Abstract
Pith flecks are abnormal wood features, and they occur as a result of the mining of the cambium by the larvae of certain insect borers. Pith flecks appear as small specks on a cross-section, but the same pith flecks appear as long brown streaks on tangential and radial surfaces. Veneer values in some specific areas are substantially reduced because of high pith fleck densities. Especially, veneer logs cut from a stand at Akkeshi in eastern Hokkaido have long been faulted for heavy pith fleck infestations. Investigations conducted in the stand reveal that trees with numerous pith flecks can not be detected from their outward appearance. Only by the removal of the bark, can narrow streaks be found in the exposed xylem. These brown streaks extend all the way along the trunk, and they finally invade the roots of the host. The number of pith flecks decreases with the age as well as with the height of the host trees. Judging from insect-feeding behavior in the cambium region of living trees, the causal insects possibly belong to the Agromyzidae. This speculation, however, has not been confirmed because neither the larvae, the pupae, or the adults of these insects have been collected from the investigated stand. Histological observations show that the mines caused by these insects are filled with abnormal parenchymatous cells derived mainly from ray parenchyma. Shortly after the occluding of the cavities, normal wood is thereafter produced.
