Formation and structure of larval tunnels of Phytobia betulae in Betula pendula

Structural abnormalities in the wood of Betula pendula Roth caused by the l arvae of Phytobia betulae Kangas have been examined by light microscopy. Th e larvae bore through the zone of differentiating xylem from the crown to t he base of the tree. The wound callus formed by the tree in response to the damage becomes sclerified and appears as brown streaks running through the wood. In transverse section the tunnels are elliptical in shape up to 3 mm wide and correspond to 'pith flecks'.