Pear psylla eggs are spindle-shaped and whitish when first laid, then they turn yellow. During the summer, psylla eggs are laid on the leaves. The nymphs that hatch from the eggs are broad and flattened, with a blunt, rounded abdomen. This means that the nymphs feed and develop primarily on the newer, more tender growth. As they feed, the nymphs secrete a sticky liquid called honeydew.
Pear psylla can cause damage to pear trees and fruit in several ways.
The honeydew also can provide a medium for a sooty growth that blackens tree parts. When it occurs on the fruit, it russets the fruit skin and makes the fruit unsalable. Psylla feeding takes water and nutrients from the tree. This feeding can weaken the tree, cause leaf and fruit drop, and reduce the tree growth and fruit set for the following year. These insects can inject toxins as they feed, which can cause a pear tree to decline quickly.