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Myzocallis walshii

Black-bordered oak aphid

Description

Myzocallis walshii, known as the black-bordered oak aphid, is a sap-feeding insect primarily associated with oaks from the red oak group (Quercus rubra and related species). Native to North America, it was first recorded in Europe in 1988 and has since spread widely, particularly in urban areas and parks. This aphid is monophagous, feeding exclusively on oaks, with no alternate host plants. It inhabits the undersides of leaves, forming dense colonies that produce significant amounts of honeydew, leading to sooty mold development on surfaces below.

The aphid's lifecycle includes parthenogenetic and sexual generations, overwintering as eggs in bark crevices. Infestations reduce photosynthetic efficiency and can impact the aesthetic appearance of host trees by causing leaf discoloration and premature leaf drop. Despite the high honeydew production, Myzocallis walshii colonies are not ant-attended, unlike many other aphid species.

Symptom

Clusters of aphids are visible on the undersides of leaves. Leaves may show discoloration, deformation, and premature drop. Honeydew and sooty mold can coat surfaces below infested trees.

Tree Species: Oak

Part of a plant- attacked: Leaf / Needle

Pest significance: Less harmful

Pest Category: Insects

Invasive Species: Yes

Present in EU: Yes