The eggs are laid in the
axils on slender shoots (<10 mm diameter) of sallows, and the first year larva excavates a tunnel which shows no external signs of the larva. In the spring of the following year the larva can be as long as 17–18 mm and tunnels deeper into the tissue of the stem, excavating a vertical tunnel 50–75 mm long and 3 mm in diameter. By the second autumn the frass is pressed into cavities between the bark and wood, and the pear-shaped gall is noticeable. The larva feeds on sallows and their hybrids; eared willow (
Salix aurita), goat willow (
S. caprea), creeping willow (
S. repens), grey willow (
S. cinerea), white willow (
S. alba), crack willow (
Salix × fragilis), European violet willow (
S. daphnoides) and rosemary-leaved willow (
S. rosmarinifolia). Before pupation, the larva makes an exit hole and the
pupa (11–13 mm long) is yellowish and formed head down in a chamber above the gall. There is no cocoon. ==Distribution==