What is the key distinction in feeding strategy between *Eriosoma lanigerum* and *Eriosoma americanum* concerning location?
The apple aphid feeds above and below ground throughout infestation, while the elm aphid shifts from temporary leaf feeding to long-term root feeding.
A major difference lies in how the two species utilize different parts of their hosts over time. The woolly apple aphid (*Eriosoma lanigerum*) maintains feeding activity both above ground (on twigs/shoots) and below ground (on roots) during its primary infestation period on apple and pear trees. Conversely, the woolly elm aphid (*Eriosoma americanum*) exhibits a distinct two-stage process: an initial, visible feeding phase on leaves that induces galls, followed by a migration of winged adults to establish colonies for long-term, hidden feeding on the elm tree roots. The apple aphid damage profile is more continuous across locations, while the elm aphid damage is sequential and segmented between visible and hidden sites.
