Susceptibility of Betula pendula clones to Phytobia betulae, a dipteran miner of birch stems

Larvae of Phytobia betulae Kangas (Diptera: Agromyzidae) mine within the di fferentiating xylem tissue of birch trees from canopy to stem base, resulti ng in permanent brown tunnels in the wood. In birch products the tunnels ar e considered to be an aesthetic defect. The aim of the study was to determi ne whether European white birch (Betula pendula Roth) clones differed in th eir susceptibility to Phytobia and to ascertain the relationship between th e size of the trees and their susceptibility. We counted the number of pith flecks (larval tunnels) in eight or nine micropropagated clones of B. pend ula in three 4- to 6-year-old field trials. After adjusting for the positiv e effect of tree size on Phytobia there were significant two- and three-fol d differences between clones in Phytobia resistance. A significant genotype x environment interaction in susceptibility of birch to Phytobia was obser ved. A slow-growing clone was the least susceptible to Phytobia.