Precision of dating insect outbreaks using wood anatomy: the case of Anoplophora in Japanese maple

To control invasive Anoplophora outbreaks, it is crucial to accurately date infestation dynamics. Dating of Anoplophora outbreaks is possible as these xylobiont insects induce wounds in living trees by forming e.g., exit holes. This study investigates to what precision these wounds can be dated with dendrochronological techniques. In an experimental setting, we studied the precision of wound dating on Acer palmatum, an ornamental tree occasionally containing larvae of A. chinensis. We studied the development of wound reactions at the beginning, during and after the growing season, both in relation to leaf phenology and intra-annual tree-ring growth. We found that the precision of dating exit holes is limited due to the highly variable intra-annual tree-ring growth whereby only an accurate distinction can be made between wounds originated during, or after tree-ring formation. The resolution was improved using local growth-the local reactivation of xylem growth around the wound-as a marker for wounds that occurred at the end of the growing season. We conclude that the intra-annual precision of dating Anoplophora outbreaks in Acer palmatum in the temperate North-western European climate is limited to three distinct phases: (i) The period of dormancy and leaf emergence (ca. October until April/beginning of May), when the wounds are located at the tree-ring boundary (ii) The period of tree-ring growth in which wounds are located within the tree ring (ca. end of April/beginning of May until late August/beginning of September), (iii) end of growing season (ca. end of August/September) in which local growth occurs.