Within-tree Distribution and Survival of the Eucalyptus Longhorned Borer Phoracantha semipunctata (Coleoptera: Cerambycidae) in a Mediterranean-Type Ecosystem.

Stephen Seaton,George Matusick,Giles Hardy

doi:10.3390/insects11040225

Abstract

The attack patterns, infestation success and larval development of woodborers within living trees are complex and are largely shaped by host tree characteristics. Following a severe drought in a native eucalypt forest where outbreak densities of a native Australian beetle, the eucalyptus longhorned borer (Phoracantha semipunctata), occurred, a tree dissection study was conducted in Australia. This involved felling 40 trees each of jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) that were cut into 1-m sections and neonate larval galleries, larvae in pupal cells and adult borer emergence were measured and added to give total numbers per tree to determine the within-tree distribution and survival of P. semipunctata. There was a significant impact on larval survival in both species, in contrast, pupal survival remained high. Within-tree distribution of P. semipunctata was directional with borer emergence and incidence of larval galleries both negatively associated with tree section height above the ground and positively associated with section diameter and bark thickness, reaching a maximum towards the base of trees. High incidence and survival in lower thicker tree sections indicate a more conducive environment for larval development, in contrast to poor larval survival in smaller thinner sections at the top of trees. The dependence of larval survival on tree characteristics controlling the within-tree distribution of borer emergence is emphasized, and needs to be considered when estimating the spread of borer populations during outbreaks.

Highlights

The development of woodborer larvae is more restricted, compared to other phytophagous insects of defoliators, as they are concealed within their hosts and sapwood utilisation is determined by food resources emanating from the location of egg laying by their female parent [1,2]
Half the neonate larvae in both tree species survived to maturity, indicating the Approximately half the neonate larvae in both tree species survived to maturity, indicating the stability of the larval environment was affecting the development of P. semipunctata
This was evident with high gallery incidence and the formation of galleries that overlapped each other destroying the thin with high gallery incidence and the formation of galleries that overlapped each other destroying the partition of sapwood that separated individual larvae during development

Summary

Introduction

The development of woodborer larvae is more restricted, compared to other phytophagous insects of defoliators, as they are concealed within their hosts and sapwood utilisation is determined by food resources emanating from the location of egg laying by their female parent [1,2]. This is unlike the larvae of defoliators that can move as required to more favourable and nutritious parts of the tree. Phloem thickness generally increases with diameter this does not influence woodborer attack density [13]

Methods

Results

Discussion

Conclusion