Outbreak of Phoracantha semipunctata in Response to Severe Drought in a Mediterranean Eucalyptus Forest

Stephen Seaton,Katinka Ruthrof,George Matusick,Giles Hardy

doi:10.3390/f6113868

Stephen Seaton, Katinka Ruthrof + Show 2 more

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https://doi.org/10.3390/f6113868

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Journal: Forests	Publication Date: Oct 30, 2015
Citations: 62	License type: CC BY 4.0

Affiliation: Murdoch University, The Nature Conservancy

Abstract

Extreme climatic events, including droughts and heatwaves, can trigger outbreaks of woodboring beetles by compromising host defenses and creating habitat conducive for beetle development. As the frequency, intensity, and duration of droughts are likely to increase in the future, beetle outbreaks are expected to become more common. The combination of drought and beetle outbreaks has the potential to alter ecosystem structure, composition, and function. Our aim was to investigate a potential outbreak of the native Eucalyptus longhorned borer, Phoracantha semipunctata (P. semipunctata), following one of the most severe droughts on record in the Northern Jarrah Forest of Southwestern Australia. Beetle damage and tissue moisture were examined in trees ranging from healthy to recently killed. Additionally, beetle population levels were examined in adjacent forest areas exhibiting severe and minimal canopy dieback. Severely drought-affected forest was associated with an unprecedented outbreak of P. semipunctata, with densities 80 times higher than those observed in surrounding healthier forest. Trees recently killed by drought had significantly lower tissue moisture and higher feeding damage and infestation levels than those trees considered healthy or in the process of dying. These results confirm the outbreak potential of P. semipunctata in its native Mediterranean-climate Eucalyptus forest under severe water stress, and indicate that continued drying will increase the likelihood of outbreaks.

Highlights

Woodboring beetles are among the most widespread insect pests of trees, and can be especially responsive to drought stress in their hosts [1,2,3]
Phoracantha semipunctata damage to the inner bark/phloem was found to vary with crown condition (H2 = 37.97, df = 2, P < 0.0001), with the greatest damage in trees considered to be recently-killed when surveyed (Figure 2)
The implications of high populations of P. semipunctata are not well-known in its native ecosystems; this study clearly shows that beetles stayed confined to severely-stressed areas, unlike the pine bark beetles in

Summary

Introduction

Woodboring beetles are among the most widespread insect pests of trees, and can be especially responsive to drought stress in their hosts [1,2,3]. Forests in Mediterranean regions are already experiencing significant shifts in precipitation and temperatures, increasing tree water stress [6,7,8]. Associated with these climate changes, forests are being challenged from abiotic factors (e.g. high temperatures and drought) and by biotic factors such as damaging outbreaks of woodboring beetles in semiarid, temperate, and boreal climate regions [9,10,11,12]. While bark beetles (Coleoptera: Curculionidae) are well-known forest pests of drought-stressed hosts, other woodboring beetles (e.g., Cerambycidae and Buprestidae) can cause widespread damage under drought conditions [13].

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