Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain

Nathan Brown,Mike Jeger,Xiangming Xu,David Williams,Susan Kirk,Marco Pautasso,Sandra Denman

doi:10.3390/f8030087

Nathan Brown, Mike Jeger + Show 5 more

Open Access

https://doi.org/10.3390/f8030087

Copy DOI

Abstract

Acute Oak Decline (AOD) is a new condition affecting both species of native oak, Quercus robur and Quercus petraea, in Great Britain. The decline is characterised by a distinctive set of externally visible stem symptoms; bark cracks that “weep” dark exudate are found above necrotic lesions in the inner bark. Emergence holes of the buprestid beetle, Agrilus biguttatus are often also seen on the stems of oak within affected woodlands. This investigation assesses the extent to which the external symptoms of these two agents co-occur and reveals the spatial and temporal patterns present in affected woodland. Annual monitoring in eight affected woodlands showed that stem bleeding and emergence holes frequently occur on the same trees, with new emergence holes significantly more likely to occur when trees already have stem bleeds. Trials with coloured prism traps confirm A. biguttatus was present at all experimental sites. Beetle emergence is linked primarily to a few heavily declining trees, indicating that susceptibility may vary between hosts and that those with reduced health may be predisposed to AOD. Stem bleeds occur on trees in close proximity to the locations of trees with exit holes.

Highlights

Acute Oak Decline (AOD) is a distinctive condition, within the wider decline complex affectingBritain’s native oaks, Quercus robur (Matt.) Leibl. and Quercus petraea L. [1]
A consistent trend was seen in all four years, forHoles emergence holes and stem bleeds to occur on the consistent trend was than seen in all four years, emergence and stem bleeds to occur on same trees at aAfrequency greater expected thanfor if they wereholes independently distributed (Figure 2)
Further steps are necessary to establish whether the co-occurrence involves a direct interaction, with the beetle aiding the spread of bacterial agents, or whether both agents are acting in an opportunist role, exploiting the same weakened hosts

Summary

Introduction

Acute Oak Decline (AOD) is a distinctive condition, within the wider decline complex affectingBritain’s native oaks, Quercus robur (Matt.) Leibl. and Quercus petraea L. [1]. Acute Oak Decline (AOD) is a distinctive condition, within the wider decline complex affecting. Britain’s native oaks, Quercus robur (Matt.) Leibl. With isolated occurrences in south Wales and along the Welsh borders [2,3] AOD affects the health of oak species [1,3] that form the largest component of native woodland [4]. A broad definition of tree decline describes a syndrome involving multiple agents, which may act sequentially or in parallel, and will have a cumulative effect on the health of the host [5]. Declines often involve hosts and agents that have co-evolved and, as such, host trees are resilient with defences against insect and microbial incursions; environmental change can affect this balance [6,7].

Objectives

Methods

Results

Discussion

Conclusion