Pear-bedstraw aphid overwinters on pear trees as eggs that are laid in autumn in bark crevices and around the buds on the shoots. These eggs hatch in spring as the leaves begin to emerge from the buds. While sucking up sap, the aphids secrete chemicals into the foliage and fruitlets, which cause the distorted growth.
Several generations of wingless aphids develop between bud burst and early summer. During June-July, winged forms of the aphid develop that migrate away to wild plants known as bedstraws, Gallium species, where they spend the rest of the summer. Infestations on pear die out during the summer but there is a return migration from bedstraws in autumn when overwintering eggs are produced.