth of sooty mold, which can cover the bark and foliage, further stressing the tree and reducing its aesthetic value.

• Apply systemic insecticides during the early stages of infestation.
• Encourage natural predators such as lady beetles, lacewings, and parasitic wasps.
• Use dormant oil sprays in late winter to target overwintering stages.
• Maintain tree vigor through proper watering and pruning to help them recover from aphid pressure.